John,
Just got my car back from its 120k service. Was kicking around theories about my intermittant rough idle and after talking about the usual suspects (distributor caps, rotors, etc) an idea struck him. He has replaced the rubber "doughnuts" between the engine and intake manifold on other engines and found this to be helpful. He showed me some which he had replaced and they had visibly deteriorated, causing an air leak.

He said these can be tested by hooking up a handheld tester, monitoring readings from the O2 sensor, and spraying the area around the rubber doughnuts with something (carb cleaner?). This won't produce a noticable change in RPMs but will be seen on the tester.

Just another thought.

__________________
Steve
'93 400E