TBI high idle
 

Have a 92 chevy truck 454 TBI, idles so high I can drive it 15 to 18 mph without touching the gas. I have checked lines for vacuum leaks, replaced TBI gasket, IAC valve, PCV valve, EGR valve, Coolant Temp sensor. Any ideas. would help.

Re: TBI high idle
 

No codes? If you already changed the IAC, then the computer must be sending it false voltage signals. Possibly not reading RPM correctly? Did you clean out the hole where the IAC plunger rides?
If all else fails, you could bug Ed Wright about it.Don't tell him I sent you.

Re: TBI high idle
 

No codes coming up on dash, cleaned IAC out good to.

Re: TBI high idle
 

We had a problem when we built the Monte. We were driving it around before we took it apart, and all of a sudden certain functions quit working .Not having any way of getting inside the computer, we just bought a used one for 50 bucks.
That fixed everything.
Just had to follow the procedure to unlock it in it's new home.
Might be worth trying at this point.


Just noticed you didn't mention the TPS switch.

Re: TBI high idle
 

Years ago my low mileage 92 c3500 did the same thing. I replaced every part you did plus the cold start injector, tps sensor and even the ecm. I finally replaces the 10 dollar coolant temperature sensor located by the thermostat housing on the intake and that fixed it. There is another sensor on the drivers side head but I believe it's for the temp gauge. I spent a couple hundred dollars throwing new parts at it. I unhooked the battery to reset everything and finally got the "check engine" light to come on. I used a scan tool but don't remember the code. This might not help but you are not the only person that has had this problem.

Re: TBI high idle
 

Years ago I had the same issues with my 89 454 dually and it was the coolant temp sensor also.

Bruce Cameron

Re: TBI high idle
 

Best advice I can give you is to find someone that owns and knows how to use a scanner, barring vacuum leaks incorrect data from one of several sensors can cause this issue. A few dollars spent diagnosing the problem can save a lot of money and frustration.