I just replaced my idle control unit, which fixed my high idle. It was 1400, but is now a nice steady 650. However, it still has the same "stumble" it has always had when first started. The car starts instantly (even at -5)and for about 30 to 45 seconds, idles at just above 500 rpms, then the rpms will start dropping and for 30 seconds to a couple of minutes it will drop so low it almost stalls (sometimes it does). Then the rpms start to increase until it is idling normally (650 rpms). (Before I replaced the ICU it would increase until it idled at 1400)

Can anyone give me clue as to what this could be. Cold start valve, maybe?

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2000 Mercedes S500
1990 Mercedes 560SEL
1970 Triumph Spitfire

CIS injection uses a basic principle of a system fuel pressure VS a control pressure.

99% of running problems are related to fuel pressure differential. You need to have the fuel pressures tested!

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MERCEDES Benz Master Guild Technician (6 TIMES)
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Retired Moderator

check the voltage protect relay there is a fuse on top which sometime will not make good contact.. this relay supplies voltage to idle control module.. if that is ok have your fuel pressures checked
Bob

could also be a gasket. go around spraying PB blaster - the intake gasket and the gasket for the A/F ratio was my problem.


Could also be a fuel warmup regulator; again - check your pressures.

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-1983 VW Rabbit LS Diesel (5speed, VNT/Giles build)

Remove the idle control valve and flush it with a few blasts of carb cleaner. It gets dirty and sticky in there.

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1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma