hey guys ive got another question. Ive had a high idle problem for about a year now ive replaced the TPS and cant remember if i changed out the IAC but im thinking i havent. at any rate I did a voltage check on the IAC and per haynes it should be about 10.5 volts and im getting a little over 12. my idle is about 1200rpm tonight i decided to disconnect the IAC and the idle went to exactly where it is supposed to be 650 - 700 so i drove it to work that way and about half way to work it kicked back up to 900 - 1000 no ac or heater running. anyone have any ideas what else i should look at as far as what controls fuel air mixture. I'm guessing that the IAC might be partially at fault. also i pulled the IAC off and checked to see if it was free and it is, with minor residue on the valve. any ideas would be appreciated

thanks

 

Obviously, you're getting some extra air in the engine from somewhere. It should barely idle for ~10-30 sec before dying with the IAC unplugged. Try using a 3' piece of garden hose as a stethoscope to listen all around the idling engine for an obvious HISSSSSSS. Also check around the top of the brake pedal, around the "coffee can" & the plastic ball (both vacuum reservoirs) on the R wheelwell, & around the cruise servo (if equipped).

 

I had a 1989 300 with the same problem. It first happened when I cleaned the throttle body. Check the throttle body gasket to the intake. I had to change mine 3 times over 12 years. It's not a hard job I think it its only 2 bolts. Edal