Hello all I am new to the forum and this is my first post. My '86 2.8l automatic has developed a near redline idle when put in park or neutral after driving but not upon startup. Has anyone else experienced this or have any input that could help me? Thanks.

 

Sounds like your throttle is stuck, see if the return spring on the throttle body broke.

 

Dave's idea is spot on if the engine is actually revving that fast . Is It ?

Are you sure the engine itself is actually turning , what 5500 RPMs ? If it is , it should sound as if you took any other car and floored the gas in park , namely the engine would be screaming like a banshee (or an air raid siren) and sounding as if it will leap out of the hood or grenade at any second . If the RPMs really were that high , you'd either break drivetrain components (Ujoints , gears , etc) if it actually went into drive from N or P with that kind of RPM or you'd launch with 20 feet of burned rubber behind you .

I ask all this cause the Tachometers in these cars are notorious for failing in such a way that they read high , It's SO common a problem that a regular member here (sofakingdom) is planning to market a better built circuit board with all the right parts in all the right places so it won't fail like the factory ones do . Now , if it is really revving like crazy and the throttle return spring is ok , next up would be to check for a sticking IAC that hangs open when at operating temp but closes properly when it needs to when cold .