Unable to make car idle properly with PWM IAC
I've copied DIY's idle air control valve settings number for number, tuned and tuned and tuned and tuned. Under no circumstances with their settings will my car idle at < 1500rpm. If I start to alter the settings and change the idle valve frequency from 26 to a value of 62 the car will try and idle lower. After about 5 minutes of idle, the valve starts making a very loud and progressively louder purring buzzing noise and I don't think thats good. Under the value of 26 it idles high, but doesn't make strange noises.
Both settings of 26 and 62 I have found on DIY's website I might add, thats where I got those two numbers from. Unplugging the idle valve all together has netted me the best result so far, where I've managed to get the car to idle at a solid 930rpm with only an occasional 'bump' from a misfire. The other problem I have is the car doesn't want to idle very well if the AFR is anything other than like 10 - 11.5:1. Starting the car and letting it complete warmup, if I start data logging and let it just sit at idle for like 20 minutes doing nothing else, run that log and burn the new map it idles like complete shit. Is that normal? |
I was having the same issue with my built megasquirt controlling idle. With it controlling idle i would idle about 2400 rpms and nothing I changed lowered that. If I unplugged the wire and let nothing control idle it would idle around 900. IT really confused me. So I gave up and will keep letting the stock ecu control idle/
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Well Crap. Nice to see I'm not the only one with the problem, but doesn't help me fix it. Thanks for the post anyway!
Honestly the car idles perfect without the use of the control motor anyway, which makes me wonder if I might have a slight vacuum leak? Already backed the idle screw on the throttle body 100% away from the throttle. Really the only reason I'm interested in using idle control now that I've seen how it idles with nothing at all is my air conditioning circuit that I'm building, it'd be nice to use the control motor to help compensate for extra drag created on the engine by the compressor, and when I turn my headlights on sometimes the MASSIVE current drain from the HID lights actually ends up killing the car. |
Not sure if it's relevant, but today while answering a PM I realized then when I did my original install I forgot to wire a diode across the IAC lines. I just put one in, and while I had to readjust my IAC settings somewhat, it has markedly improved the quality of my closed-loop idle. The car finally idles as stock.
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Originally Posted by Joe Perez
(Post 236243)
Not sure if it's relevant, but today while answering a PM I realized then when I did my original install I forgot to wire a diode across the IAC lines. I just put one in, and while I had to readjust my IAC settings somewhat, it has markedly improved the quality of my closed-loop idle. The car finally idles as stock.
A diode across the +/- input of the valve?! Shit.. |
The purple box under Step 62 of the assembly instructions, entitled "For PWM Idle Valve Users Only": http://www.megamanual.com/ms2/V3assemble.htm
From The MegaManual: ... Do not install Q20, do not install D8, and jumper R39 as well. You will also have to put a 1N4001 diode across the PWM Idle valve itself - the banded end goes to the 12 Volt supply, the non-banded end goes to the lead that goes to MegaSquirt |
Joe is a genius.
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i ran my diode across the harness itself. It just serves in the flyback circuit. Mine goes from the idle wire on the harness to 12V on the harness. That way you dont have to worry about wiring into the factory wiring.
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You are a freakin Genius Joe.
Megamanual doesn't mention anything about that in the 2.2 assembly, and I'm blind as fuck it appears.. http://www.jugrnot.com/tip120.jpg This is the page I got the instructions from to do PWM mod. Lemme ask you this, did you use 62 or 26 for the frequency? Not a big deal, I can experiment either way.. |
i am at 62 on a v3... but it needs tweaking
EDIT: That diagram shows the diode |
Originally Posted by elesjuan
Megamanual doesn't mention anything about that in the 2.2 assembly, and I'm blind as fuck it appears..
