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1996 buick century-high idle ??


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good afternoon folks

on a cold am when starting the 1996 century(fuel injection)-it high idles like crazy.

I have to drive about 4 miles for the idling to come down

when the car is just in drive it is going about 35 mph, not even stepping on the gas

what do you thing the problem is ??

many thanks

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With an appropriate scan tool, you can check the TPS percentage, BUT it could also be a sticking stepper motor in the throttle body. It's the stepper motor which regulates air bypassing the throttle plate when it's closed, at idle. It might well be that a good cleaning of the throttle body could take care of the issue, but some GM throttle bodies are either not cleanable, with a reasonable degree of success, so replacement is the only real option, in that case (regarding the internal passages which the stepper motor control). On some throttle body assemblies, the PCV "gasses" are added to the intake manifold tract just behind the throttle plate, which can also allow them to migrate into the throttle body passages under certain conditions . . . why the throttle body might need to be removed for inspection and cleaning of the internal idle passages.

What you might investigate would be to get the throttle body internal passages cleaned, the throttle body "plate" area cleaned, then let it sit overnight at the repair shop and have them check for proper operation AND also the TPS signals to the ECM (that the indicated %s match actual throttle opening %s).

With the cold engine, you can also check (as it warms up) the signals from the ECM's engine temp sensor, which can possibly have a modulation of the idle speed as the engine warms up. If the temp sensor is "lazy", it might delay the ECM knowing the engine can tolerate slower idle speeds after the cold start.

Sometimes, too, a "deposited" EGR circuit can prevent the EGR valve from fully seating at idle (or other times it should be closed). But I would suspect that would set a code.

Worst case scenario, it might be an intake manifold leak that closes as the engine warms up. Try the easiest and least expensive things FIRST, though.

Just some thoughts,

NTX5467

Edited by NTX5467 (see edit history)
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in terms of the throttle position sensor

would the car have to be high idlin g in order to get the code ??

when the idle returns to normal-then if using the scannner-would the code still show up ??

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