Random stall when coming to idle

[-=Jeff=-]

So I have been fighting with a stalling issue. If I am coming to a stop, I usually put it in neutral and coast as I slow down. Every once in a while, the car will stall. Just drop out. It will restart and be fine, usually for the rest of the drive. Just not sure where to look next.

I have:
New O2 sensors
New injectors
New coils
New wires
Plugs are about a year old
New fuel filter
Phil's fuel regulator

I don't seem to have any vacuum leaks
Fuel pressure is solid

Outside of the stall when coming to idle the car runs great

Thoughts on where to look next?

[wfot]

possibly the idle control motor?
could been old
or could just be dirty.
John

[BlackZR1]

What are your IAC counts at idle?
If you are much higher than 10 it suggests your throttle is closed too much and you are relying on the IAC to keep the car from stalling.(Yes the IAC regulates idle speed but the min. throttle hard stop setting should be high enough to keep the car running just below idle rpm target with 0 counts.)
I went through this last month and followed the procedure by XfireZ51 here:
http://zr1.net/forum/showthread.php?p=261060#post261060
Have not had a problem since.

[-=Jeff=-]

IAC was swapped with no change. I did the IAC procedure a couple times. I may need to go through it again but IAC counts are 10 or less fully warm (no AC)

[WARP TEN]

Jeff, you might check with Marc or stop in to see him. I had this stalling problem shortly after he did his 510 package on the '95 and as I recall he just made a minor adjustment to the throttle cable at the front of the engine. I may be wrong, as it was several eyars ago, but that is what I recall.--Bob

[-=Jeff=-]

Thanks Bob,

I have been chatting with him as well.. it happening less now.. time
Will tell

[1991 Corvette ZR-1]

MAP line all clear? This was what stalled mine under the same conditions you?re describing.

[-=Jeff=-]

MAP line all clear? This was what stalled mine under the same conditions you?re describing.

Yes

[Young1]

My car did than when the camshaft position sensor was bad. Check for codes. I think it is 31?

[-=Jeff=-]

My car did than when the camshaft position sensor was bad. Check for codes. I think it is 31?

Yeah no codes present. But interesting issue with cam sensor

[Paul Workman]

I FEEL YOUR PAIN! Sounds familiar. Same thing here (1990 MY) as you described - especially on hot/humid days after fully warmed up AND at higher elevation(!!!!). A few things (including speaking w/ Marc!) seems to have fixed it (at least in IL):


Bumped the idle up (maybe 2-3 hundred rpm)
Re-calibrated my TB, to 5 IAC counts while set at .45VDC (big help!)
Installed (per Marc) the specific NTK O2s (see below) which are suppose to be more responsive.


And... I don't shift to neutral anymore when coasting to a stop: clutch only soas I can let the clutch out if it stalls in order to restart. Also, blipping the throttle right as I shove in the clutch to coast seems to all but alleviate stalling.

I don't know if the problem is isolated to the '90 cars, but stalling is a real PIA because even after I pop the clutch to restart it, when I do get stopped it has to sit still for 4-5 seconds before the idle drops from 2100 to normal - typical anytime the engine is first started on a '90, I'm told. And, if I don't have time to let it idle at a stop before having to go, I will have to do it at some later point or the idle speed will hang at 2100ish RPM while in gear or not. It must be completely stopped and allowed to reset before it will behave normally! :mad: (a PIA to be sure!) (Ami's '91 doesn't need to sit still for the idle to drop to normal, BTW.)

[-=Jeff=-]

Bumped the idle up (maybe 2-3 hundred rpm)
Re-calibrated my TB, to 5 IAC counts while set at .45VDC (big help!)
Installed (per Marc) the specific NTK O2s (see below) which are suppose to be more responsive.


Based off your list:
I have not bumped the idle that much yet, but some and seems to have helped
I need to do a sanity check on the TB Minimum air setting
I also installed the NTK O2s after seeing drop outs in my Bosch O2s on the scanner