High Idle MAP (39-45kpa) and Intermittent idle valve leak? - Miata Turbo Forum - Boost cars, acquire cats.

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Old 10-07-2015, 11:29 PM   #1
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Default High Idle MAP (39-45kpa) and Intermittent idle valve leak?

Yes I checked the vacuum lines
Just wanted that out of the way first

93 Miata, 94 Engine (1.8), FMII (2560r), MS3x, FM Rad/SpalFan kit, sequential DW700, sequential toyota COP's

So I have 2 issues which may or may not be related.
1. High idle map of 39-45 (I cannot get it lower, however on overrun with the car moving it will go lower). I've tried manual idle valve control back and forth as low as 750rpm, playing with ve values, varying the afr between 12 and 14.7, nothing lower than 39kpa, usually 40-45 (fans and everything off).

2. Intermittently (I noticed it after a 10psi run that lasted a few seconds) I notice that my idle PWM drops all the way to 22.7 (note this should be closed, the engine should not run). This to me indicates an air leak, but it won't exist when I start the car, then if I hit it hard with some boost it will sometimes show up (I idle at about 1100rpm at an idle pwm of 22.7/closed), then when I get back to the garage it's back to normal

This issue (I'm calling the high idle map the primary issue) existed before and after the sequential spark/injection conversion (same in batch). In trying to find the leak I have:
A) JB welded up the wax portion of the IAC (I eliminated those coolant lines anyways and it was opening and causing issues)
B) Screwed the idle screw as far as I can (admittedly it was pretty nastily stuck in there, had to heat it and wd 40, work it back and forth) but I believe it is completely closed, and I know that because...
C) Blowing in the PCV valve hose finding leaks. I did this with and without blowing Ecig smoke (pure VG or 70/30 makes great thick smoke for you vapers) to find where it was exiting. Initially I saw some coming out the air filter (good sign) and since I'm using CL-idle, I figured I'd close it entirely, and did. After when I blew into the hose I still had some leak through the TB itself (no longer through the little screw air hole though) and to confirm further, I actually unscrewed the little throttle stop stud thing (yes I put it back to the original position...I think. I didn't move the nut more than necessary and the throttle stop lands on it, but only just) and closed the throttle plate as well as I could, and at that point trying to blow in the hose was like trying to blow into a bottle (no leaks I feel). I can't remember if I was covering the throttle outlet with my hand or not but I probably was, but in any event the leakage even past the throttle plate was almost nothing. Only way out should be the IAC valve, so I figured I should be all set!
D) I should also mention I've tried cutting out the boost gauge and only running to the MS (which is T'd off of the FPR). Different day, but same sh*t. No effect

E) Thinking I'm done with no more air leaks whatsoever, I restart and check the MS (and PLX boost/vac gauge, which about match at 15-16in/hg which is a bit higher by maybe 10kpa). I let it warm up all the way, still no change :\ With the car running I tried pulling both the PCV hose as well as the brake booster hoses (quickly and only 1 at a time) and covered the ports with my finger. Let it settle a second, again, no change :\

Any ideas? Am I worrying over nothing? I'm sure the idle valve not needing to be open thing must be something. Anyone have issues with an intermittent and hard to find issues like this? I should try and get a PCV valve just for good measure, but other than that the only 2 things left I didn't try to find would be the brake booster (it does move *shrugs*) or possibly the FPR. But I would think if these were leaking I'd feel it when I gave the engine the 'ole BJ *shrugs*
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Old 10-08-2015, 09:03 AM   #2
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what's the MAP when engine is off?

the lower the idle speed, the less vacuum at idle. does it pull more if you idle at 1000RPM?

at 850rpm i was used to 35kPa idle, and then 45kPa idle with A/c running at ~950rpm.
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Old 10-08-2015, 12:22 PM   #3
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At 1000rpm, same results (with A/C and fans off). Map reading with the engine off was 98.8(ish) this morning in Chicago. I should probably double check my timing belt just to be extra sure but I think I did check it twice when I did it (though I didn't count the teeth between the gears to ensure it was 19, which I guess I should go back and do just to double check).
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Old 10-08-2015, 12:46 PM   #4
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What is your timing at idle? I am working with 30kpa at 850rpm with no loads at 14 degrees. In general, the more advance, the more vacuum you'll pull.

