Vannin' Home Forums Chevy Troubleshooting 1993 G20 4.3 V6 vibration when idling in gear

My van has a significant vibration when idling in drive or reverse. There's a little while idling in park or in neutral, but much worse when in gear. And only when idling - give her some gas and it smooths out.

Just spent the weekend replacing both motor mounts and the transmission mount (all aftermarket) but unfortunately the vibration is still there...

Any thoughts on what I should try next? Or just accept that I'm getting a free chair massage at red lights?...

I should also say that the vibration itself is very consistent. Not bouncing around like I would assume a rough idle would.

Harmonic balancer ...

Thank you very much! Next on the list!

Should I change the pulley while I'm at it, or does that typically outlast the harmonic balancer?

There are three versions of the 4.3, the later had the balance shaft. If you have plastic valve covers there is a good chance you have the stronger odd fire engine. Look up what you have. Check your balancer like frscke1 said, remember if the balancer is external balance the outer ring can slip and be out of place and be out of balance. If you have the balance shaft engine, the shaft may have jumped a tooth. GM used nylon gears back then for noise reduction. Back in the 80's many cars went to the boneyard for broken gears at 75k on the clock. The other thing to look for is the balance weight on the flexplate, it is spot welded and can break off. If you have the odd fire engine you may need a timing chain set. Of all the stupid things make sure you're running on all cylinders. Plugs, wires, cap, does 93 have the fuel injector spider? Are you getting fuel to every cylinder?

Some low cost thoughts:
Check for a stored code.

Check the PCV valve and tubing for clogging, leaks or poor operation.

Check the throttle linkage for smooth operation and closure without binding. Also you'll need to check that the throttle and TPS are adjusted properly. The TPS should read less than 1.25 volts with the throttle closed. If the throttle stop has been messed with in the past it could be off.

A quick check for any small vacuum leaks using some starting fluid would be easy and cheap.

Other thoughts:
Does the engine idle change or smooth out with the AC turned on? The module should raise the idle slightly when the compressor is engaged. If not then you may have a communication problem with the AC control and the module.

You might want to remove the IAC and check it for proper operation and cleanliness. (The internet can tell you how to properly set it for a reinstall).

A leaking injector can cause a rich idle and can be hard to spot if it's only a slight leak.

Also know that the 4.3 V6 engine is not a smooth idling engine anyway. An internet search will show you quite a bit of info and a search of some of the S10 forums will reveal many threads on the subject.

My2%

Thanks jcd74!!! The Haynes manual implies that only the 1995 4.3 V6 has the balance shaft - is this the one with the odd fire? I assume mine isn't this version since it is a 1993. Still worth it to check the flexplate I guess, and thanks for the advice.

Great thoughts CatFish - thank you. I just replaced the PCV but didn't check the hose, and I'll certainly look into the other things you mentioned. I just tried to see of anything is different with or without the AC on, and I'd say that it doesn't really change anything regarding vibration. I can feel the compressor kick on, but I guess the extra RPMs aren't enough to get it out of the "vibration zone".

Haynes manuels are basic what you need is a Factory Service Manuel

Amazon has them in the auto section

Both early Astros I have shake, I don't pay much attention to it anymore..lol