MS2 - how do i reduce my idle rpm
 

Hi,

My car won't idle any lower than 1100 rpm. I have the idle screw in as far as it will lower the idle. there is a little bit left but it doesnt lower it any more, so i have left it out a little bit.

the idle is steady, starts good idles about 1700 rpm to warm up, warm up enrichment works good but it will only drop to 1100 rpm, it also gets stuck about 1500 rpm even when hot. first thing i checked was the original throttle body for sticking as it has a dual TB set up. The original TB can't close any more.

Any suggestions would be appreciated.

Thanks

Dont know how to edit my sig, so setup is. 265cc injectors, intercooler, mini charger, sequential injection, mini filter on cam cover and below original TB, Dual TB's

I can't see your MSQ at work. Lower spark angle, get back to us. Also, learn to use the shift key and capitalize the first letter of each sentence and proper nouns. We do not tolerate that kind of grammar rape around here, as a safe-place for the like-minded grammarians.

Yes, abuse of the word know doesn't qualify as grammar rape...(see Hustler's sig)

You'll want to start with your IAC settings. Especially your min setting. Decent P and I numbers for PID control are 10 and 80. Small changes to those values should do you well. Unplug your IAC while the motor is running to find out your minimum setting once the engine is warm. If its still 1100rpm, it's not your IAC hurting you. Only posted a couple mins of your warmup so I can't tell what your AFR is once warm. You'll want to keep just under stoich to keep idle stable once you get it under 1000rpm. Also, jacking up the spark at rpms just under slowest idle will help to settle back at the right rpm if it tries to dip.

Post your closed loop PID settings to help us out a bit, or just post the whole msq. Your dashpot adder looks a little bit high, I've got mine at 1.2, but the other settings shown look to be OK. I doubt this is the issue, because your min % open is quite low - I think you've got plenty of range. Try to pull the plug first once warm. If it idles really low, or the car dies, then it's likely your IAC settings, otherwise it's not.

Also post your idle speed targets. 1700 when you start is pretty darn high. I would aim in the 1200rpm range.

Hi Eugene,

Thanks for looking and replying. I will try unplugging the IAC valve and see what happens. My AFR is just under Stoich when idling and I have noticed the rpms drop if I lean it out to 16 ish, but I would prefer to keep it at 14.7. I have attached my msq. I could not attach the msl for some reason.

If you see anything obvious please let me know. I also suspect I might have a boost/vac leak. I took off the air filter on the the inlet to the first throttle body and covered the inlet with my hand making a airtight seal. The revs did not drop! This seems wrong to me. So I briefly tried to pressure test from the air filter, through the charger and intercooler to the inlet manifold but was not successfull. I will try this again on saturday when I get a suitable bung to fit the intercooler pipe work where it joins to the manifold. I dont know how much boost to expect with MP45 and 17% reduction pulley but most I have seen is 148kPa.

Thanks again for helping.

Andrew

It sounds like you do have a vac leak. My guess is - you fix that and you're golden.

I looked over your settings and they all appear to be fine and not far from my own.

Thank you again for looking. A boost leak would be great if I have one and can fix it, as it means more power when its fixed. Its making 199bhp at 6k rpms (injectors are over 100% duty) so when the EV14 arrive in a couple of days I should be over 200bhp. Fingers crossed !

at what idle pwm% are you sitting at when this is happening? It coul dbe that your PID algorithm is not tuned correctly and it's not trying to reach your RPM targets setup in your RPM Targets Curve.

Hi Braineack,

I dont think I understand what you mean when you say 'at what idle pwm% are you sitting at when this is happening'

I hope the attachment is the answer to your question.

Thanks

that actual duty cycle the valve is running at.

you settings suggest it can operate between 13.7 and 80 DC%.

Ok, I get you now. Do you think I should change these?

no. you dont get what im saying at all.

when your idle is sitting at 1100RPM at the lowest, What is the duty cycle it's being driven at?

is it 14%, 15%, 20%, 30%, 35.2%, etc. ????????????????????????


This is like you asking why you cannot shut off your water flow at a sink even though you put your finger over the outlet...and I'm asking is the knob still turned open.

https://www.miataturbo.net/attachmen...1&d=1330703618

This is what a duty cycle is.

Hi Braineack,

Sorry I didn't understand you I am new to this, according to my logs its 2.7 at 1400 rpm.

Also if it helps, sometimes it drops to 1100, then when I blip the throttle it only drops to 1500 or 1600 rpm. Its a bit random.