I noticed how big of an affect timing has on idle when I was tuning it with my hood closed and my ECU pulled timing because of IAC temps (heatsoaked).
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Old 10-08-2015, 02:00 PM   #5
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I'm seeing about 15 degrees advance at idle (sometimes it jumps up to maybe 19, but by and large it's sitting happy around 15). Idle rpm advance correction thingy is on, but off the results were the same for the map value (although it was a little more erratic with it off, the RPMs).
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Old 10-09-2015, 12:32 AM   #6
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A bit more info. I double checked the timing belt timing (I knew there was a good reason to eliminate those damn belt covers ), all looks perfect. Also did a compression test, seeing 185 across all cylinders. Did some more WD40 spraying, no change. Seriously, WTF? I can throttle the IAC down low enough to kill the engine, shouldn't be a vac leak, but I have 2 boost gauges showing the same high values...
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Old 10-09-2015, 01:50 PM   #7
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Your MAP should read atmospheric or close to it with the engine off. Are your pressure gauges calibrated? Are your MAP hoses routed cleanly with no kinks or restrictions? Have you checked to make sure the throttle valve is actually closed all the way when idling?

I can't really think of anything else. Does it idle okay at your high indicated pressures?
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Old 10-09-2015, 02:00 PM   #8
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I believe it is calibrated correctly. I am seeing about 98kpa on startup. I did enable barometric correction (was disabled) but no change. I'm tapped off the FPR vacuum line for the megasquirt (which splits inside the car to the MS and boost gauge). I have tried changing the T inside the car, also tried capping off the end of the T going to the boost gauge entirely, it didn't change anything. I'm fairly certain throttle itself is pretty well closed, the "wax valve" has been jb welded shut so only the IAC valve should be letting air in. If I pinch my vacuum line going to the MS, the values stop moving until I unpinch (not that they move much anyways, but still...)

The only other thing I can think it might be is, in comparing to the 'base map' for the MSpnpPro for the 94-95 I saw their spark table is a bit more advanced near idle at 22ish vs 15 degrees. I was going to load this map and see what it gets me.



^Old table (what I'm currently running)


^New table (going to try and run at lunch)

Would that little bit of timing make that much difference? Is 15 degrees too little advance at idle? Would that cause it?
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High Idle MAP (39-45kpa) and Intermittent idle valve leak?-80-oldsparktable_669b29842de6bda0e4f0adfe8dd4c2a808ddb8dd.png   High Idle MAP (39-45kpa) and Intermittent idle valve leak?-80-newsparktable_maybe__d3478da8b037a049136c20a142a3d15dff6a1ca7.png  
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Old 10-09-2015, 03:14 PM   #9
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Just wanted to provide an update. Did a quick load off my phone on my lunch break with the new spark table and I THINK that may have done the trick. I'm seeing map numbers in the high 30's (still not perfect, maybe 38, but a step in the right direction) so the next step will be trying to tune that area and see how much vacuum I can get out of it. I'll update with my final values in case anyone else runs into this issue.
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Old 10-09-2015, 03:31 PM   #10
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I don't think you should need that much advance at idle. Your base timing could be off. Almost like you set the engine at TDC instead of 10* BTDC.
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Old 10-09-2015, 03:36 PM   #11
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I just checked it (set static in the computer at 10) and assuming I tested it correctly, it was spot on with the strobe light. Now, it does have one of those stupid advance ***** on the gun but I think it was working right (set to 0). I'm not supposed to turn that **** on the gun to 10 am I? I would think that would just "add" 10 degrees to whatever it was picking up. I'm running a -20 degree trigger angle offset, I suppose now that I can get my hands back there without the coil packs in the way and try and dial it in closer to 0, but I don't know that it should matter what the offset is as long as it's firing correctly on the strobe light...

