After fixing a surging idle problem by replacing MAF, the car now idles evenly at 550 RPM in gear and 700 in neutral.
The car idles evenly but not smoothly, meaning it maintains a steady 550 but there's unpleasant engine vibration while in drive at stand still. Up until a few months back, the car idled at red lights so smooth you could hardly tell the engine was even on. In Nuetral the idle is smooth. In reverse at stand still the idle is smooth. Its only in drive that there is medium to heavy vibration.
At first I thought maybe there is still a vacuum leak somewhere. But now I am beginning to think that months of driving with a bad MAF may have deteriorated the engine mounts or perhaps the caked up the oxyen sensor with carbon.
I jut cleared the error codes when replacing the MAF and since have driven about 30 miles in 5 trips. The CE light has not come back on.
I would really like to get back to that smooth as glass idle.
One more possibly related symptom - the air pump stays on nearly 5 minutes after start up and sometimes comes on for 30 seconds even after driving 10 miles. I've had CE ligth come on in the past for code 26 (faulty shift delay) My Indie advised to ignore it stating it could be a $300 repair for a problem that was not doing any harm.
1995 E320 with 217K miles

tan man, it's time to replace the engine mounts if they are the original ones. Stay away from Uro engine mounts. Either buy them from a MB dealer or buy ones made in Germany. Best to replace the transmission mount at the same time.

Replaced the engine mounts on our 1995 E320 recently. It's a relatively simple DIY job if you have a floor jack and ramps/jack stands, or access to a lift. A quick summary follows:
1. Raise car high enough that you can work under it comfortably.
2. Remove both engine mount to cross member 17mm bolts.
3. Jack under the oil pan to raise the engine mounts clear of the cross member. (Place a short length of 2 x 6 under the rear of the oil pan to prevent damaging it.)
4. Remove the four 13mm engine mount bracket bolts on each side and remove the engine mount/bracket assembly.
5. Replace the engine mount on each assembly (a 17mm bolt secures the engine mount to the bracket) and reinstall the engine mount/bracket assembly on each side.
6. Lower the engine so the engine mounts contact the cross member and reinstall the 17mm bolts. A drift pin may be needed to align the bolt hole with the cross member hole.
7. Lower the car to the floor.

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Fred Hoelzle