I have a 1987 Chevy C-10 with a Throttle body injected 350. I did a complete
tune up but it still doesn't want to idle. It stalls and seems to idle real
slow. I don't know if there is a way to adjust the idle speed on the TBI
models. Also there is a rapping sound that only happens when fully warm and
at idle speed. At highway speeds and when engine is cold there is no
rapping. Any ideas? The sound seems to come from the right side of the
engine. Could it be the air pump? You can also hear the rapping comming
through the exhaust, again only when fully warm and at idle speed.
Excessive drag on the serpentine system can cause the motor to idle poorly
and stall out (such as a FUBAR smog pump). So, remove the belt, fire her up
(letting her run for no more than a minute) and see if the problem persists.
This could also be an EGR valve stuck wide open and the "rapping" you're
hearing is actually spark knock. The EGR introduces hot exhaust gasses into
the intake mixture to lean it out and reduce combustion temps, thereby
lowering NOx emissions. If this gets stuck open, you'll be running lean
when the engine is warm and the computer has leaned out the mixture; not as
obvious when cold as the computer is running a richer mixture.
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