Excessive vibration in gear at idle, but not neutral. Why?

[DrAnonymous]

So, my 83 rabbit seems to idle fine. If I put it in gear, I get some vibration that seems a little excessive. If I turn the AC on, it sounds/vibrates like its a helicopter getting ready to take off. :/

If I put it in neutral with the AC on, its nice and smooth. I changed all the motormounts about a month ago, so I don't think that's it. I also turned up the idle a little. Driving its nice and smooth.

The other threads here on vibration didn't mention a difference between being in gear or not, so I thought I'd mention it and start a new thread.

Ideas?

[CarlosA]

I've got a little bit of this too, mine is no doubt because of the long belt stretched up to the alternator with the AC compressor removed. One example is when I first start up and the alternator hasn`t engaged yet, its smooth. Once the revs pass 950 rpm or so the alternator kicks on and the vibrations start. They really aren`t out of control but I think the issue is in the belts/accessories systems for you.

Did this start after all of the work you recently did to the accessories? Is it really in the engine compartment or just your dash vibrating like crazy? My dash vibrates a lot more with the knee pad out (while working on stuff), and with the passenger door open. These cars rely on the knee pad and the closed doors for a lot of the structural rigidity.

Someone else will probably come along with a lot better explanation and solution though.

[82vdub]

Is this an auto trans you're talking about, or manual trans? When you put it in gear, is your foot on the clutch pedal or is the vibration when you're letting the clutch out?

When you redo motor mounts, you will take a sloppy mount and tighten it up, so you can potentially take any vibrations that the sloppy mount let the engine flop around and as the engine is held more secure, the vibration will go into the chassis.

[DrAnonymous]

I have an automatic tranny.

Its just weird to me that putting it in gear and stopped it vibrates so much. The AC being engaged with the tranny in Neutral is nice and smooth.

I don't know what the vibe was like before the work I did, because it wasn't running prior to that. I could have waited on the motormounts and maybe that would have shed some light.

[82vdub]

Is there a solenoid anywhere or other provision that raises the idle RPM when the engine has the AC turned on? If it does, that's probably the reason why it idles smooth when the AC is on. Maybe you can hotwire that solenoid so that it's manually operated (along with auto operation with the AC) or that it's always on??

[joat]

just a suggestion:

try turning the idle DOWN .... as the rev's increase, the auto tranny engages the clutch packs ( starts to lock up ) and transmits the engine pulses to the drive train.