There has to be a major vacuum leak. If the throttle body opening is blocked, air has to be getting in somewhere. Good suspects are a disconnected PCV hose and the hose going to the power brake booster. Check those first.
Do you have access to a scanner? If you do, look under the sensor menu or similar where it lists the "AIS Steps". That's the step number the computer is putting the automatic idle speed motor to. If it is at "0", either "minimum throttle hasn't been relearned yet, at which point idle speed should be too low, or it is trying to lower idle speed, but without success.
On the off-chance the idle step is real high, (it can go as high as step 256), it is commanding that high idle speed in response to a sensor reading that is wrong. No sensor reading can make idle speed go that high, so I'm still sure there's a vacuum leak. Typical idle step is step 32 for a properly-running engine. With a single-cylinder misfire on a V-8 engine, expect to see it at around step 50.
I've also seen cruise control cables fall off the quarter-round guide at the throttle body, and hold it open.
While diagnosing a cruise control problem on my '88 Grand Caravan, I didn't realize the test light I was using created a ground for one of the solenoids in the servo. That caused the servo to pull the throttle wide-open as soon as I started the engine. You'd see that, and blocking the air intake opening would stall the engine.
Jan 3, 2020 at 5:19 AM