I also unplugged the IAC when it was warm and idling at 1000rpm, it jumped up to 1400 rpm, then I plugged it back in and it dropped to 1000rpm again. log attached

Thanks

IDLE DUTY CYCLE. NOT INJECTOR.


you understand how an idle valve works right?

okay, on that log, your PWM idle duty starts at 40% where it tapers quick off the 27% where it doesn't ever change again.

basically, your idle code is doing nothing.

Hi Braineack, thanks for looking at my log.

Apologies for mixing up idle duty with injector duty. Looking at your previous replies about turning off the tap, I assumed you meant fuel.

Anyway, I dont know how the idle valve works. I think it adjust fuel/air at different inlet air temps.

How do I adjust my idle code and what do I adjust?

Thanks

Andrew

1st of all I'd suggest a valve freq of 7 not 4

2nd I'd recommend you run an idle valve test when the engine is hot. Use this to set your Idle open/close % values and RPM when valve open/close in the Closed Loop Idle Valve settings and Closed Loop Idle PID settings respectively.

You run the valve test by setting the valve to various values (start with 25) and raise until you note the engine RPM rise, when it does, set it back to just when it doesn't (probably around 30) and then adjut the idle screw to your idle speed (and close the valve and ensure it doesn't drop rpm). Once confirmed and set, this is your closed RPM and closed valve %. Now open the valve to something like 50 or 60 and note the RPM and valve % - this is the open RPM and open %.

Once these values are correct, things should imprve.

G

Hi Grant,

I changed the valve frequency from 4 to 7. No change.

Then I ran the valve test as suggested. When I turned on the valve test the revs jumped to 3000 rpm and would not reduce not matter what value I put into the step. Each time I changed a value the engine blipped a bit as the info was sent to the ECU. Then when I turned off the valve test, the revs still didnt drop. So I switched off the valve test and then the engine and restarted. The revs dropped to 1200-1800 again.

So, I have changed the gauges in tunerstudio (great software) to show the IAC valve and idle PWM%. They do change when the car is idling, but I don't know what changes them. I managed to get a better log of both these during idling and hopefully someone will see a obvious setting to change.

Please look, thanks

Dont bother troubleshooting anything else until you get the idle valve test working. Follow this guide. http://www.mx5nutz.com/forum/index.php?showtopic=46823

If you can't get the test working then everything else is a waste of time as you need to get the values that this test produces.

G

Update,

I got the idle valve test working. I was making the stupid mistake of turning on the test first and then changing the step values. This just sent the idle to 3000 rpm.

So then I changed the values and THEN turned on the test. At the suggested low values of 15-30 the idle remained the same (1350rpm). When I changed it to 90 it jumped to 3000rpm again. I presume this shows the idle valve is working. Also, when I disconnected the plug on the valve, the revs jumps up about 1000rpm.

So, it looks to mee like its working, but just not enough.

One other thing, the idle rpm increases as the engine warms up, ie first start its 1500rpm, then drops steadily as engine warms up to operating temp. Then as the car is driven the idle gradually creeps up (driving through traffic) to 1700rpm

Going to change the injectors in next few days (550cc EV14s). I wonder will this solve it or make it worse?

Anyone any suggestions?

This just proves that you have an air leak. With the idle valve set to close position (anything lower than 30) the car should be running 100% off the idle air screw, in which case you've got it wound so far out it is idling at 1350rpm or you've got a small air leak allowing the car to get air in an uncontrolled way. I'd put money on an air leak, as that would change with temperature as the metal surfaces expand etc. Has the throttle body been apart with the IAC (idle valve) removed? There are small gaskets and some of them can perish and allow lots of air in. Also, there is the warm start valve up on the intake, it may also be at fault.

Again, you've got something wrong as it isn't the megasquirt its the car.

Thanks Grant,

Your reply makes sense, I have not taken the throttle body off or the IAC. I did disconnect some coolant hoses to the warm start valve on the throttle body when changing the injectors. I am getting a mechanic to change to injectors again tomorrow. Maybe if something was disturbed it might be found and put right during the injector instal. If not I'll just drive the car into a lake on boost and look for bubbles !!!:giggle:

Just let the car idle then spray around where you think the leak might be with some carb cleaner. It doesn't take much, just a little squirt. That's how I found my fuel injector vacuum leak. If there is a vacuum leak, spraying the area will cause a change in the idle.

Ok, Finally sorted this when changing my injectors to EV14's

As Grant diagnosed there was a vacuum leak under the warm up valve. My mechanic found it while changing the injectors. The car now idles about 850rpm with the idle screw adjust out. previously it was in all the way.

Just need to retune my VE table now for new injectors and its down to the track on 30th March.

Nice. Glad you got it sorted!