Rough idle with AC on and in gear

[jimmackey11]

I've been searching through this awesome site for weeks trying to get to the bottom of my rough idling and vibration through the steering column in my 2004 Envoy 4.2 and have tried a number of things already and am still having issues. I must be overlooking some things. The Envoy has 145,000 and I've kept up with the maintenance on it over the years. If anyone has any more ideas on what to do next I'd greatly appreciate it. Here's the list of things already taken care of in the last couple of weeks:

- replaced the throttle body (new OEM part not a rebuilt part)
- replaced the MAP and air temp sensor
- changed the spark plugs (AC Delco 41-103)
- replaced all 6 coils after 3 went bad
- did the Seafoam in the brake vacuum line (twice) and in the gas tank
- replaced the fuel filter
- reset the PCM by disconnecting the battery for over 30 minutes after the TB replacement and again after the new spark plugs
- had the engine mounts replaced but they weren't the OEM part
- took it to the dealer to see if the PCM needed an update and they told me no - they told me to replace the transmission mount
- no codes or CEL ever
- replaced the upstream O2 sensor
- replaced the alternator a couple of months ago when it went bad
- just replaced the tensioner pulley and serpentine belt when the pulley started to go

The symptoms are kinda similar to others I've read but a little different too. Without the AC on it runs smooth and seemingly perfect. As soon as I turn on the AC the rough idle starts and so does the vibration but its only noticeable when in gear and stopped. When the car is still "cold" the idle RPMs run at about 700 but after the car gets to temp the idle (in gear and at stopped at a light) seems to drop to 500 but waffles a bit to 650 then back to 550. The lower the RPMs go the worse the vibration gets.

So I need help (in more ways then one but that's for a different forum!) trying to figure what I've overlooked. I've read a lot about the camshaft actuator solenoid and I guess that's the next thing to try? I'd love any and all thoughts or ideas. Thanks, Jim.

 

[The_Roadie]

- had the engine mounts replaced but they weren't the OEM part

Welcome!

Assuming it's a 10 Hz rotational vibration, and not mostly erratic (up and down changes you can see on the tach or a scan tool) idle RPM, then your motor mounts need to be changed again. Aftermarket mounts are reportedly too stiff, which is normally a good thing, but our hydraulic mounts are tuned to stop this specific vibration.

The huge clue is that it goes away in neutral.

If it's an up/down RPM change, then I'd replace the CPAS with an AC Delco.

 

[jimmackey11]

I figured those mounts might be part of the problem - crap. Let that be a good lesson for myself and anyone else out there trying to save a few bucks and then it's just not worth it! And the camshaft actuator I just ordered. What exactly does that camshaft solenoid thing do that affects the idle so much? Not doubting you here, just trying to learn something.

 

[jimmackey11]

Oh, and the part about the dealer recommending to replace the transmission mount - is that something that is common? I don't see many posts or comments about that part - just wondering if its worth it or it was just dealerspeak to jack up the total? There used to be a Roadie on the Trailvoy site that always had great info - any relation?

 

[The_Roadie]

Oh, and the part about the dealer recommending to replace the transmission mount - is that something that is common? I don't see many posts or comments about that part - just wondering if its worth it or it was just dealerspeak to jack up the total?

They're guessing. Poorly. I think 10 people change their motor mounts for each owner who also does the tranny mount. Never had any firm proof of a connection of vibration to the tranny mount. Some members found pebbles in a slot in the tranny mount and vibration went away when they pried out the rocks.

There used to be a Roadie on the Trailvoy site that always had great info - any relation?

Nah, never heard of the bum.

No seriously, I'm the same guy. When the ENTIRE moderator and admin team at Trailvoy ran a jailbreak in Dec 2011 and started this site as a protest against the greedy corporate third owners of Trailvoy (Vertical Scope, an evil Toronto corporation), they initially listed us as all BANNED. But that got members asking the hard questions like YOU BANNED THE ROADIE? ARE YOU NUTS? WHERE DID HE GO?!? So they changed most of our tags to read "No longer here..." as if I was DEAD or something. Told you they were evil. I'm old, but not dead.

I figured those mounts might be part of the problem - crap. Let that be a good lesson for myself and anyone else out there trying to save a few bucks and then it's just not worth it!

Exactly the point behind my avatar caption.

And the camshaft actuator I just ordered. What exactly does that camshaft solenoid thing do that affects the idle so much? Not doubting you here, just trying to learn something.

GM's Variable Valve Timing | Diagnostic News

 

[jimmackey11]

Yeah, "No longer with us" is a bit dead sounding - glad you're still around!

Anyway, a little confused on the location of the CPAS on the 2004 Envoy 4.2. I've looked at some videos and posts about having to remove the belt, drop the PS to get to it, but I saw a photo that showed the CPAS on top of the motor just behind the oil cap (see below). Is the red arrow showing the CPAS? ANd the blue is the sensor?
View attachment 29942

 

[The_Roadie]

Exactly.

 

[jimmackey11]

Hey Roadie - another odd question - have you ever seen or heard of anyone having idle issues while in park and closing the power windows? Mine has been doing it for a while now and I never thought to ask before. It's sporadic so it doesn't happen every time but every now and then the engine feels like it is just about to stall. Seems to happen after the window gets to the top so it's stopped moving up and just before you release the window up button.

