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Old 12-04-2013, 11:50 AM   #1
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Default Help troubleshoot my idle please

I have read a bunch of threads about idle tuning and I have read the MSextra pages and I still don't quite have it nailed down so I could use some help.

When I first start my car up in the morning or after it has been sitting, my car idles at a steady 850-950rpm. The idle will stay at that level during my whole drive (95% of the time) but EVERY time I shut my car off while it is warm the next start results in an idle that makes me sound like an imbecile (which is pretty accurate, but I don't like advertising).

I am not sure if this is the same thing as what people describe as "oscillation" but here is what it is doing: The idle valve will open to about 120 which will rev the car to about 2500-3000 rpm for about two seconds. Then, idle valve closes to more reasonable level and it will hit "fuel cut" for less than a second. Basically it only goes down in rpm as long as it takes to touch 1000'ish rpm then it revs back up to 2500-3000 again.

Usually after about 30 minutes of driving my idle goes back to normal behavior on it's own. I cannot tell what is causing it to start behaving correctly. What is it about a warm car that causes this problem that is not caused by cold? Why does it fix itself?

I did notice that during this whole cycle, my timing never drops below 19 degrees. I am NOT in [IDLE VE] or [IDLE ADVANCE] modes when this happens.

Also, as an experiment today when I got to work I shut the car off and immediately restarted it (causing the idle issues described above). I then forced the idle valve to 27% duty using idle valve test mode which brought the idle down to about 900rpm steady (with approx 10 degrees timing), so this tells me it is not a VE or ADVANCE issue...

I am trying to avoid "wall of text" here but I am not sure what I can show you that will make troubleshooting easier. What do you want me to post?
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Old 12-06-2013, 11:23 AM   #2
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Well, I might as well document my efforts in the hopes that I might help someone else. I started with a map created by someone else here, and rather than do my own tinkering I just ran with it and tried to adjust one variable at a time.

This is clearly a recipie for tears and lamentation.

So, I am going back to square one. First things first, I did a test of my idle valve while warmed up to discover my open and closed duty numbers. I wasn't off by much. I think I will adjust the top and bottom numbers so that it reflects the rpms that I realistically could ever need my idle valve to force, but for now I am leaving them at abou 20% and 72%, which results in RPMs of 650rpm and 3600rpm.

From there, I temporarily changed my idle to "PWM Warmup Only" and adjusted my curve to keep my idle at about 1300rpm down to 900rpm as my car warms up. I no longer have the "seeking" behavior described above.

I will work on making more adjustments as we go on...
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