Hmm...

I got my -89 760T automatic station wagon back from an oil change today, and a new interesting noise presented itself.

No warning lights are on.

A bit rough at warm idling, but no stalling or other bad stuff. This is new.

Lately (also before the oil change) cold starting has been rough for the few first seconds where it didn't fire on all cylinders. After five seconds everything comes on line, though.

The noise:

When I take off with about half 1/4-1/2 throttle, I hear a rattling noise that I initially thought was a loose heat shield or the exhaust system vibrating against something. The noise disappears at full throttle or if I step off the gas completely.

After awhile I started to get paranoid, and now I am posting this message.

My guess right now is that the shop disconnected the battery and thereby resetted the computer, and now the computer is trying to get its bearings. Hence the rough idling.

But if the rattling is indeed knocking, the knock sensor should immediately detect any knocking and retard the ignition.

Also, could an unfiring cylinder cause this?

Suggestions?

Thanks in advance for any help.


Tnx!