. . . though not due to Iffy Lube places. On the M116 motor there is a vacuum line *under the air cleaner assembly* -- a little rubber hose that can come loose from a nipple on the manifold and cause the rocking and rough idling you describe. I watched my regular mechanic fit it back into place.

Three months later, on Christmas Eve, yet, the same symptoms recurred, but the car was drivable. This time, after taking off the air cleaner, I used a stereo wire cable to snug the hose back into place. Problem solved.

I dunno if your 300TE would have its vacuum line in the same place, and they wouldn't have had to remove the air cleaner to change your oil (at least, I hope not). Look for a vacuum line near the filter, would be my guess.

__________________
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-- Paul W. (The Benzadmiral)
('03 Buick Park Avenue, charcoal/cream)
Formerly:
'97 C230, smoke silver/parchment; '86 420SEL, anthracite/light grey; '84 280CE (W123), dark blue/palomino