Thread: Slow/rough idle
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Old 08-13-2002, 12:26 PM
Posts: n/a
Slow / rough idle 1987 300E

I recently purchased a one owner 1987 300E with 67,000 miles. My basic problem is a SLOW/ROUGH IDLE. The engine speed is approx 650 RPM. Above 1000 RPM it runs fine. Additional note is that it did passes the California smog test. (for whatever thatís worth) Unfortunately there is no idle adjustment screw or I wouldnít be addressing this forum.

Now for a list of what I have done so far with no change in the idle performance.

A plug check shows that the rear three cylinders appear lean and the front three cylinder are definitely rich. Spark plugs, cap, rotor and wires have been replaced. Both ignition timing and cam timing have been checked and are on spec. Interestingly the cylinder pressure is good at 150 psi, but the vacuum reading is low. I have replaced the fuel filter, fuel distributor, injectors and seals. The fuel pressure is 85-90 psi.

That's about it. Any suggestions would be appreciated. (just point me to the idle screw and Iíll be out of here!)


Last edited by rtarozzi; 08-13-2002 at 12:37 PM.
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