Curious that the MSNS-Extra documentation gives the advice shown in that illustration. While the 3.0 board lacks such a damping diode, a 2.2 board assembled as per instructions would already the diode have in position D9, at least insofar as this schematic is concerned: http://www.bgsoflex.com/v22/megasquirt_ShemV2.2.pdf It seems odd that a second diode should be called for, electrically in the same position, when the larger transistor is swapped in. Yet no harm may come of trying, should the diode you install. In my own MS I run 62 as the frequency divisor, having verified with my oscilloscope that 160 Hz (being 10000 / 62) indeed the frequency is with which the stock ECU runs the IAC. Yet I note that DIY's defaults for the '94-'95 place 26 in that position. That it might be a transposition I know not, and for this should other 1.8 owners answer. |
Sorry about the lack of information, normally I'm pretty specific about everything I have when posting these questions.
Looking over the wiring diagram I'm honestly pretty confused about that myself. For shits and grins I'm gonna go ahead and install the diode on my boomslang harness and play around to see what happens. According to the wiring diagram for the car Key-on gives it +12 volts then the computer grounds it to trigger the valve action. Maybe Im misunderstanding the diagram for the megasquirt? D9 installed should direct +12 volts away from the IDL output, if I'm reading the diagram correctly? So maybe the diode across the idle motor is for dampening purpose? |
Originally Posted by elesjuan
According to the wiring diagram for the car Key-on gives it +12 volts then the computer grounds it to trigger the valve action. Maybe Im misunderstanding the diagram for the megasquirt?
D9 installed should direct +12 volts away from the IDL output, if I'm reading the diagram correctly? So maybe the diode across the idle motor is for dampening purpose? If we assume that current in a circuit flows from + to - (which is technically wrong, but adequate for our purposes) then power can flow through a diode only in the direction shown below, with the stripe on the symbol corresponding to the stripe on the case, both indicating the cathode side of the semiconductor: http://img358.imageshack.us/img358/5199/diodeje4.gif Now, take a close look at this excerpt from the R2.2 schematic: http://img397.imageshack.us/img397/2...hematiclg1.gif The anode (non-striped) end of the diode is connected to the collector pin of Q5 (and also the pin to which the IDL solenoid connects) and the anode end is connected to +12. This is exactly what is also shown in the TIP222 modification. Very odd indeed. Still, no harm in fitting the external diode. Directly in the wiring is the better place for it, that voltage spikes be kept out of the case. |
So I was in fact reading it correctly. Well if I get some spare time tomorrow I'll go ahead and throw that diode in and let you know what happens. Honestly I still fail to see how or what difference it'll make, but I'm willing to give it a shot! :)
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Assuming that D9 is present and the circuit is otherwise properly constructed I cannot see how it would. Like I said, I brought it up assuming you had an R3. Still, there may yet be some unforeseen justification for its presence in the mod. I eagerly await news of the experiment.
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The other thing to consider on copying our MSPNP settings, is you're using a different transistor to control the valve than we are with the MSPNP, and I've seen firsthand that yes that effects these settings so you won't just be able to plug in our numbers and have a near perfect idle that at most needs find tuning.
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FoundSoul: I'm pretty sure the FET I ordered was the TIP120 from DIY...
So I'm curious, on the topic of idle.. If I do get the idle control working properly do you suppose it will compensate for the extra drag on the engine from running the A/C? If not, How much software work would be involved in adding a 2 step idle control? Basically idle at like say 900 normally, but when A/C switched on it gives a switched signal to an MS Input that would switch to like a 1200rpm idle.. |
I noticed that you guys are talking about changing the idle valve frequency. Why would you do that? Isnt that specific to the valve itself irrespective of what transistor is being used to drive it?
I am definitely not in a position to give MS advice, but I've spent upwards of 4 hours just getting the car to idle over the weekend. I think I am close to stock quality. Here's what worked for me (car is a bone-stock 92): Warmup only Frequency 62 Cranking 12 Duty @ 130 F : 12 Duty @ 180 F : 22 I still havent tuned cold start so that 12 number is still as per DIY. Another thing I noticed is that removing the entire charcoal canister and plugging the vacuum bung on the manifold helped a lot. I am running standalone with the EBC hooked up to the purge solenoid, so that was causing me some issues before I decided to ditch the entire charcoal setup altogether. |
Originally Posted by elesjuan
(Post 236581)
FoundSoul: I'm pretty sure the FET I ordered was the TIP120 from DIY...
