1988 k2500 5.7l 4wd

Let me just start by saying thank you for all the info on this site. I have been lurking for a while, using past threads to solve problems. I have a problem now that I cant figure out.

The motor is a TBI 5.7l with 124,000 miles. It runs strong, burns little to no oil. It idles around 1300 rpm pretty consistently. Ive changed the Iac, and have not noticed any obvious vacuum leaks. Any thing simple that I am missing? When the tranny is in gear (auto) It idles around 500rpm like it should, but it wants to get moving with that much load on the engine.

Also, Ive had a problem with the ESC. It was setting a code 43, and the truck would just run crappy, like it had the flu. Shut it off then restart, runs fine. Get hard into the throttle, Check eng light comes on and it runs poopy again. I use only 91 octane fuel, and I have replaced the ESC. Still have the problem. Would the fast idle be a symptom of this underlying problem? Again, Thank you in advance for any and all insight that you may have. Jason.

 

im having same problem but Check engine soon light won't go out. any help out there?