Wierd warm start problem
Thread Starter
Advanced
Joined: Jun 2001
Posts: 89
Likes: 0
From: Chicago
Wierd warm start problem
Hi everyone,
I have not posted on here in quite some time, so I feel guilty coming on with a wierd problem, but I hope someone can help me because so far the dealer's mechanics are stuck on this one.
For many months my 91 C2 has had a problem where, occasionally on a warm start, the check engine light will come on and the car will hunt for idle and hesitate very, very badly on accelleration. The faster you try to accelerate, the worse the hesitation. Occasionally, it will backfire. It will do that for a few minutes of driving, then, just when it is hesitating at its worse, it will suddenly clear up and run fine until the next time I turn it off. It is always on a warm start (unless I turn it off with the problem happening, then it will happen on start up even the next day). It always clears up in a few minutes.
It was happening only occasionally, so I didn't bring it in until now because I thought they wouldn't be able to recreate it, but now it is happening most of the time. The check engine code reads to the mass air flow sensor.
Any thoughts? Thanks for your help.
-Tom
I have not posted on here in quite some time, so I feel guilty coming on with a wierd problem, but I hope someone can help me because so far the dealer's mechanics are stuck on this one.
For many months my 91 C2 has had a problem where, occasionally on a warm start, the check engine light will come on and the car will hunt for idle and hesitate very, very badly on accelleration. The faster you try to accelerate, the worse the hesitation. Occasionally, it will backfire. It will do that for a few minutes of driving, then, just when it is hesitating at its worse, it will suddenly clear up and run fine until the next time I turn it off. It is always on a warm start (unless I turn it off with the problem happening, then it will happen on start up even the next day). It always clears up in a few minutes.
It was happening only occasionally, so I didn't bring it in until now because I thought they wouldn't be able to recreate it, but now it is happening most of the time. The check engine code reads to the mass air flow sensor.
Any thoughts? Thanks for your help.
-Tom
Race Car
Joined: Nov 2001
Posts: 4,140
Likes: 1
From: Surrey, UK
Don't you believe the check engine code? I would expect a problem with the air flow sensor to cause the kind of running problems you describe - and if the diagnostics say it is that, then it's a good place to start.
One thing worth mentioning - I believe there was some kind of update to the connector on the air flow sensor (I'm sure Adrian mentioned it once when I had running problems). Think there is supposed to be a black dot on the connector if it's been done. It's worth checking this - maybe you are having problems at this connector. Failing that - I would be inclined to take the air flow sensor off and give it a good clean out.
One thing worth mentioning - I believe there was some kind of update to the connector on the air flow sensor (I'm sure Adrian mentioned it once when I had running problems). Think there is supposed to be a black dot on the connector if it's been done. It's worth checking this - maybe you are having problems at this connector. Failing that - I would be inclined to take the air flow sensor off and give it a good clean out.
Thread Starter
Advanced
Joined: Jun 2001
Posts: 89
Likes: 0
From: Chicago
The symptoms don't fit an air flow sensor failure. Just to be sure, the mechanic took a sensor off another car today and put it in, and the problem persists. They're on their third day with the car now, and they are still stumped. Fortunately, business is a little slow so they are looking at it and very kindly not charging me for most of the diagnostic time.
The only other clue is that the starter is also failing and, on starting, the tach often jumps up to 3k for a second. It's possible that the difference between this tach reading and the idle position of the air flow sensor is causing the DME to trigger a sensor fault.
Anyway, I was just hoping someone else might have seen something like this, but its beginning to look like it is a unique gremlin. Thanks anyway.
The only other clue is that the starter is also failing and, on starting, the tach often jumps up to 3k for a second. It's possible that the difference between this tach reading and the idle position of the air flow sensor is causing the DME to trigger a sensor fault.
Anyway, I was just hoping someone else might have seen something like this, but its beginning to look like it is a unique gremlin. Thanks anyway.
Thread Starter
Advanced
Joined: Jun 2001
Posts: 89
Likes: 0
From: Chicago
Well, it looks like the problem was the starter. I didn't mention at first that my starter would sometimes kick out because I didn't think the two problems were related or always occured together. But replacing the starter seems to have fixed the problem. Somehow, the starter was doing something to cause the tach to jump up and make the cpu think the car was doing 3k when the air flow meter was at idle. So it would tigger a fault against the air flow meter and go into a limp home mode. After awhile, it would correct itself. At least that's the theory.
Wierd. But easily fixed as it turns out. At least pending driving it this weekend enough to confirm that the problem is really gone.
Wierd. But easily fixed as it turns out. At least pending driving it this weekend enough to confirm that the problem is really gone.
