Odd idle issue
09-28-2016, 08:20 AM
#1
Odd idle issue
I've been having an odd idle issue for quite awhile. The car will periodically idle high. The problem predates replacing the throttle body. It will idle between 1500-2000 RPM. Sometimes, it will do this for several minutes, then suddenly drop to normal idle. It did it again this evening, over an entire 10 mile trip. When I got home, hooked up the scan tool, and IAC position was at 40. After restart, it idled normally, and IAC position was at 0. The throttle definitely isn't sticking, minimum idle airflow was set per FSM, TPS voltage is solid at .54, and both the TPS, and IAC were replaced with new parts when I rebuilt the throttle body.
The problem seemed to start after I replaced the MEMCAL..the car had a MEMCAL for a 5.0 TPI automatic, but the car has an L98. Could I be looking at a bad ECM, bad MEMCAL, badly inserted MEMCAL, or should I be looking at something else? No codes are being set, except for an occasional VSS error, caused by the idle being above 1500 RPM, with the car stationary.
Engine is stock L98, with the exception of the EGR having been deleted, AIR pump deleted, and a T-5 swap. The MEMCAL came from an '88 GTA, 5.7 automatic.
CTS temps were reported at 200 degrees at the time, but I have also seen this odd behavior with the engine cold. There doesn't seem to be any given pattern, I've seen this immediately on startup, and at other times after the engine has been running for awhile, and is completely warm. I'm assuming the reported IAC position with the scantool reflects the commanded position of the IAC pintle, not the actual position of the pintle itself...in other words, I'm assuming I'm not getting a report of a stuck pintle, but for some reason, the ECM is commanding the position at 40.
Suggestions?
The problem seemed to start after I replaced the MEMCAL..the car had a MEMCAL for a 5.0 TPI automatic, but the car has an L98. Could I be looking at a bad ECM, bad MEMCAL, badly inserted MEMCAL, or should I be looking at something else? No codes are being set, except for an occasional VSS error, caused by the idle being above 1500 RPM, with the car stationary.
Engine is stock L98, with the exception of the EGR having been deleted, AIR pump deleted, and a T-5 swap. The MEMCAL came from an '88 GTA, 5.7 automatic.
CTS temps were reported at 200 degrees at the time, but I have also seen this odd behavior with the engine cold. There doesn't seem to be any given pattern, I've seen this immediately on startup, and at other times after the engine has been running for awhile, and is completely warm. I'm assuming the reported IAC position with the scantool reflects the commanded position of the IAC pintle, not the actual position of the pintle itself...in other words, I'm assuming I'm not getting a report of a stuck pintle, but for some reason, the ECM is commanding the position at 40.
Suggestions?
09-28-2016, 11:53 AM
#2
Senior Member
Re: Odd idle issue
Almost impossible to help with this without a log that contains data when the car is running well and when the problem is occurring. If you post a .xdl file be sure to include the .adx, .xdf and the .bin.
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