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Idle too high

1149 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
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Have you adjusted the throttle stop on the TB?
The little screw by the spring? Yeah several times. I have read that that screw is pretty irrelevant considering the computer does all the adjustments. Also moved the TPS as that is an option with this TB and that did nothing. I’ve read that if I unplug my IAC and it fixes the idle problem that it means I have too much voltage to the TPS but idk how that helps me fix the issue.
Thanks for the responses. I wont be able to mess with my car for quite some time now as I just left for training but I’m leaning towards the issue being the huge change from 58mm to 75mm…. I will try what you suggested Krem12 but idk why my tps would be heat soaked now when it was working perfectly fine on my old throttle body. Maybe my throttle response wasn’t as good as I thought before 🤷‍♂️ If the size difference is the issue then I hope American Muscle will let me upgrade and pay the difference for BBK. Not holding my breath.
I would much rather make the SR TB and CAI work because that would be a pain and expensive to swap all that stuff out.
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 (americanmuscle.com)
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