High idle

GatorGlassRon

Registered User
Bought a 90 sc with a slew of mods, and cannot get this sucker to idle normal. Think it has a magnum powers tb. Idles at 1700 and does not drop at all. Unpluged iac and killed motor instantly. Removed iac and taped up holes and will not idle at all. Bought new iac from auto zone and idles worse at 2200 rpm all the time. This really sucks. Guy I bought it from says it always idled fine, untill he killed the battery by leaving interior light on before he shipped me the car. Trying to at least get it decent, before I drive 6 hours to see David. Any suggestions???
 
Its not throwing a code, I even checked all vac lines and zip tied most of them. I do not get it. The tb is adjusted so the set screw is all the way backed out and closed..... So where would the air be getting in??
 
This is what the car has done to it:


Fully built made 310RWHP – 425RWTQ on Dyno Jet @ 20Lbs. Boost
Rebuilt 3.8 liter V-6 Supercharged
Rebuilt 5 Speed B&M Ripper short shift kit
3.27 Limited slip differential
Cobra cross drilled big brake kit
Steel Braided brake lines
New master cylinder, brake booster
Engine:
Ported and polished heads w/ MLS head gaskets
Magnum Powers MPx stage 3 super charger with coated rotors and raised top
Magnum Powers 10% overdrive blower pulley, 15% overdrive crank pulley and BHJ aluminum harmonic balancer
SCP HD supercharger belt tensioner springs,
Magnum Powers Spearco front mount intercooler
Intercooler fan
Raceware aluminum radiator w/ electric fans
Tig welded 3” to 2.5” to 3” Flowmaster exhaust
95’ cerami-coated bored& ported manifolds
Magnum Powers 85mm throttle body
SCP cold air intake
60 lb. Siemen’s injectors
85 mm C&L MAF
255 LPH fuel pump
95’ fuel tank for better exhaust flow
SCT Tune chip
 
Yes, and between shifts, the rpms will rise. It was really bad with the auto zone iac. I put the stock ford one back and now its 1700. Its weird, because if you are driving and come to a stop light it will idle at 1700, if you bog it while in gear I can get it to 1100. But soon as you tap the gas,.....voooom and back up to 1700.
 
Its either the IAC or you have an IC tube leak or leak around the blower somewhere

The IACs on these cars are notorious for their diaphragms cracking and raising the idle hella high
 
No, I only have the tb that is on the car (85mm magnum powers). I have the stock IAC and a new one from Auto Zone. How do I check for a blower leak? I will check the intercooler connections. I just bought this car off the classified section on this forum. Did not expect this BS
 
it is possible both IACs are bad even though one is new...I have seen that before...
There is a Allen wrench plug in the MP inlet that you can pull out and pressurize the system that way with air compressor...It is like a reverse compression test...
You should hear a little air coming out of the TB and maybe you might hear some leaking through the valves
 
Also I am not sure if the adjustment screw position you mentioned is correct...and the adjustment screw is not supposed to be adjusted to change idle...it should be done through the ECM or you can throw things out of whack
 
My idle adjustment screw on my MP 85mm TB looks to be all the way down in the hole...

also I would check the throttle cable and make sure it isn't hung up anywhere...I also got my accelerator pedal stuck on my carpet a couple times

Just throwing it all out there
 
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