Thread: High Idle Problems (After Intake Gasket Replacement)

I am finishing up an intake manifold gasket (upper & lower) change 2003 Grand Prix w/ a 3.8 w/o a super charger. While I was in there I cleaned the throttle body and Mass Air Flow Sensor. On first start up it was idling at 2500 RPM then spiked up to 4000 RPM. If I disconnect the Idle Air Control it still idles at 2500 RPM but does not spike up. Disconnecting the Throttle Position Sensor or Mas Air Flow Sensor has not effect on the idle. Disconnecting the air flow sensor in the intake tube causes to idle to raise slightly. The check engine light comes on immediately. I don't have a code scanner on hand to check the code. I also checked to make sure the throttle cable was letting the throttle body close all the way and it is, has just a slight amount of slack in both cables. Where should I look next? I am stumped.

Start the car a spray carb or brake cleaner around all the vacuum lines, TB, EGR tube (the metal accordian one that likes to break and hide leaks) and the UIM. Might just have a big leak. Also check the big vacuum line at the firewall side of the UIM where the line from the brake booster connects. Also, check the MAP sensor if you removed it.

Found the problem yesterday. The throttle body was not properly seated properly allowing it to suck a bunch of extra air. Backed off the bolts and re torqued them and idle is fine. So you were right I did have a big leak!!! Thanks for the help.

After some checking with a code scanner the TPS bit the dust during the repair. After new TPS it runs great.

You're welcome. Thanks for posting the resolution. Sucks on the TPS but at least all is well now.