350 slc idle rollercoaster

[Ron P.]

I have a 1975 European 350 SLC with a four speed manual trans, eight cyl., and fuel injection. When I start up cold the engine races up to about 2500 rpm and then drops down to just about a stall and then right back up, etc. etc... If I can keep it from stalling out and get it up to about 3000 with the pedal, it will run steady until I let up on the gas, whereupon it will resume rollercoasting. If I disconnect the 2-prong lead to the intake horn on the air cleaner housing and jump it out, the problem will immediately diminish, only to resume as soon as I reconnect the plug. When the engine warms up, the effect disappears. The guy who sold the car to me was told that this was intentional on the part of M/B, but it sounds like a crock to me, but who knows?? Regardless, I need to eliminate this because it's almost impossible to drive until it warms up. Any ideas??

The cold idle speed is too high causing the injection to enter "decel-shutoff" until the rpms drop. This can be due to over advanced timing, an intake leak, a faulty auxilliary air valve, or anything else that will let the engine speed go too high at closed throttle. It is part of the design of the system.
Regards,
Randy D.

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