vibration at idle

Have a 1997 and a 1996 B4V. The 1996 has more vibration at idle. I have checked the part number and on the front motor mount on both vehicles and it is the same. The 1996 motor mount appears good as it does not move excessively when you let the clutch out and keep the brake on. In the past on VW diesels usually when the mount goes the motor moves excessively when you do that.

1. Is it possible the front motor mount could be gone still? I have considered swapping front engine mounts but before that thought I would consult the experts.

2, is there another mount that could be causing this?

3. Anything else to check for vibration.

If the mount is good, compare the actual idle speeds between the two. The '96 could be just a hair lower which you would feel more. I think you can change the idle with Vag Com as well

Vcds. What is the idle QA aet at and how much is it? Harsh idle can be a few things, usually to do with timing and fuel

From the factory, the '96 has a different EDC system. They have a lower idle speed (860 RPM instead of 903). All the '96 cars were under a recall, that got among other things an updated ECU however a few slipped through the cracks. So first, you need to find out if it has the newer ECU. I forget the suffix on t he part numbers now, but someone will certainly chime in here that knows.

Then, you may find that either the front crank pulley is coming apart and/or the alternator may not have the clutch type pulley. In either case, updated versions are available (some '97 Passats and all '97 Jettas already had the clutch type pulley).

If the engine otherwise sounds and runs well, these would be a couple things to check. I actually bought a '96 Passat once that someone had tied a string around and under the accelerator pedal to keep it from returning to rest, so the idle was held up a little higher. If you find that your car's idle speed is in fact 860 and it still had the old ECU in it, and you do not want to source the updated one, you should be able to up the idle speed in one of the Adaptation fields.

Older ECU is BK (black box) the newer is GQ (silver case).

The lower rpm will certainly not help the situation but it also could be just that the mounts are aging and need to be replaced.

And while you're at it would be good to update the passenger rear mount to hydraulic.

Steve