Idles good sometimes, sometimes not at all
Thread Starter
Instructor
Joined: May 2007
Posts: 109
Likes: 0
From: Ostersund (Sweden)
Idles good sometimes, sometimes not at all
I've found many threads about Idle but not with this particular problem, or maybe I just can't recognize any similarities with the other threads.
I've got a 1991 Automatic.
Usually when I start the engine (cold or warm) it starts right up and idles really good.
But sometimes (more frequently now than before) it fails to hold the idle speed and just dies on me. It still doesn't matter if it's hot or cold. I can fix it by slowly letting go of the accelerator, really really nice and slow and let it land on idle speed.
Where should I start to look?
I've got a 1991 Automatic.
Usually when I start the engine (cold or warm) it starts right up and idles really good.
But sometimes (more frequently now than before) it fails to hold the idle speed and just dies on me. It still doesn't matter if it's hot or cold. I can fix it by slowly letting go of the accelerator, really really nice and slow and let it land on idle speed.
Where should I start to look?
Pro
Joined: Mar 2007
Posts: 526
Likes: 1
From: San Angelo Texas
I don't suppose you have a scan tool do you? I would start simple and look for something obvious like a loose connection at one of the various sensors, or a cracked vacuum line. From what little you have mentioned it screams bad sensor somewhere to me. A scan tool would be really good for finding something like that. I wish I could be more help but I wanted to get my .02 in before you started throwing serious money at a problem. Good luck. Oh, and give what wiring you can see a once over and see if something is kinked, insulation is cut, or something is burned.
Burning Brakes
Joined: Apr 2004
Posts: 762
Likes: 2
From: Huntington ma
Most likely a dying IAC, although that's not Necessarily the problem.
Could just need a good cleaning, could be the ECM not telling the IAC to do what it should because of goofy sensor data getting to the ECM (TPS maybe, or the signal from the ignition, or the Coolant temp, or...)
Start with a scan tool, watching the sensor signals when it acts up. You will also be able to see what the ECM is commanding the IAC position to be, and if That is normal and it won't idle, then the IAC itself is your suspect..
Could also be a vacuum leak thing - maybe an EGR valve problem (sometimes not closing), etc. Lots of interesting possibilities
Could just need a good cleaning, could be the ECM not telling the IAC to do what it should because of goofy sensor data getting to the ECM (TPS maybe, or the signal from the ignition, or the Coolant temp, or...)
Start with a scan tool, watching the sensor signals when it acts up. You will also be able to see what the ECM is commanding the IAC position to be, and if That is normal and it won't idle, then the IAC itself is your suspect..
Could also be a vacuum leak thing - maybe an EGR valve problem (sometimes not closing), etc. Lots of interesting possibilities
Le Mans Master
Joined: Aug 2007
Posts: 8,735
Likes: 412
From: WV
Most likely a dying IAC, although that's not Necessarily the problem.
Could just need a good cleaning, could be the ECM not telling the IAC to do what it should because of goofy sensor data getting to the ECM (TPS maybe, or the signal from the ignition, or the Coolant temp, or...)
Start with a scan tool, watching the sensor signals when it acts up. You will also be able to see what the ECM is commanding the IAC position to be, and if That is normal and it won't idle, then the IAC itself is your suspect..
Could also be a vacuum leak thing - maybe an EGR valve problem (sometimes not closing), etc. Lots of interesting possibilities
Could just need a good cleaning, could be the ECM not telling the IAC to do what it should because of goofy sensor data getting to the ECM (TPS maybe, or the signal from the ignition, or the Coolant temp, or...)
Start with a scan tool, watching the sensor signals when it acts up. You will also be able to see what the ECM is commanding the IAC position to be, and if That is normal and it won't idle, then the IAC itself is your suspect..
Could also be a vacuum leak thing - maybe an EGR valve problem (sometimes not closing), etc. Lots of interesting possibilities
Sounds like the IAC is hanging up sometimes..Its probably dirty or going bad. If you can get a scan tool this is your best bet.If you have a FSM it will tell you how to check the IAC for proper operation..
Thread Starter
Instructor
Joined: May 2007
Posts: 109
Likes: 0
From: Ostersund (Sweden)
Thanks guys!
I will check that IAC and all the cables around it.
Someone mentioned the EGR valve? I got error code H32 but my novice guess it's because I emptied all the three cathalytic converters?
The error is so intermittent it's hard to find it. The last days I've had NO problems at all..
I don't have a scan tool or FSM so have to do it the hard way i guess :/
I will check that IAC and all the cables around it.
Someone mentioned the EGR valve? I got error code H32 but my novice guess it's because I emptied all the three cathalytic converters?
The error is so intermittent it's hard to find it. The last days I've had NO problems at all..
I don't have a scan tool or FSM so have to do it the hard way i guess :/
