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Old 11-27-2018, 07:20 AM   #1
ss454rportez
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Idle Problems

Idle is erratic at times especialy when coming to a stop. Takes 3 or4 seconds to idle down. When starting hot it idles in the 1500 rpm range for about 8/10 seconds. Any one know about this ?
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Old 11-27-2018, 04:18 PM   #2
autowiz
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Quote:
Originally Posted by ss454rportez View Post
Idle is erratic at times especialy when coming to a stop. Takes 3 or4 seconds to idle down. When starting hot it idles in the 1500 rpm range for about 8/10 seconds. Any one know about this ?
I have a few thoughts on this subject. First would be a vacuum leak. Places to look are the hoses that lead away from the motor and go to the cruise control actuator, the canister purge solenoid, The vacuum booster. On the c4 the booster is made of plastic. they do separate and leak. vacuum booster vacuum leaks get a lot worse when loaded so step on the brake pedal while the engine is running. Do you hear engine vacuum hissing?

Also Your car is known for Mass Airflow Sensor failures. First on this subject the sensors themselves do fail. They are mounted in the airstream feeding the motor. Between the air filter and engine throttle body. This sensor is powered by 2 relays on the firewall. A MAF power relay that does just like it says. Supplies power to the MAF when the engine is running. And the MAF burnoff relay. This relay powers the sensing wire for a few seconds after the car is shut off to heat up the sensing wire and burn off any contaminants. Failure of these relays and their connectors are common.
MAF power and burnoff relays are mounted together on the firewall on the engine bay side next to the vacuum booster.
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Old 11-28-2018, 11:00 AM   #3
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Scan for Codes.
Check the basics.

1986 model year had many ECM Eprom issues revisions.
All should have been updated under warranty when New.

Have to pull down the ECM from the passenger dash and pull the Eprom cover and check the broadcast Prom chip 4 letter digit code to verify.
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