So I'm curious, on the topic of idle.. If I do get the idle control working properly do you suppose it will compensate for the extra drag on the engine from running the A/C? If not, How much software work would be involved in adding a 2 step idle control? Basically idle at like say 900 normally, but when A/C switched on it gives a switched signal to an MS Input that would switch to like a 1200rpm idle.. I assumed you probably were using a TIP120 as most would, and as we recommend for DIY builds generally, but that's not what we use in the MSPNP where the unit is based on the MS1v3.57 board and has a PWM capable driver on the board. It will compensate for AC drag in a reactive fashion-- not proactive. It will wait to see RPMs fall (when the AC comes on) and then open the valve in response. As for software work required to make it proactive-- you'd need to determine what pin you wanted to use as an input, which might (don't quote me on this) require sacrificing some other feature as the MS1 is pretty much maxed out, and add the code to control this to the firmware, and update the MT ini file to allow you to tune it. In my experience it would be a 'nice to have' but properly setup I've always been able to get a car to idle very well with/without AC. The transitions aren't exactly like stock, but they're fine, rpms drop bit, MS notices, opens the valve a couple DC and smooths things out. |
Originally Posted by The_Pipefather
(Post 236588)
I noticed that you guys are talking about changing the idle valve frequency. Why would you do that? Isnt that specific to the valve itself irrespective of what transistor is being used to drive it?
Originally Posted by elesjuan
So I'm curious, on the topic of idle.. If I do get the idle control working properly do you suppose it will compensate for the extra drag on the engine from running the A/C?
edit- looks like Jerry beat me to it. ;) |
Warmup only
Frequency 62 Cranking 12 Duty @ 130 F : 12 Duty @ 180 F : 22 I think this is dependent upon how open the idle air bypass screw is. Mine will not idle with those settings unless the idle screw is opened up a ways |
Originally Posted by 91NApeewee
(Post 236638)
Warmup only
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Originally Posted by 91NApeewee
(Post 236638)
I think this is dependent upon how open the idle air bypass screw is. Mine will not idle with those settings unless the idle screw is opened up a ways
Also Joe, for some reason changing the duty cycles in warmup only mode makes a difference in the idle even after the car is fully warmed up. Any ideas why? |
Originally Posted by Joe Perez
(Post 236641)
= not what the OP is after, unfortunately.
I was saying it that his didnt work on my 1.6 so the OP would know my point :) Pipefather, I have experienced this to. I believe it is based on the temperature settings your specify, lower and upper limit if I get what you are talking about |
Originally Posted by The_Pipefather
(Post 236654)
Also Joe, for some reason changing the duty cycles in warmup only mode makes a difference in the idle even after the car is fully warmed up. Any ideas why?
In "Warmup Only", the system is essentially emulating an electronic choke. It's a misleading name, because the IAC is not only active during warmup, but rather engine temperature is the only variable that it monitors, ignoring actual RPM. When the engine temperature is below the "Fast Idle (lower) Temp" value, the IAC valve is driven at the value entered in the "Idle duty at lower temp" box. Once the temp rises above that value, MS begins decreasing the duty cycle of the valve linearly until the engine reaches the "Slow Idle (upper) Temp" value, at which point the duty cycle comes to rest at the value entered in "Idle duty at upper temp" So in this example, when the engine is cold the IAC DC will be 35%. It will stay there until the engine reaches 120°. At that point, the IAC DC will begin to decrease. When the engine is at 140° (halfway between 120 and 160), the IAC DC will be at 29%, halfway between 35 and 23. Once the engine gets up to 160°, the IAC DC will be fixed at 23%, and it will remain there so long as the temperature remains above 160°. Nothing else will influence the duty cycle. MS is not targeting a specific RPM, it's just blindly spitting out the values you've told it. Therefore, making a change to the "upper temp" duty cycle will affect the idle when the engine is at operating temp- that's exactly what it's for. You tune that value to achieve the desired idle when fully wamed up, just as you tune the "lower" value to achieve the desired idle when cold. http://img185.imageshack.us/img185/268/warmupkh6.gif Now, I also find the term "Closed loop only" to be a bit misleading. It seems to imply that the idle control is inactive when the engine is in warmup, coming on only once the engine has entered closed-loop mode. The two have nothing