North American Turbocoupe Organization



IAC question
TheBullSchmidt Offline
Member
#1
ive been trying to figure out y my car wants to idle at 2500rpm i reset the tps to the proper voltage and checked the vam and its within spec but when i plug the iac in and restart the car it idles at 2500rpm. i find it hard to believe its the iac because its brand new. any other ideas? or could i just leave it unpluged seemes to run fine with out it.
1988 T-Bird TC auto, all stock
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Jeff K Offline
Administrator
#2
Is the new IAC a cheapo off brand or a Motorcraft? What was your closed throttle TPS voltage? Does it return to the same value every time throttle is closed?

It will run fine without the IAC operational, but you will loose cold start fast idle, decel dashpot function, and load idle correction (AC on, high electrical loads, etc).
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
05 Taurus SEL Duratec daily driver
04 Taurus Duratec (wifes car)
02 Pontiac Grand Prix GT
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized
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TheBullSchmidt Offline
Member
#3
tps was set to .94 and yes it returns to .94 when the throttle is closed. the iac is what ever you get from autozone so yes probably a cheap off brand. im just at a loss dont know what else to try...
1988 T-Bird TC auto, all stock
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Jeff K Offline
Administrator
#4
Could possibly be the cheap junk AZ sells. Maybe grab a few Motorcraft IACs from the JY, clean them up and try them. If every one does the same thing, check the IAC to PCM circuit for a short to ground, which would keep the IAC fully open all the time (I doubt this is the problem, but worth checking).
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
05 Taurus SEL Duratec daily driver
04 Taurus Duratec (wifes car)
02 Pontiac Grand Prix GT
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized
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TheBullSchmidt Offline
Member
#5
thanks for the info... just wondering im not really good with electronics so how would i check for a short with a voltmeter?
1988 T-Bird TC auto, all stock
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Jeff K Offline
Administrator
#6
Disconnect EEC 60 pin connector and IAC connector. Key off. DMM on ohm setting. 1 lead to IAC terminal that is NOT the red wire (I forget the color off hand) and other to any ground (engine, etc). DMM should show very large resistance (10 k ohm or larger).
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
05 Taurus SEL Duratec daily driver
04 Taurus Duratec (wifes car)
02 Pontiac Grand Prix GT
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized
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OU812MACH1 Offline
Senior Member
#7
on (some) not all cars u have to drive them over 35 mph for 20 seconds for the IAC motor to reset it self...
o4 mach-1,white,4at 1 of 169 ,MAC air filter and x-pipe, SCT tune / o9 BMW 328 M-SPORT, white, 6at/ 87 Turbocoupe ,white,4at,KIRBAN afr,GILLIS boost valve,Garrett/SVO T3,cold air,3" STINGER down pipe and tail pipe, DYNOMAX ultra flow stainless muffler, Walbro 255L fuel pump,cleaned and flowed injectors,STINGER BOV, built A4LD trans w/all
4x4 Explorer guts, K245/F57FA torque converter.
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TheBullSchmidt Offline
Member
#8
ok jeff leave it to the non electronicaly oriented guy to have a dmm with 4 ohm settings i set it on the 20k setting and it read 16.4 i tried another iac off a car that ran properly but no luck. ive tried driving the car around and it didnt seem to fix anything...
1988 T-Bird TC auto, all stock
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Pete D Offline
Administrator
#9
It you turn the engine off and then restart, does it idle OK for any time at all?
Pete Dunham


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TheBullSchmidt Offline
Member
#10
no idle goes straight to 2500rpm...
1988 T-Bird TC auto, all stock
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