Replaced motor mounts and now I have a rough idle

[BanditGTP]

Thanks to some help from ROADIE, I've made it here. I came over from the "other" site since there isn't much action over there these days.

So like the title says, I replaced my motor mounts and ever since then, I've had a rough idle. Here's a breakdown of the sequence of events that led up to this point.

Replaced motor mounts (battery was disconnected while performing the repair)
After replacing mounts, the rough idle started. It doesn't stall out or throw any codes. RPMs will jump up and down approx 200-300 rpm.
Cleaned throttle body and changed spark plugs. Removed throttle body to clean it and battery was disconnected for approx. 2 hours while doing repairs.
Tried disconnecting battery one more time and let truck sit for 1 hour.

The truck has been driven for at least 2 months and 2000 miles since changing the motor mounts.

So I know about the problem with the PCM relearning and cleaning the throttle body to fix the problem. I had that problem once before (about 2yrs ago) when my battery died. At that time, the idle was rougher then now and the truck would occasionally stall out when coming to a stop.

I'm not sure what else it could be that would be logical since it only started right after the motor mount replacement. I know I've read that it could be a bad/defective spark plug but it's not giving me any codes and the trouble started before I changed the plugs.

Any ideas or suggestions would be appreciated.

 

[AtlWrk]

Welcome

What brand of motor mounts did you use?
There have been reports of aftermarket mounts being incompatible and causing rough idle.

EDIT: just re-read your post and saw the part about your RPMs fluctuating. That would not likely be the mounts...

 

[BRomanJr]

Thanks to some help from ROADIE, I've made it here. I came over from the "other" site since there isn't much action over there these days.

So like the title says, I replaced my motor mounts and ever since then, I've had a rough idle. Here's a breakdown of the sequence of events that led up to this point.

Replaced motor mounts (battery was disconnected while performing the repair)
After replacing mounts, the rough idle started. It doesn't stall out or throw any codes. RPMs will jump up and down approx 200-300 rpm.
Cleaned throttle body and changed spark plugs. Removed throttle body to clean it and battery was disconnected for approx. 2 hours while doing repairs.
Tried disconnecting battery one more time and let truck sit for 1 hour.

The truck has been driven for at least 2 months and 2000 miles since changing the motor mounts.

So I know about the problem with the PCM relearning and cleaning the throttle body to fix the problem. I had that problem once before (about 2yrs ago) when my battery died. At that time, the idle was rougher then now and the truck would occasionally stall out when coming to a stop.

I'm not sure what else it could be that would be logical since it only started right after the motor mount replacement. I know I've read that it could be a bad/defective spark plug but it's not giving me any codes and the trouble started before I changed the plugs.

Any ideas or suggestions would be appreciated.

Please fill out your profile or tell us the info on your vehicle including the mileage, there are slight changes through the model years.
Start by looking in the vicinity of the mounts for damaged wires, hoses or unplugged components. I also agree to elaborate on what brand Motor Mounts were used as AtlWrk asked above.

On the passenger side, towards the front of the engine the CPAS Solenoid is highly suspect, check out the wiring there.

On the drivers side, low on the engine, check the purge valve piping and wiring.

 

[CaptainKD]

Welcome aboard!

 

[BanditGTP]

Thanks for the responses. I forgot to mention the specifics on my truck.

It's a 2003 Envoy XL 4X4 with the 4.2 motor.
Mileage - 155,000 miles

The rough idle definitely started right after the motor mount replacement. I was about to go aftermarket for the mounts but then read about the problems with aftermarket so I went with OEM from GMPARTSDIRECT. It was like night and day between the old mount and the new mounts. Now I just have this rough idle.