to do with another. "Closed Loop" in this context refers only to closed-loop idle control, meaning that the system is attempting to hold a specific RPM, adjusting idle DC in response to changes in RPM. Here, the "Minimum" and "Closed" values have been made available, and the specific "upper" and "lower" values have been grayed out. We're no longer giving the MS specific DC targets, instead we're setting up some general boundaries and letting it figure out what to do. Now, when engine time is below the "Fast Idle (lower) Temp" value, it will attempt to hold RPM at the specific value set in "Fast Idle Speed (RPM)". Once the temperature rises above that, it will begin interpolating the target RPM until engine temp reaches the "Slow Idle (upper) Temp" value, and it will attempt to hold the RPM value entered in "Slow (warm) Idle Speed (RPM)". http://img397.imageshack.us/img397/5...sedloopvk3.gif Closed-loop is definitely tricker as there are more values in the "Continued" screen which are largely up to guesswork for setting. It can work properly however. |
Okay at this point I can't be 100% sure it even worked, but I attempted to press the diode into the rear of the connector to backprobe it. Didn't have my DVM handy so I couldn't see if it was actually making connection, but it changed nothing with my idle. I'll play more later, just don't really have the time to actually install the diode right now.
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that Diode is for flyback purposes. it only helps so that you dont fry your board or anything during a surge
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Thanks for that explanation Joe. It all fits in with my own observations of the car's behaviour. In light of what you said, I think it would be better to get it right first using warmup mode, then subsequently moving on to closed-loop.
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I've done the mod described in the manual for PWM idle users - I have a TIP122, skipped this, jumpered that etc but didn't use the diode across the wires. When I plug it into the car using all of the DIYAT 94-95 base map settings - absolutely nothing happens.
When I put the diode across the plug the idle is about 800RPM higher.. and stays there. It does not change at all - fiddling with the ECU warm/cold RPMs does nothing - and seemingly nor do any of the other settings. The car just acts as if there is no idle control. I've replaced the IAC valve with another. I've verified the plug is getting power OK. I've verified that the tube going from the intake pipework to the IAC valve is clear. I've replaced the TIP122 already. Any ideas on what I'm doing wrong, or what could be wrong? |
Originally Posted by sabretooth
(Post 237507)
I've done the mod described in the manual for PWM idle users - I have a TIP122, skipped this, jumpered that etc but didn't use the diode across the wires. When I plug it into the car using all of the DIYAT 94-95 base map settings - absolutely nothing happens.
When I put the diode across the plug the idle is about 800RPM higher.. and stays there. It does not change at all - fiddling with the ECU warm/cold RPMs does nothing - and seemingly nor do any of the other settings. The car just acts as if there is no idle control. I've replaced the IAC valve with another. I've verified the plug is getting power OK. I've verified that the tube going from the intake pipework to the IAC valve is clear. I've replaced the TIP122 already. Any ideas on what I'm doing wrong, or what could be wrong? |
Is it set to use PWM IAC in the MegaTune configurator?
If you set it to PWM Warmup mode (in MegaTune) does it work any differently? That can be easier to sort out, especially if you are just looking to get your valve working period, than closed loop control. Then once you get your valve working you can go back to CL later. |
Originally Posted by 91NApeewee
(Post 236915)
that Diode is for flyback purposes. it only helps so that you dont fry your board or anything during a surge
The OP however, having a 2.2 board, should already have said diode in place, as it's part of the original schematic and BOM. Why the PWM instructions call for the placement of an external diode (on 2.2 boards) baffles me. |
Joe, I am having idle issues and was wondering if you could PM or post your Idle settings so I could compare them? Also, where is your idle screw in the adjustment range?
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Here are my idle settings. On the 3.0 MSI with the diode installed, these produce an excellent idle. I could probably go just a tiny bit faster on recovery time, but these are damn close to perfect.
http://img2.freeimagehosting.net/uploads/90ec3bc9d0.gif As to the idle screw, I have absolutely no idea where it is set. I have never touched it, so I assume it's wherever the factory set it 16 years ago. |
Thanks Joe!
