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Re: Misfiring just above idle (archive)
[ Follow Ups ] [ 7-series (E23) Message Board ] [ Msg. Board FAQ ]
Posted by Bigbob 85 745iA on January 26, 2002 at 22:08:04:

In Reply to: Misfiring just above idle posted by Charles V. Stancampiano['84 733i] on January 26, 2002 at 21:47:49:


Lately I have noticed the engine in my '84 733i (US version with 157k miles) is sounding like a motorboat just above idle (1300rpm). Above or below is fine. Sounds like one cylinder is not running, but just at that speed. It is much worse when the engine is cold than when it is warmed up. Car starts well and idles OK with a little hunting.

Recent work: exhaust system, throttle cable, brakes, clutch master and slave cylinders.

Possible suspects: O2 sensor is old. Plug wires...

Other strangeness: Removing the oil filler cap or dipstick does not cause the idle speed to change although I distinctly remember both these actions causing the idle to go crazy when the car was new.

I am tempted to replace ignition stuff first. Any ideas?
Thanks.
Charlie

You could have a bad or leaking cold start valve. If it's leaking, it will constantly dump fuel. I would also disconnect the 02 sensor while it is running and see if it stops hunting. If you remove the oil cap or dipstick, the engine should want to stall. You may a loose or cracked vacuum line. It also could be a leaking valve, but I would check the easy items first.

Bigbob




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