Won't idle well when warm, but with weird symptoms

[87witmoreboost]

I'm stumped.

My car idled great after rebuild (at about 1000mi now). After rebuild, I set my base timing and the idle was just as it should be. After some time, the idle seemed to hang low after the car warmed up. When I stop after driving, the idle drops to 400-450RPM and then it slowly carries itself up to the 600-700 or whatever it should be (on the order of 30 seconds get up to the 600-700RPM). As soon as I take off and then stop again, it's back down in the 400's - and then repeats process.

I first checked my idle control valve. It wasn't too dirty and I can hear it do it's clicking when key is in ON position. I reasoned that this probably isn't my issue (esp since the idle eventually comes back up?). Next, I again reset my base timing. What's weird is that doing this solved my problem. I was stopping and idle was going right to the happy mid 600RPM range as soon as I pushed the clutch in. After another couple hundred miles, the idle slowly starting decaying to a lower and lower number each time I stopped. Now i'm back in the same boat. I then checked vac leaks with a mityvac and found no leaks.

I don't know what else to try. I have a SAFC2 and that was the last thing I installed, but I soldered it in and did it right. I checked the karman reading right on the unit as a stupidity check and that looks good. TPS also seems to read properly.

Does anyone have any suggestions? I am trying to get the bugs out before I install my fuel system and up the boost on the HKS sport turbo to 15psi.

Help?

 

[mkiiichip]

So timing changed in 1000 miles, and you corrected it. How much did you have to correct? What is it at now?

What are you idle AFR's?

Any oil on the K&N?

 

[CajunKenny]

Any codes?

Was your timing off?

Long shot here; but, if there is a problem with the tension on your timing belt, you could be jumping say.....one tooth at time.....?

Have you verified all of your timing marks?

Dumb scenario here; but, are you tightening your CPS? If it's loose, it'll move around on you.

 

[87witmoreboost]

Thanks guys.

chip, I couldn't tell if it was off because i couldn't read my timing marks at first. Idle AFR's are fine, I believe. I will check tomorrow. Actually, K&N is probably getting pretty dirty.

cajun, no codes (light isn't on...). Timing must have been off if it fixed it when I reset it. Tension could be an issue, but the idle very slowly decays. for example, it was good when reset and then didn't immediately drop in the 400's. It started going to low 600's, then 500's, etc. If it skipped a tooth I would think it would drop all at once and I hear one tooth is significant and would make it run weird. It run's great when not idling.

CPS is/was tight for sure.

 

[CajunKenny]

Codes can be present with out the CEL on.

 

[87witmoreboost]

Codes can be present with out the CEL on.

This is news to me (OBD2 guy, here). I will check codes.

 

[87witmoreboost]

Checked codes and it has none.

After some more driving, the idle dips so low that it stalls now.

The CPS has not moved and the idle has now slowly crept from being the proper 650RPM (after setting base timing) to 400RPM when I push the clutch in. It was a gradual decrease in idle speed over time and approx 500mi.

If i wait it out, it brings itself up to the proper idle speed - it's just the initial idle speed when the clutch is depressed coming to a stop after engine warms up. Again, the idle speed it drops to when I push the clutch in did not just drop to 400RPM on day. It started normal and over the 500mi was slowly decreasing each time I pushed the clutch in.

any other suggestions? It's killin me.

 

[87witmoreboost]

And to add to the mystery, I unhooked the battery and let it sit for a bit and then hooked it back up.

Started the car up and drove 60 miles today. Idle was perfect at first and now drops to about 500-550RPM. Re-setting the battery reset the issue. wtf?

 

[jetjock]

No surprise there. Resetting clears the idle learned value. It also points to the cause of your problem...

 

[ForcedTorque]

It also points to the cause of your problem...

...........Which is???????????????????

I'm assuming (that would make me and jetjock asses) he's saying it's an ECU problem.

 

[whitemike]

...........Which is???????????????????

I'm assuming (that would make me and jetjock asses) he's saying it's an ECU problem.

I love his subtle answers. Makes you work to fix your car.

 

[87witmoreboost]

Yea, I get a kick out of those answers...


It means it learned the wrong value and resetting to "default" makes it know the right value. If it did the opposite (low after reset, learns to idle), I would agree it means that there could be various things wrong and the ECU is learning to correct for the problem. Since resetting does return idle to some default and it idles properly, this means it's learning to idle too low after I drive it.

Why would the car adjust idle to be lower than it should? Is this a hint that my AFM signal is getting distorted/disturbed and telling my ECU the wrong thing?