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87 420SEL, starts and only runs a few seconds

18717 Views 41 Replies 9 Participants Last post by  waybomb
87 420SEL, starts and only runs a few seconds - Still need help

Have a 1987 420SEL. 140,000 odometer.

Start the car, rpms come up slow, idles fine, then races and shuts off. If restarted immediately, the process becomes shorter. If a wait of a few minutes, the process may take 45 seconds.

3/4 tank fuel, replaced the fuel filter today, still has same problem. The pumps are running, air filter ok, no wires seem to be off anywhere.

Any ideas on what to check?

Thanks in advance.
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I know you have local sources, but I have a few ICV and ICR (speed control) units in my garage, if you need 'em.

PM sent.

It must be the Idle Speed Control black box. The thing leaves the ICV wide open. When it is racing, I can unplug the connector with no change, even though when cold, if I unplug it, the engine races, and settles down as soon as the valve is plugged back in.

I did open the ISC. The piggy-back board was all sticky. Maybe overheating, though it never felt hot. I wiggled it around with the cover off which resulted in no difference.
OK, just going back over old posts:

A different ICV brought the idle down to about 800-1000, replaced the ezl with a good used one which cured the dying after racing symptom, and finally replaced all the air hoses to get the idle down to 600.
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