'97 runaway idle, erratic upshift

[jeffcoslacker]

Some here might remember about a year ago when I had an episode where the car nearly wouldn't stop at a stop sign, and then after stopping I realized the engine was fighting me, idling at almost 2000 RPM.

Then after taking off again, the tranny hesitated on the 1-2 upshift, hanging too long and then shifting harshly. After a few miles, the CEL came on. A little later that evening, the problem went away, and after a restart, the CEL was off once again.

We all speculated, and I was too lazy to read the code and see what happened, and it's been fine until two days ago. Then the same thing happened. I noticed that by shutting the motor off and restarting, or unplugging the TPS and plugging it back in while idling, the idle would settle down until the throttle was opened again.

So today I put a new TPS on, and after a short drive (6-8 miles) to re-learn proper idle strategy, the CEL went off, and all is normal again.

Apparently without a proper reading of throttle position, the ECM can't properly signal the tranny solenoids to upshift, having no way to reference the demand being placed on the motor.

Just thought I'd post it, and try to include all the search words that might help someone with the same problem. Wonder how many tranny shops have sold a "rebuild" based on this malfunction

[tblake]

makes one think...... im glad your problem was just a tps.

[Longknocker]

Originally Posted by jeffcoslacker

Some here might remember about a year ago when I had an episode where the car nearly wouldn't stop at a stop sign, and then after stopping I realized the engine was fighting me, idling at almost 2000 RPM.

Then after taking off again, the tranny hesitated on the 1-2 upshift, hanging too long and then shifting harshly. After a few miles, the CEL came on. A little later that evening, the problem went away, and after a restart, the CEL was off once again.

We all speculated, and I was too lazy to read the code and see what happened, and it's been fine until two days ago. Then the same thing happened. I noticed that by shutting the motor off and restarting, or unplugging the TPS and plugging it back in while idling, the idle would settle down until the throttle was opened again.

So today I put a new TPS on, and after a short drive (6-8 miles) to re-learn proper idle strategy, the CEL went off, and all is normal again.

Apparently without a proper reading of throttle position, the ECM can't properly signal the tranny solenoids to upshift, having no way to reference the demand being placed on the motor.

Just thought I'd post it, and try to include all the search words that might help someone with the same problem. Wonder how many tranny shops have sold a "rebuild" based on this malfunction

I have in the past had the shifting problems (almost like the tranny is slipping)...could it be that that may be my problem also?
It only does it a time or two and i also get the check engine light.

Where is this TPS located so i can check it

[jeffcoslacker]

Originally Posted by Longknocker

I have in the past had the shifting problems (almost like the tranny is slipping)...could it be that that may be my problem also?
It only does it a time or two and i also get the check engine light.

Where is this TPS located so i can check it

The TPS is on the side of the throttle body, on the centerline of the throttle plate (the pivot for the plate goes into the TPS on one side, and to the throttle cable bellcrank on the other side). Two small torx screws hold it on.

Mine had a noticable rattle when shaken, and the part that rotates with the throttle plate shaft had no resistance in it when I tried to turn it.

The effect on the tranny was first gear would hang on too long, and sometimes I had to drop the throttle to get it to upshift (at least it felt that way, I didn't want to over-rev it). Almost exactly like a blown vacuum modulator feels, if you've ever had that experience.

[maxwedge]

A scan would have saved a lot of stuff here.

[occupant]

Throttle position has a lot to do with shift quality. Had it been a high idle and normal shifting I'd have said vehicle speed sensor. Reminds me I need to adjust my throttle cable. Half inch of slack at the throttle body and the gas pedal moves a lot before the car takes off.

[jeffcoslacker]

Originally Posted by maxwedge

A scan would have saved a lot of stuff here.

Too easy . I prefer to think through the problem, and come up with an answer myself, then verify with fault codes to see if I'm on the right track. Sometimes fault codes can be misleading as well, taking you in the wrong direction. When your theory of the problem matches the data, you can be pretty confident you've solved the problem.

In this case, the physical condition of the sensor once I took it off left no doubt it was the problem.

[Longknocker]

Originally Posted by jeffcoslacker

The TPS is on the side of the throttle body, on the centerline of the throttle plate (the pivot for the plate goes into the TPS on one side, and to the throttle cable bellcrank on the other side). Two small torx screws hold it on.

Mine had a noticable rattle when shaken, and the part that rotates with the throttle plate shaft had no resistance in it when I tried to turn it.

The effect on the tranny was first gear would hang on too long, and sometimes I had to drop the throttle to get it to upshift (at least it felt that way, I didn't want to over-rev it). Almost exactly like a blown vacuum modulator feels, if you've ever had that experience.

Thanks again jeffcoslacker,
I am going to have to give that a try.
it sounds simple enough..
Thanks again .

[maxwedge]

Originally Posted by jeffcoslacker

Too easy . I prefer to think through the problem, and come up with an answer myself, then verify with fault codes to see if I'm on the right track. Sometimes fault codes can be misleading as well, taking you in the wrong direction. When your theory of the problem matches the data, you can be pretty confident you've solved the problem.

In this case, the physical condition of the sensor once I took it off left no doubt it was the problem.

Jeff, I meant a full scan so you could see if the tps dropped out, which of course a scope would handle better, not codes alone.

[jeffcoslacker]

Originally Posted by maxwedge

Jeff, I meant a full scan so you could see if the tps dropped out, which of course a scope would handle better, not codes alone.

You're right...I just feel compelled for some reason to try to work out the problem in my head before resorting to diagnostics.

I think it's my way of rebelling against the "black box syndrome", where a system is supposedly unserviceable without specific equipment and knowledge.

It helps me see how the various components relate and work together.

Part of me hates the complexity of modern cars, and wants to believe I can still be effective at repairing them without technical intervention, you know?