I have a 1990 Cougar XR7 with a 3.8-liter supercharged, fuel-injected and intercooled engine. I am the original owner and have kept it as my toy! After driving it about 30 miles on a series of errands, I got off the toll road and when I got to the light it would not rev down.
Now when I start it, it revs up to about 3,000 rpm and then will drop to about 2,000-2,200 rpm. I have never had any engine problems, and it has less than 60,000 miles on it. What is wrong? How do I fix it and how much will it cost?
This may sound silly, but first check the accelerator pedal itself. Be sure it didn't get hung up on a floor mat, or the attachment hardware has come loose and bound up the accelerator linkage.
Then go under the hood and take a careful look at the throttle body assembly on top of the engine. We want to be sure that the throttle plate is closing all the way when you take your foot off the gas. Something may be obstructing the throttle linkage, or the throttle body itself can be messed up. You can also go as far as disconnecting the throttle cable from the throttle body. If the throttle plate then closes, there may be a problem you missed back at the pedal, or the cable itself is binding up.
Other issues that can result in extremely high idle speeds are large vacuum leaks, an inoperable throttle air bypass valve (controls idle speed), or a computer and/or sensor problem improperly instructing the throttle air bypass valve to raise engine speed. It shouldn't be too tough to track down.