Replaced the CPAS today and I have to admit that was easier than I initially first thought. The engine is running so much better! The old one "looked" ok - no obvious blockage or damaged screens like I've seen in other posts so it must have been going bad.

I really do appreciate all the great insight from you!

 

[The_Roadie]

When the window gets to the top or bottom, the current goes WAY up. If the battery can't keep up, then the alternator is tasked with supplying the current. A marginal alternator will put extra load on the engine just like a cycling AC compressor. If you have good idle RPM behavior when the AC cycles on and off, then your throttle body is adequately clean and that's not your problem. I'd take the battery and alternator to get checked out under load at the parts store.

 

[jimmackey11]

You were right! The battery actually died this morning which wasn't a great way to start a Monday. Had the alternator tested just be safe and it was perfect. Kind of strange that yesterday I got stuck in traffic for about 45 minutes (actually was stopped on the highway for 45 minutes due to a wreck) and the Envoy just about stalled out after about 20 minutes of sitting with the AC on. The SES light came on for a split second but the truck didn't stall out. It was ok after that but it started kind of weird last night . Could the battery problem have caused the near stall out? Or do I have something else going on that I need to figure?

 

[The_Roadie]

I almost always ask posters with electrical issues what they found when they put their voltmeter on the battery. I seem t have forgotten to do that in this case. So what *did* your meter tell you about your battery?

Depending on what was wrong with the battery, it could have easily been loading down the alternator, lowering the voltage as it tried to boil over and explode in the engine compartment. Lowered voltage has all sorts of bad and mysterious side effects.

 

[jimmackey11]

On the battery, the auto parts place tested the battery so I didn't put a volt meter to it myself. The guy said the battery wasn't charged and showed it had something like 620 amps and 600 was the minimum to be considered "good". So he said he would charge the battery and that device would also run a test on the battery while charging. He came back in five minutes and said the battery failed and needed to be replaced. Then he tested the alternator and it was 14 volts steady (with the AC on).

 

[jimmackey11]

Roadie - a question I meant to ask the other day - the new CPAS came with what I can only describe as a very thing "spring" over each of the three screens. Is that something that needs to come off the CPAS before it gets installed or is that what the new ones look like? I can't find any pictures on the site where people show them on there. I installed an aftermarket one to replace the bad original one and ordered one from GM parts. The aftermarket one did not have them but this new GM one does, and I thought maybe they put this "spring" over the screens for shipping purposes. Just want to check before I install the GM one.

 

[The_Roadie]

Please post a picture of yours. I think it's normal. Lots of people find missing screens when they take the old ones off!

 

[jimmackey11]

Here is the new CPAS with the "spring" things over the screens

View attachment 30114.jpg]

 

[The_Roadie]

Man, that's unique in my experience but I'd leave them on because of the occasional missing screen problem. Must be GM's response.

 

[jimmackey11]

Seems as if I still have an occasional almost stall for some reason. It's kinda driving me nuts! The last couple of days it's almost stalled right after I turned the AC off but the car was still idling in park. Once in a while I still feel a very slight hesitation accelerating from a stop with the car in gear. Not the end of the world but what would be the next things to check?

 

[jimmackey11]

The Envoy just about stalled out this morning in park right after I turned the AC off. Still randomly hesitates a split second accelerating from a red light stop but not every time. Anyone got any ideas on what to look into next?

 

[The_Roadie]

Not sure. Find a mechanic with a GM Tech II tool and have them look for fuel injector pulse widths and run the CPAS through its paces. I see you already did the Seafoam. Maybe injectors?

 

[jimmackey11]

Not sure. Find a mechanic with a GM Tech II tool and have them look for fuel injector pulse widths and run the CPAS through its paces. I see you already did the Seafoam. Maybe injectors?

Here's what the Scan XL report shows on the fuel injectors:
Injector Value Units Min Avg Max
1 2.7 ms 2.2 4.1 7.7
2 2.7 ms 2.2 3.8 7.8
3 2.7 ms 2.2 3.9 7.7
4 2.7 ms 2.2 3.7 7.7
5 2.7 ms 2.3 3.8 7.7
6 2.7 ms 2.2 3.9 7.7

Is that the info you wanted on the injectors?

 

[xtitan1]

Here's what the Scan XL report shows on the fuel injectors:
Injector Value Units Min Avg Max
1 2.7 ms 2.2 4.1 7.7
2 2.7 ms 2.2 3.8 7.8
3 2.7 ms 2.2 3.9 7.7
4 2.7 ms 2.2 3.7 7.7
5 2.7 ms 2.3 3.8 7.7
6 2.7 ms 2.2 3.9 7.7

Is that the info you wanted on the injectors?

Random thread bump but did you get this fixed brother? Curious what was going on...

 

[jimmackey11]

Sorry it's been a while since I've been on here - that day job keeps getting in the way! The problem has just about stopped completely. I got some supposedly heavy duty fuel system cleaner and ran that twice and it seems to have really helped tremendously. Once in a while it will give a little "burp" when in park and closing two windows at one time but it's really random now. I had my local guy check the injector pulse and he said it was right in line where they should be. So, my best guess now is the injectors were clogged just enough to give an occasional stall. Thanks for the follow up!

 

[xtitan1]

Good news man! Kind of makes me want to get some techron or seafoam or something to do as regular maintenance for mine.