Tercel'98 shaky at idle - please help!

[mrblack1134]

Ok, I need your help.

I have an automatic '98 Tercel and for the last few months I've had this engine shake problem that I'm trying to solve/diagnose. The shake is actually a lot more obvious from inside the car where you can hear some kind of knocking/shaking against the frame of the body (or at least that's what it sounds & feels like).

I can only hear the shake/feel the vibration of the car under the following conditions:
- when in drive or reverse & holding the break; it doesn't do it in neutral, neither when I give it a little gaz (in which cases the RPM is then a little higher)
- when the engine is warm (ie, I need to drive 10-15 minutes and go at around ~ 40mph, then stop at a red light)

I took it to the dealer, got the sparks & ignition plugs replaced but nothing changed -- they initially tought it was a misfire, but I'm convinced it's not the case (I've had worned out spark wires before and know what a misfire feels like). The RPM on drive while holding the break is at round 600rpm (using an ODB2 reader from the dealer) which I was told was normal.

I do not feel any loss of power/responsiveness from the engine.

At this point I have 2 main suspicions:
- rear engine mount (the one attached to the tranny and the body frame)
- intake problem (stuck egr valve and/or leaking intake gasket when hot?)

I was told by the dealer the rear engine mount _rarely_ goes bad on Tercel's. I've jacked the car, looked at it, and the rubber looks fine inside -- really hard to tell if it's bad or not. One thing I *should* try to rule this out is slowly jack the engine from the oil pan while somebody holds the break (and the engine shakes); if it fixes it, then chances are it's the mount, right?

Any other suggestions? (how do I diagnose a stuck open EGR? can I just pinch/disconnect the hose temporarily to see if it fixes it?) or do I have to take it all out and clean it?

Thanks

[90celica]

I would do a compression test

[4speedsleeper]

Motor mounts would cause shaking.

[scys]

My 95 tercel does the same thing. I would bet it was the motor mount. To check both possible things you have suggested I would get a second person to help you.
For the motor mount I would have the person helping you hold the brake giving it a shot of gas at the same time. While you were watching the motor mount. Do this in drive and reverse and see how much it moves.
For the Egr you could have the person rev the car and with you hand on the egr diafram, it should move. You could do this by yourself if you just reved it from under the hood.