Idle issues, help needed

[mansep2]

Help my idle seems to have gone nuts, at first it ran just fine then on a run down the coast the idle suddenly decided to run at 1200-1500, I replaced the IAC and MAP sensors as they were some of the only ones that had not been replaced from the original 95 firebird donor car but to no avail.

I started the car today and from cold idle was at 2000, and would not reduce then all of a sudden the idle shot up to 2700 so I turned the car off, on restart it was still in the 1500+ range.

Yikes what's the scoop here and what can I look at?????????


by the way this is a new long block with ancillaries from a donor 95 3.4 V6 out of a firebird and it is in my 1973 MGB roadster

[Purple pit]

Try a new throttle position sensor. When they go bad they make a high idle.

[walterdude]

Sounds like a BIG air leak to me,,, Lower Intake gaskets can really mess with the idle.... With the engine running you can spray carb cleaner all around the area and listen for any changes... You can also use an UN-lit propane torch to check for air leaks...
Of course check out all the Vacuum lines... They get old and crack easily....
Good luck,,,,
Tom B...

[AutoWiz]

take a piece of cardboard and lay it flat across the face of the throtthe body while the engine is running. If the motor stays running, then you have a gross vacuum leak, If the motor stalls, then maybe you have a failing iac, bad wiring, tight throttle cable, or bad tune. clean looking swap, btw.