I have a 94 cavalier. The car has a shaking noise right from reverse to drive gear. At neutral, there no shaking nor shimmering. At the traffic light it shakes terribly inside whiles I'm at a stop on red. I've tried to figure out the noise but to no avail. I've opened the hood with engine running just to see the source of the shaking but the engine is solidily in place. Can somebody help ...,

 

Did you check all your engine and transmission mounts?

 

Yes....they didn't look pretty bad but I'll go ahead and change them together with the transmission mounts as well. Hopefully it fix the problem.

 

you can't always look at mounts the compression can hide the crack (ie, put sire under, lower car onto, see if stretched rubber mounts have no tars - without tearing them of course!)

but before that: doing things in right order.

insure you battery is ok (yes, 5 cells instead of 6 can cause strange things, test it good, no test is "trusted" until this one passes!)

get a engine code (odbII testers are $35 online now?). if either trans or engine throw code resolve them first. but still make sure you engine and trans and trans-engine connectors are ok and have no (lack of) ground issue.

triple check your fluid is clean, the right kind, and at the right level warm (not too high)

insure your mechanical linkage is ok (shifter)

deep in the trans there's a fluid circuit with solenoids. may be sticking. a trans flush (by a shop with a flush machine) might free it

if wrong fluid or belt damage - then belt might "bump & slide" before catching on drum - unlikely but that's the end product

 

(if your shifter linkage is wrong it can cause odd shifting behavior esp P,N,D,R)