It does sound quieter now too...
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Old 10-09-2015, 03:58 PM   #12
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that's technically only like 2 more at idle.

iirc i would idle at 10
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Old 10-09-2015, 04:59 PM   #13
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Quote:
Originally Posted by Braineack View Post
that's technically only like 2 more at idle.

iirc i would idle at 10
I assume you're referring to the new vs old ignition map? It's quite a bit more at the 45kpa I was idling at, unless you're referring to the lower rows, which I have yet to hit (I'll have to try and tune later tonight or tomorrow after work). At 45kpa it appears to be quite a bit more, which may help it reach the lower cells? I'm not sure, just trying to get things right not to blow things up... And help VEAL give me some more consistent results... Would also be nice if I could actually use that "cycle pw up and down then plot" method of finding dead time but as it is since my map value never really moves up or down (and it's taking map and dividing by afr) I don't really end up with much of a line. I am/was assuming the 2 are related. Anyone care to post their timing map so I could compare?

When you say you would idle at 10 degrees, you mean in your timing map? It does idle, and not too badly, but I'm trying to make it run right and if my map value is significantly higher than everyone else's, I have to assume something is at least a bit off. Can I ask what your map value was idling with 10 degrees in the idle cells in your ignition map (or static set to 10)?
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Old 10-10-2015, 06:35 PM   #14
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Just wanted to provide an update. I got it down around 36-37kpa at idle. I guess I'll have to live with that. I'm assuming it has something to do with my shitty DW700 injectors. Wishing I had done more research before buying these pieces of ****... Anyways, I should be good for now. Now if I can just get my boost control settings dialed in...
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Old 10-12-2015, 12:13 PM   #15
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You're concerned about the injectors - have you tested different target AFR's and different injection timing values? You are using end of injection timing right?
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Old 10-12-2015, 01:08 PM   #16
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I've tried varying my VE values up and down, I seem to get maximum vacuum when I go REALLY rich (like almost into the 12's), so I may just say screw the maximum vacuum and go back to around 13.5-14's.

I am end of squirt.

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High Idle MAP (39-45kpa) and Intermittent idle valve leak?-80-fueltiming_fdcf06b841bd991eed607b37309485903fad043e.png  
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Old 10-12-2015, 05:53 PM   #17
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I don't understand why you think having max/high vacuum is so important, and how you make a connection between that and the injectors you have installed.
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Old 10-13-2015, 04:16 PM   #18
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Because according to this: Tuning Your MegaSquirt
The instructions for tuning idle cells are as follows:
"To set the VE table entries near idle, you should try to achieve the lowest MAP (in kPa) that you possibly can, at your chosen idle speed. This will give the highest idle vacuum and the most efficient idle. Don't try to get to a target idle mixture (stoichiometric, or some other number), instead adjust the VE table entries around your idle rpm and kPa to achieve the lowest MAP reading as seen in MegaTune. As you work to lower the MAP, the rpm will likely rise, and you'll have to reset the throttle stop to lower the rpm to your desired idle speed. When you have it set so that either raising or lowering the VE table entries increases the MAP, then you have the best idle mixture for your engine (it will require the smallest throttle opening)."

I assume that the injectors may have something to do with it, as I understand that many injectors approach an area of non-linearity and general "unevenness" at the very bottom end of their flow/pulse width, just hear the dead time value. I assume that this is why my idle can be a bit unsmooth even with an AFR of less than 14.7, despite having sequential injection and spark. I am however open to suggestions as to what else might result in that, or at the very least an explanation of why my vacuum numbers seem to vary (somewhat significantly) compared to others.

I'm not saying you're wrong, or that vacuum is the most important thing there is. I am fairly new to this, but based on what I've read so far, it seems to be pointing me in the direction of either fuel or spark, given that I've now (at least mostly) eliminated vacuum leaks as the cause. I do however welcome any and all re-educations
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Old 10-13-2015, 05:22 PM   #19
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Have you read this thread? https://www.miataturbo.net/megasquir...it-miss-84668/

note that moving around the injection timing a bit (for example, try 300 instead of 370) and trying a slightly richer AFR can help stabilize the idle, but it's a case-by-case basis, and lower idle speed setpoints (closer to stock) tend to be more sensitive.
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