Problem: Fast idle Conditions: Cold start, hot start, any time. Problem: When Cold - Engine rev’s upto ~4k rpm upon startup and hangs there a few secs (2-3). Then slowly drops to ~1.5-1.8k idle. When hot - Engine rev’s to ~2.5k and idles ~1.2-1.5k rpm. What we’ve done so far: Check plugs & wires, Replaced downstream O2 sensor (had a CEL for it), replaced fuel filter, checked and replaced IAC valve, replaced TPS sensor (had a CEL for it), had an independant shop look at it and say “We dont know”. Need to fix by: December - for NYS Inspection reasons.
Don’t want to take it to a GM dealership and pay $90/hr unless we have to.
Only other idea I have is a reflash of the BCM/ECM :crap:
hrmmmm…IAC usually makes the car want to die rather than high rpm type stuff. it sounds like something with the warm-up cycle might be wrong. if the warm-up idle air adder function is wrong it would make sense. id have the dealer check the program on the ECU. i know on my car with my program you can set how high the rpms would go to warm up and how long before they settle down to normal idle.
I drove this thing around yesterday because my truck was on loan… when You first start it up it rev’s nice and high and You can actually hear the IAC “blow off” and try to work. This is new.
Yea, i was thinking that something could be amiss in the Warm-Up Enrichment side of the ECU.
Possibly the CTS might be toast too, but the gauge works and there are no othre symptoms.
A big vacuum leak would cause the car to stumble and almost want to die. His revs high. Also CTS stand for Coolant Temp Sensor. Not sure what exactly could be causing this. Wish I could help more but i’d have to plug in my Scan tool to figure out what the car is doing. Have someone look at it, thats all I can say. Dont just keep throwing parts at it.
how bout the wiring to the intake air temp sensor theres a bulliten fo the harness bieng to short and sensor reading inop that may have something to do with it check it out
I had these problems on few i had worked on…lets see if i can dig out the archives of the mind from my GM days LOL
On the 2.4 the breather hose from the oil serperator went into the underside of the throttle body bonnet. The significance of this is that hot oil vapors from the seperator had a tendancy to coke up in the throttle body and cause sticking. Depending on your wifes driving habits it is possible that this has caused and issue with the throttle plate sticking open enough to cause a high idle. I have seen this happen on a few cars. This is most likely the cause of the TPS code as I have personally never seen a TPS sensor go bad on these cars EVER. Any time you get odd issues with driveability in this area it is usually wiring.
The reason i say that this may be the source of the code without looking at the car is based on the fact that i have not seen any issues with these sensors, and on top of that if the throttle was cracked at start up this may cause the PCM to read this as higher than normal throttle position for all of the other sensor parameters and then set the code because the sensor is out of range.
That or the IAC as mentioned trying to do its job it is possible that the IAC is carboned up to the point that it cannot meter air properly anymore.
I have not seen the car nor looked into any of this so they are all educated guesses, take them for what they are worth.
On a side note, I miss working and diagnosing GM vehicles…it was a real challenge and kept you on your toes with everything they changed and how often they changed product…it will be sad to see them gone if they dont get their shit together.
also the 02 and tps are false codes caused by high rpm from vac leak but normal tps voltage as well as lean condition piked up by o2’s, the pcm is confused