01extreme_chevy: just replaced the pre-cat/cat cross-over about 5k miles ago so doubt that this is the problem; besides if it were the cat it would probably do this when in neutral as well.

Sure would like to hear from eistered if replacing the torque converter and lockup switch fixed the problem.

I read somewhere that there is a lockup solenoid in the 4L60E trans....just need to read more about this.

 

Lanny, did you use AC plug wires. Mine had some aftermarket ones on and would idle rough. With side mud guards off looking in from the fender wheels it looked like fire works on 2 plugs from jumping fire. I checked it in the dark.

 

Sounds like motor mounts are toast, I'd check these and your trans mount.

 

I had that problem also and the Blazer only has 100k on it. I think they had faulty mounts. I hope for Lanny's sake that's not the problem. All but impossible to do without a lift and still not a pleasant job with one.

 

Spark plug wires: nope did not use Delco, used the ones that were recommended here...just cannot remember the brand at this moment. Besides idle is nice and smooth when in neutral; also drives very nice, so I doubt that there is any kind of misfire happening. But will check this morning since it is still dark outside.

What is a good way to check the trans and motor mounts?
As far a changing the mounts; does the engine need to be lifted? I sold my engine hoist several years ago.....I knew I was going to regret that!

Did about an 80 mile roundtrip yesterday, mostly highway and up to 80+ mph. When I exited the highway and came to a stop, the rough idle began immediately and was very noticeable, putting into neutral and all smooth. I think I am getting closer and closer to a trans rebuild, but will check the mounts today.

Thanks for the suggestions.

 

I would replace the mounts before rebuilding the trans. You don't need a hoist, I've replaced these with a bottle jack under the oil pan. Chances are your motor mounts are already cracked and separated- just unbolt the two nuts on the trans mount and you should be able to jack it up about an inch and fish all the old mounts out.

 

Lanny, my mounts where bad also but to visually just look up under the truck they are rather hard to see and I don't know if that would tell you much. But they are known culprits. I found mine where bad when replacing the freeze plugs. You definitely want to go ahead and replace those (freeze plugs) also if you get the mounts out of the way. Mine at idle would beat the exhaust pipe on the frame or something and shake.
I for one would in no way shape or form attempt putting those motor mounts in without a lift. It was a job doing it on the lift much less on the ground standing on your head. If your young ang have a strong neck from looking up maybe. Where there's a will there is a way. Do a search on here about changing motor mounts. You will find 9 out of 10 say do it on a lift because it is not an easy job. That's my opinion and you will find many others that will tell you the same. Once you get under there and look real well at what your up against you might feel the same way. Good luck and keep us informed.

 

I removed the front wheels and fished the motor mounts out through the wheel wells. If you've attempted this type of work before it shouldn't be that difficult. I used a combination of u-joint sockets and wrenches that were bent/cut down for clearance. I used the jagsthat run 2.8 motor mounts, the stock mounts are a bad design..

S10 4.3 V6, High Performance Replacement Mounts for 2WD W-10 Trucks & Blazers, Stealth Conversions

 

Lanny, did you ever fix this problem? Mine has started doing this a couple weeks ago. Rough idle only when in drive and reverse. In park it's fine. At stops, rpms and oil pressure drop and wants to die almost. It also hesitates on take off from stopping. I might make a new thread but found yours and it sounded similar thanks man.

 

Nope never did. I have yet to even try to replace the motor and trans mounts; perhaps this Fall when garage temps are a bit more comfortable.

From what has been posted here about needing a lift and all...not looking foreward to this job.