High Idle And Poor Mpg

[Slobin3d]

I have a 95 5.0 5 speed, what I know that has been done to the car: CAI, Non Stock headers, "offroad" 2.5" exhaust, X pipe, no cats and high flow mufflers. SCT selective tuner.

I'm idling at 1100 cold and 950 warm. I tried the Setting base idle with no improvements.
I turned off the SCT tuner with no change either. Unplugged the IAC and the car dies after a second, adjusting the idle air bleed screw only increases idle and is currently set at about 1/2 turn from closed.

The Idle doesn't hunt, in fact works as you would think is should, just higher then normal.

As for MPG I'm averaging 10-12 with or without the tuner


Help

 

[toyman]

Do you have actual numbers for the operating engine temperature? Have you checked for trouble codes? Without having verified knowns solutions at best are just guesses.

 

[Slobin3d]

i have no CEL, and it runs right at 200 according to the dash gauge, how accurate that is??

 

[toyman]

The absence of a CEL doesn't mean there are no codes. Since the stock gauge only reads "NORMAL" how do you know it's 200*F? The relative position is meaningless. In particular the idle is a commanded parameter and as such the ECU will try to maintain that parameter. So many things can be causing the high idle. That's why engineers designed the ECU to log events.

 

[Chythar]

The engine should be able to idle just fine with the IAC unplugged. The IAC is mainly there when you're at idle and have a heavy load on the engine, like the AC on full blast. The high idle and bad mpg make me think you have a vacuum leak somewhere. How are your vacuum hoses? Any dry rot? Are the plastic colored vacuum hoses still intact?

 

[Slobin3d]

It has one of those cheap aftermarket guages, the stock one works too, but yes reads a little left of center normal. I haven't checked for vacuum leak yet, will do and report back