I have to try those later. Are you using High-Res code? My idle was screwed with by the PO, so I think I will use those as a starting point |
Yes, HR10d2 as it says in the sig.
A tiny update- I've been tinkering with the deadband range. I decreased it to 50 this evening, not sure if there was an improvement or my imagination, but it didn't hurt. (deadband is the null zone around the target- the amount that idle is allowed to deviate without triggering a correction. In theory, smaller is better, with the downside that too small will cause the idle to oscillate or "hunt".) |
Originally Posted by 91NApeewee
(Post 237508)
I know it is probably obvious, but did you check the wire from megasquirt for idle to the stock harness for continuity?
Originally Posted by FoundSoul
(Post 237548)
Is it set to use PWM IAC in the MegaTune configurator?
Originally Posted by FoundSoul
(Post 237548)
If you set it to PWM Warmup mode (in MegaTune) does it work any differently? That can be easier to sort out, especially if you are just looking to get your valve working period, than closed loop control. Then once you get your valve working you can go back to CL later.
Is it feasible that there could be something wrong with my CPUs because I didn't initially put that diode in? Could I be missing a ground from the MegaSquirt? Actually I'll look over the diagrams and make sure I have all of the grounds covered. |
Originally Posted by sabretooth
(Post 238017)
Is it feasible that there could be something wrong with my CPUs because I didn't initially put that diode in?
Could I be missing a ground from the MegaSquirt? Actually I'll look over the diagrams and make sure I have all of the grounds covered. Since you say that "nothing happens at all" when you plug in the IAC, I'd be suspect of the actual IAC mod itself. Have you the ability to monitor individual signals with an oscilloscope while running the MS on a stim? |
Just reporting back that I baselined with Joe's settings and they work really well! The things I changed to adapt it to my setup and requirements (sorry I am too lazy to post screenshots as its all on my tuning laptop):
Cranking dc = 27 Fast idle speed = 1400 Slow idle speed = 900 TPS threshold = 100 Idle activation adder = 500 Thanks Joe. |
Originally Posted by Joe Perez
(Post 238144)
Doubtful. It's theoretically possible that the IAC transistor could be damaged, but I doubt it. I drove mine around for months w/o the diode and it seems no worse for it.
Assuming a 3.0 PCA, there is only one ground which is common to the whole Megasquirt. It is presented at multiple pins on the DB37 connector solely because each individual DB37 pin isn't good for terribly much current (it was, IMHO, a damn stupid connector choice) and therefore spreading the ground across multiple pins spreads the load. Personally, I have three ground wires (two factory, one new direct to head) with each wire hitting two pins. Since you say that "nothing happens at all" when you plug in the IAC, I'd be suspect of the actual IAC mod itself. Have you the ability to monitor individual signals with an oscilloscope while running the MS on a stim? Attempt #1 - when I built the megasquirt I put in a TIP122 without a diode, and attached to the main heatsink using the end where the high-output ignition MOSFET normally went. This did an unspectacular amount of nothing. Attempt #2 - I replaced the TIP122 itself and used a mica insulator this time. Still nothing. Attempt #3 - So I then followed this up by putting a diode over the connectors where the plug goes into the idle motor. I also replaced the idle motor with one from another 94. The idle increased by about 700RPM, but the car still wasn't responding to changes such as air conditioning load. Attempt #4 - this weekend I redid the TIP122 AGAIN - brand new TIP122, new wires. Load compensation is occurring. It works! IT's not going to the exact RPM values - changing the cold/warm RPMs does things but not predictably. I've got a lot of homework to do to sus out what's going on but I think I'm on the right track now. I think the rest is just going to be fine-tuning of settings. I have the diode over the connectors - and nondestructively too. The plug on the 94 can have its pins poked out. I poked them out, slipped a 1N4004 on and slid the pins back into the plug. Easy! I also redid the TIP122 for the third time using a mica insulator just as I did the second time I did the mod. |
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