New here , so thanks for any help. I have a 1992 Econoline Club Wagon 5.8. Starts right up, but then idle drops rapidly and requires pumping throttle to keep it running. Within about 1/4 mile this stops, but is replaced with a very high idle, sound like about 1500 RPM. Van will cruise at about 20 mph without touching the throttle. I've replaced the IAC, TPS, and throttle cable. I've sprayed carb cleaner around vacumn lines and evap canister while running in an effort to find a vacumn leak and idle speed increase. No increases were found. Any ideas?

 

There is something causing a vacuum leak and the system just adds fuel to usually keep it running. There were loads of vacuum controlled emission controls , are they still on there?

 

Yes, everything is still in place and stock. Here in California, if it wasn't, I couldn't pass smog and renew the license tags. Usually passes with flying colors! It's at about 150K miles. No check engine light coming on either.

 

Did you try around the throttle body with the carb cleaner?

 

Yes, and cleaned it thoughly as well when I replaced the TPS and IAC.

 

Computers are great in vehicles, but they don't always know when you corrected a problem or replaced a faulty part. So,, you might need to do what is called a forced reset~( remove the negative battery cable from the battery post and hold the end of that cable against the positive battery cable to allow the internal memory to discharge ,"go away".
After about 15-20 minutes reconnect the negative cable to the battery post again and start the engine and let it idle without touching the accelerator pedal for a few minutes so the memory can be relearned. Let us know if that took care of the problem.