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Idle too high

1151 Views 10 Replies 4 Participants Last post by  Krem12
Hello Everyone,
Just reinstalled my motor after doing an oil pan gasket replacement. While doing this process, I replaced my CAI from a beat up BBK to a new SR one and a stock throttle body to a 75MM SR throttle body.
Now when I start my car the idle sticks at exactly 1500rpm. Once I unplug the IAC it goes down to 900rpm “where I like it”.
I have traced all vacuum, wires, etc. I don’t want to blindly start replacing IAC’s and TPS’s as I’ve read many people doing that and it not fixing the issue. Btw I cleaned out the IAC as well with TB cleaner.
What am I missing?
Thanks for your responses
1 - 4 of 11 Posts
Have you adjusted the throttle stop on the TB?
Summarized/Corrected Base Idle Reset Procedure (

Try this. TPS just has to be within a certain range, doesn't have to be .98v or whatever.

Get a multi meter on the tps. With Key on engine off, check the voltage. Start the car, TPS voltage should be exactly the same. If its rises without the throttle being touched, replace. Years ago i had a TPS sensor become heat soaked and would randomly raise the voltage, car basically acted like it had cruise control.

Screw is relevant, it sets the base idle. If that screw is adjusted that it allows the car to idle at 1500rpm, the cars going to idle at 1500rpm. IAC cant remove air, only add.
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I ran a 75mm TB on my car with only bolt ons and an intake. It does reduce your "driveability" a tad. For every degree the throttle butterfly opens, more airflow can flow. You'll get to a point where part throttle can supply the engine with enough air for "full throttle" if that makes sense. Is it a big deal, meh not really imo.

The TPS is just something to check, gave me headaches for months trying to track that down.

My bet is still on the base idle screw or unmetered air entering the system (vac leak somewhere upstream of the MAF like @cobrrajet67 said)
Where exactly is this base idle screw? Is it the flat head screw by the IAC? I replaced the IAC by the way with zero success. If this does not fix the issues, I am just going to put my old stuff back on. By the way, it idles at 1500 but once I took it for a drive, it got stuck on 2500. Once I unplugged the IAC the idle was perfect.

SR Performance Mustang 75mm Throttle Body 41114 (94-95 5.0L Mustang) - Free Shipping (
Base idle screw is the screw that the throttle butterfly rests on. Its underneath the throttle body.
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