need help with poor idle
Thread Starter
Le Mans Master
Joined: Apr 2003
Posts: 6,059
Likes: 2
From: Texas
need help with poor idle
My 96 LT1 has been idleing horribly recently....it seems like it is idleing way too low causing the entire car to shake, but once i give it some gas it seems to smoothen out...I have replaced the IAC and it seems to not have done anything to fix it. The car does not miss or hesitate at higher RPMs, just at idle it shakes horribly. This also happens when the car is warmed up and not when it is cold...what could be doing this?
Melting Slicks
Joined: Jul 2000
Posts: 2,107
Likes: 14
From: Lancaster PA
How old is your OPTI? My 94 idled rough too at higher temps and I just replaced the OPTI and it idles like a new one. When I took the old unit apart and saw how rusty it was inside it is hard to believe it ran at all.
btw the brakes that you sold me are great. Craig
btw the brakes that you sold me are great. Craig
Melting Slicks
Joined: Oct 2004
Posts: 2,510
Likes: 4
From: Austin Texas
For months, I was chasing a Hot engine idle problem exactly as you describe on my -95 LT1. I changed out the TPS and IAC, and I still had a stumbling idle when engine hot. I replaced Fuel Filter, still had idle problem. Then I replaced both my O2 sensors and BLAM! Problem solved. 
Just so I don't get flamed for blindly replacing parts, I did check my error codes and had H-22, H-44 and H-64...which is TPS, lft O2 sensor and rht O2 sensor respectively..
Also, when engine is cold, O2 sensors are ignored by PCM, and engine is in Open Loop. O2 sensors come into "AF ratio" equation only after they have reached a certain temp.(ie very hot)
If your O2 sensors are bad, here is a thread I started asking about tips and procedures for replacement...
http://forums.corvetteforum.com/show....php?t=1005664
Just so I don't get flamed for blindly replacing parts, I did check my error codes and had H-22, H-44 and H-64...which is TPS, lft O2 sensor and rht O2 sensor respectively..
Also, when engine is cold, O2 sensors are ignored by PCM, and engine is in Open Loop. O2 sensors come into "AF ratio" equation only after they have reached a certain temp.(ie very hot)
If your O2 sensors are bad, here is a thread I started asking about tips and procedures for replacement...
http://forums.corvetteforum.com/show....php?t=1005664
Last edited by MikeC4; Feb 5, 2005 at 08:32 PM.
Thread Starter
Le Mans Master
Joined: Apr 2003
Posts: 6,059
Likes: 2
From: Texas
Originally Posted by MikeC4
For months, I was chasing a Hot engine idle problem exactly as you describe on my -95 LT1. I changed out the TPS and IAC, and I still had a stumbling idle when engine hot. I replaced Fuel Filter, still had idle problem. Then I replaced both my O2 sensors and BLAM! Problem solved.
Just so I don't get flamed for blindly replacing parts, I did check my error codes and had H-22, H-44 and H-64...which is TPS, lft O2 sensor and rht O2 sensor respectively..
Also, when engine is cold, O2 sensors are ignored by PCM, and engine is in Open Loop. O2 sensors come into "AF ratio" equation only after they have reached a certain temp.(ie very hot)
If your O2 sensors are bad, here is a thread I started asking about tips and procedures for replacement...
http://forums.corvetteforum.com/show....php?t=1005664
Just so I don't get flamed for blindly replacing parts, I did check my error codes and had H-22, H-44 and H-64...which is TPS, lft O2 sensor and rht O2 sensor respectively..
Also, when engine is cold, O2 sensors are ignored by PCM, and engine is in Open Loop. O2 sensors come into "AF ratio" equation only after they have reached a certain temp.(ie very hot)
If your O2 sensors are bad, here is a thread I started asking about tips and procedures for replacement...
http://forums.corvetteforum.com/show....php?t=1005664
thats the kind of response i was looking for....2 of my oxygen sensors are not working correctly...on one side before the cat and on the other side after the cat....i thought that they were causing the problem, but i wanted to see what others would say with the symptoms i am having without saying what I knew was wrong to confirm it...thanks
Last edited by OrthoAggie; Feb 5, 2005 at 09:01 PM.
Thread Starter
Le Mans Master
Joined: Apr 2003
Posts: 6,059
Likes: 2
From: Texas
Originally Posted by CF6873
How old is your OPTI? My 94 idled rough too at higher temps and I just replaced the OPTI and it idles like a new one. When I took the old unit apart and saw how rusty it was inside it is hard to believe it ran at all.
btw the brakes that you sold me are great. Craig
btw the brakes that you sold me are great. Craig
Instructor
Joined: Jan 2004
Posts: 154
Likes: 0
From: Katy TX
I had a similiar issue as well. I replaced O2 sensors, and still after it was warm, when i would sit at a stop light, or idle down, it would shake pretty bad, I would have to throw it in nuetral, (i have an auto) and have to rev it to keep it running. IT was a very simple fix, I had some of the wiring harness that had touched the engine, and had bare wiring just out in the open, I wrapped up the wiring, and no problems since. Hope this helps.
Thread Starter
Le Mans Master
Joined: Apr 2003
Posts: 6,059
Likes: 2
From: Texas
Originally Posted by BillSF49
I had a similiar issue as well. I replaced O2 sensors, and still after it was warm, when i would sit at a stop light, or idle down, it would shake pretty bad, I would have to throw it in nuetral, (i have an auto) and have to rev it to keep it running. IT was a very simple fix, I had some of the wiring harness that had touched the engine, and had bare wiring just out in the open, I wrapped up the wiring, and no problems since. Hope this helps.
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Melting Slicks
Joined: Oct 2004
Posts: 2,510
Likes: 4
From: Austin Texas
Originally Posted by deiaggie
thats the kind of response i was looking for....2 of my oxygen sensors are not working correctly...on one side before the cat and on the other side after the cat....i thought that they were causing the problem, but i wanted to see what others would say with the symptoms i am having without saying what I knew was wrong to confirm it...thanks
Also, please check this with other CF members, but I have heard that the O2 sensors located 'after' the cats, do not affect AF ratio?? But of course this leads to the question, what the heck is it there for then??? DOH
Thread Starter
Le Mans Master
Joined: Apr 2003
Posts: 6,059
Likes: 2
From: Texas
Originally Posted by MikeC4
deiaggie, I am curious, does your '96 have 4 O2 sensors ? That is, 2 before and 2 after your cats? My '95 has 2 total, both before the cats.
Also, please check this with other CF members, but I have heard that the O2 sensors located 'after' the cats, do not affect AF ratio?? But of course this leads to the question, what the heck is it there for then??? DOH
Also, please check this with other CF members, but I have heard that the O2 sensors located 'after' the cats, do not affect AF ratio?? But of course this leads to the question, what the heck is it there for then??? DOH
