I have a 93 F-150 5.8 the idle won't drop down, I replaced the IAC it still idles high.

SOURCE: high idle 1997 Madza 626 4 cylinder auto transamission

The PCM controls idle speed to ensure good driveability. The PCM will only attempt to maintain the desired idle speed when it “knows” the throttle is closed. A throttle switch or the TPS input is used to determine when the throttle is in the idle position. Motors and solenoids are used by most PCM’s to control idle speed. Many PCM’s are programmed to attempt to control the idle speed by adjusting spark timing and then by controlling the idle speed actuator. Some computers of the early 80's did not control idle speed.

SOURCE: idle at 1500 to 2000 rpm

Most likely the throttle body gasket (between the throttle body and the intake manifold) is leaking.

SOURCE: Saturn SL 2002 High Idle

Intake manifold gasket. Leaking where intake meets head.

SOURCE: idle out of control.

check all your vacuum hoses and the throttle body itself for a vacuum leaks if the hoses replace as nessasary if to check for throttle body get can of carb cleaner and spray around base of throttle body and sides not in it if idle raises you have a vacuum leak goto a good parts store and ask for a rebuild kit don't goto auto zone or advance they don't carry them

Jta91

• 99 Answers
• Posted on Mar 31, 2010

SOURCE: Saturn 1999 sl Engine has a high idle speed.

The Idle Air Control valve is located on the throttle body. If you follow the intake tube from your air filter all the way back to the intake manifold, where the intake tube connects to is the throttle body. Remove the intake tubing and you can see the throttle body.

There are two sensors on the throttle body and a vacuum line. You'll see two harnesses going to the throttle body, one is the IAC.

However, a quick diagnostic check can be done without touching the throttle body to confirm your problem. If the car has a normal idle when initially started but then rises to a higher idle and stays there BUT then if you were to shut the car off and restart it and it comes back to normal that is the Throttle Position Sensor (TPS). This is also located on the throttle body (the other sensor to the IAC). If it is the IAC it will be high and maybe fluctuate a bit.

Testimonial: "I was the one who listed this problem. Thanks a TON for the info. Now, I'll try to fix it. The ultimate check is if if idles normally."