Aspen

I think what he is saying is that the half-shafts are not moving when the car is stopped so this vibration issue is unrelated to half-shafts. This is a perplexing problem. I think you need to experience it to get a better understanding. My car is totally smooth at idle in neutral, park or underway, but vibrates when in gear at a stop. It's enough to make cd's in the door pockets and seat belts buzz. It's worse when the car is cold in the morning. Turn on the AC actually makes it better, sometimes. It could be engine mounts, but I doubt it. I have changed everything else but the torque converter and TCU. It doesn't appear to be 02 sensors as the OP changed those. One assumes that the idle would be poor at all times if the cause was due to dirt or faulty plugs and wires. I think I will swap the engine mounts in the summer just to eliminate the possibility.

The OEM plug wires are not the greatest. Age will kill them as much or more than mileage, I would bet on them. ***Beware the HG failure.***

Have the taillights ever been replaced? They need to be sealed with losts of gunk to prevent water from coming in. The window/seal may need adjustment. There are guides on the doors to press it harder, or the glass may need to be adjusted. You should do some detective work with a hose or bucket of water once you have it all dry. Also I once had the window washer line break. It failed at the door hinge for the hatch. It should be on the driver's side. Pull the rubber grommet off and inspect the hose. I fixed mine with some hose splices from the auto store. If your rear washer doesn't squirt, but you can hear the motor running, then this may be it.

Actually I have inspected all the mounts and retorqued all the bolts. There are no visible problems. Also the motor was out of the car for the HG repair and put back in and the problem persists. It may be related to the mounts, but mine 'look' OK. No sign of wear, no rust, no bulges or cracks. I am unconvinced. I gave this problem a pretty good run to try to resolve it last summer. It got better, but it is still there and I find it is worse on cold days with the engine cold. I have been looking for a reason to go with Group N mounts on my impreza, so maybe I will do a switch some time.

Thanks, but I don't think that is it. 1) the wires are new 2) shake was there before and after a spark plug change, 3) it would idle poorly all the time, not only when the car is in gear. I suspect the IAC is still not right, but don't want to buy a new one. Could be a software problem or a sensor issue. DJ3Stripes, the throttle body is the metal part with the throttle plate inside. You see it at the top centre of the engine with a big black plastic air box with tubes behind it. Disconnect that box and spray in a bunch of throttle body cleaner.

My 99GT does this too for a long time now. I would love to cure it. I swapped the IAC unit out, cleaned the throttle body and flushed the trans fluid. It improved but is still there. It's worse when cold or when the A/C in on. Sometimes when it is nice and warm, it is non-existant. If it's the brake booster then why would it be affected by the temperature? I have also heard that the O2 sensor may be causing it. A new MAF is way too much money to chance it. I think I will give the oil tube gasket a try and maybe the brake vacuum a try too.