K2500HD Idle Issues...

[ErikSS]

Is it possible the alternator is causing some of these other problems? I've seen over charging as well as field problems do some strange things.

[bartonmd]

Is it possible the alternator is causing some of these other problems? I've seen over charging as well as field problems do some strange things.

No, this just started, today. It may have had something to do with someone (allegedly) hitting it with a rubber mallet to get it back into its mounts after changing the intake gaskets.

Mike

[dvanbramer88]

Is it possible the alternator is causing some of these other problems? I've seen over charging as well as field problems do some strange things.

No, this just started, today. It may have had something to do with someone (allegedly) hitting it with a rubber mallet to get it back into its mounts after changing the intake gaskets.

Mike

I ruined an alternator that way once.

[KE7WOX]

Is it possible the alternator is causing some of these other problems? I've seen over charging as well as field problems do some strange things.

No, this just started, today. It may have had something to do with someone (allegedly) hitting it with a rubber mallet to get it back into its mounts after changing the intake gaskets.

Mike

That could have easily been a ....factory... defect.

[bartonmd]

Well, it's not the alternator.

It's not the clutch switch.

The symptoms kind of fit a stuck open EGR, but I removed mine and it moves freely and spring returns. To be safe, though, I cut a thin piece of sheetmetal and sandwiched it between the EGR and the base, to totally block the flow. Still the same thing. Not the EGR...

Took my Dad for a ride this morning, showing the logging software and what it is doing. He agreed that it is the strangest thing he's ever seen a vehicle do, and that it may be something in the ECM, or some other little oddball thing that nobody's thought of... After the snow this coming week, I'm going to take it to the dealer and get it done to me, I guess...

Mike

[ErikSS]

I sure wish I had more ideas for you. The only thing left on my mind is upstream O2 sensors. Typically they throw codes though. I hope the dealership gets it right for you. My dislike for dealerships has been escilated almost to hatred now. haha

[bartonmd]

I sure wish I had more ideas for you. The only thing left on my mind is upstream O2 sensors. Typically they throw codes though. I hope the dealership gets it right for you. My dislike for dealerships has been escilated almost to hatred now. haha

The waveform from the O2 sensors looks like it should, and yeah, they normally throw codes if they're bad enough to stop it from running right.

It's just really, really strange that it idles fine while sitting still, but bobbles around between 300 and 400rpm coasting with the clutch in (or in neutral with the clutch in or out) while you're moving, for as long as you're moving, in closed loop or open loop, and then goes right up to a steady 600rpm the instant you come to a stop. Once it's warmed up, it comes back to idle just fine from a blip, but when you're coasting, blipping comes back down to the 300-400rpm where it was, before. It'll stay at that rpm even if you coast for 1/2 mile, then right back up to 600 when you stop. It also sometimes catches itself at 600 on the way down, for a couple seconds, then drops to 300-400 until you come to a complete stop. It is really, really strange!

I also hope the dealership gets it right! I've got a buddy who works at a dealer, and who is good, who I hope will be the one to look at it.

Mike

[bartonmd]

OK, I never would have gotten this one... $900 at the dealer later, it's fixed. It was the throttle body.

Apparently, in the throttle sticking (which mine wasn't doing, BTW) TSB, there was a voltage spec saying that if the TPS voltage at closed throttle was more than 0.61V, don't do the TSB, and replace the throttle body. Mine was 0.63V. From what my buddy (dealer mechanic) was saying, it would seem that if it's above .61V, the computer thinks you are slightly on the gas when it's moving, and closes the IAC.

I didn't think it really fit, because that's a wear issue and this happened all at once, but this happened 1 heat cycle after I cleaned a bunch of grounds. The only thing I can think of is that the high resistance grounds (which ended up causing an ABS light, which is what caused me to clean them) were taking away a couple tenths of a volt from the reference voltage in the computer, so everything was OK. I cleaned those grounds, then BAM, it sees a problem that's been developing for a while...

Mike

[RyansTBLS]

Glad to hear it's running good again!

[dvanbramer88]

OK, I never would have gotten this one... $900 at the dealer later, it's fixed. It was the throttle body.

Did they include the lube?


at least it's fixed right now and everything is correct again.

[bartonmd]

OK, I never would have gotten this one... $900 at the dealer later, it's fixed. It was the throttle body.

Did they include the lube?


at least it's fixed right now and everything is correct again.

$600 was the part (all the $150-$250 aftermarket parts say for auto trans only, and if we thought it was the problem, I wasn't going to also test if an auto trans TB worked on a manual trans truck, and guess which was the reason that something didn't work), which is discontinued, and I got 1 of 2 left in the country, that were in stock at other dealers. I only got charged for 2.5 hours of labor, even though he had almost 4 in it (buddy I've known for 10 years), with test drives and such, over a couple days.

Mike

[dvanbramer88]

Dang, that's an expensive part. Well I guess than, it is what it is. It's good you got the part you needed.

[bartonmd]

Dang, that's an expensive part. Well I guess than, it is what it is. It's good you got the part you needed.

Yeah, but looking at the old part this morning, the new one came with the TPS and the IAC already attached to it, which are, even for aftermarket ones, $150 in parts (which I had already replaced, as it happens).

Mike

[v7guy]

What a peculiar problem. Never ever would have guessed that.
Don't post this on GMTnation or they're all going to start raving about good clean grounds causing massive problems on GM vehicles.

[TBYODA]

Don't post this on GMTnation or they're all going to start raving about good clean grounds causing massive problems on GM vehicles.

hahahahahahahah

[bartonmd]

What a peculiar problem. Never ever would have guessed that.
Don't post this on GMTnation or they're all going to start raving about good clean grounds causing massive problems on GM vehicles.

I LOL'd!

Mike

[KE7WOX]

What a peculiar problem. Never ever would have guessed that.
Don't post this on GMTnation or they're all going to start raving about good clean grounds causing massive problems on GM vehicles.

I made this meme a couple of months back, after replacing my dahsboard stepper motors, and in the process throwing the rear wiper switch off position.

[bartonmd]

Interestingly enough, messing with the old TB, there's probably close to 1/16" of play in it when you hold the throttle open and move it back and forth. So it would seem that, yes, the throttle body was actually "worn out."

Mike