Hunting idle caused by bad TPS

[gmbellew]

the idle started to hunt on me a couple months ago. I'm only about a year on the most recent tuneup, so I ran some fuel system cleaner to see if that would help. no change. so I finally got curious enough to plug in the ALDL scanner and watch some data. I noticed that at idle, I could see the TPS voltage randomly vary by up to 0.04v without any actual pedal input. the idle would hunt as the TPS voltage would vary. I couldn't find any loose connections and the TPS was not loose. I happened to have an old spare, swapped it out and all seems good after a couple test drives. Just passing this along in case it helps somebody. I guess the ECM thought I was adding throttle, and making adjustments. but since I wasn't actually opening the throttle, it was making adjustments that it didn't need to make.

 

[Vbb199]

By hunting, do you mean going up randomly? Or like surging back and forth?

 

[gmbellew]

By hunting, do you mean going up randomly? Or like surging back and forth?

It was surging up and down. We'll, really only dropping RPM and then surging back to normal. No more than 50rpm drop. Sometimes it would seem kind of rhythmic and sometimes more random and sometimes it would idle just fine. It wasn't a huge problem yet, but enough that I noticed and finally looked at the data stream. I'd imagine it was only going to get worse as the voltage variation would have undoubtedly gotten bigger as whatever was worn out inside the TPS was going to get more worn out.

 

[Vbb199]

Good to know, my idle would sometimes do weird stuff. I guess that could be why.

 

[gmbellew]

Good to know, my idle would sometimes do weird stuff. I guess that could be why.

I was honestly surprised that such small voltage changes in TPS would cause it. I actually noticed the small voltage changes a couple weeks ago and just shrugged it off. Then remembered I had a spare TPS in the parts tub and thought I'd check it out and see if that was the issue while i was doing a LOF. Turns out the TPS was causing the idle issue. Be really hard to diagnose something like that without a scanner or ALDLDroid....

 

[fast 99]

Know there are other options but a red brick or Tech 1 scanner is something to consider buying. They are obsolete and relatively cheap today.

 

[gmbellew]

Know there are other options but a red brick or Tech 1 scanner is something to consider buying. They are obsolete and relatively cheap today.

I've thought about also getting a tech1. But I was always unsure of exactly what I needed to get for it to work. It does have a some more capability than ALDLDroid.....

 

[fast 99]

I've thought about also getting a tech1. But I was always unsure of exactly what I needed to get for it to work. It does have a some more capability than ALDLDroid.....

Don't know. However the Tech 1 does have more capability/data than the snap on red brick on GM vehicles. Biggest problem with either of those is the condition of the leads.