North American Turbocoupe Organization



Random high idle ?
t c mike Offline
Junior Member
#1
First time posting. 1988 Turbo Coupe auto trans. 47,600 miles. Sometimes it idles @ 2 grand after a drive. AIC has been replaced....any ideas?
This is my 2nd T C . Had an 87 in the mid 90s, dual exhaust & bypassed the waste control. It RAN GR8 for an auto car.
Any thoughts & info greatly appreciated !!!!!
mike
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Jeff K Offline
Administrator
#2
Welcome to NATO, Mike!

Was the new IAC a Motorcraft part or aftermarket junk? Aftermarket IACs are ALL JUNK. Motorcraft are the only ones that work properly.

Check closed throttle TPS voltage. If closed throttle volts are over 1.0 V you will get a hanging high idle. Best to set closed throttle TPS volts to around .94 V.
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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t c mike Offline
Junior Member
#3
Big Grin 
(06-13-2020, 12:21 PM)Jeff K Wrote: Welcome to NATO, Mike!

Was the new IAC a Motorcraft part or aftermarket junk?  Aftermarket IACs are ALL JUNK. Motorcraft are the only ones that work properly.

Check closed throttle TPS voltage. If closed throttle volts are over 1.0 V you will get a hanging high idle.  Best to set closed throttle TPS volts to around .94 V.

Thanks Jeff !! Authentic FORD iac.  Will check the tps voltage. Also the car was only driven 1700 miles in 4 years and had a small 700 cca battery that needed a battery tender. Hoping that driving it & having a new 850 cca battery may
solve some issues too.  LOVE my car !! Have had a 53 Ford Vic. for several years & had flathead fever.....don't miss it at all.  Smile
Have a GR8 day.mike
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Tedybear315 Offline
Junior Member
#4
(06-13-2020, 02:00 PM)t c mike Wrote:
(06-13-2020, 12:21 PM)Jeff K Wrote: Welcome to NATO, Mike!

Was the new IAC a Motorcraft part or aftermarket junk?  Aftermarket IACs are ALL JUNK. Motorcraft are the only ones that work properly.

Check closed throttle TPS voltage. If closed throttle volts are over 1.0 V you will get a hanging high idle.  Best to set closed throttle TPS volts to around .94 V.

Thanks Jeff !! Authentic FORD iac.  Will check the tps voltage. Also the car was only driven 1700 miles in 4 years and had a small 700 cca battery that needed a battery tender. Hoping that driving it & having a new 850 cca battery may
solve some issues too.  LOVE my car !! Have had a 53 Ford Vic. for several years & had flathead fever.....don't miss it at all.  Smile
Have a GR8 day.mike

I'll keep an eye on this one as well.  Our '88 does this as well and we've yet to finger it out.  It'll just start holding the RPM at idle @ around 1700-2100 RPM.  It's not doing the auto transmission to many favors.  I've got the wife to shut the car off while sitting in reverse or drive with it under load.  Otherwise it'll take off like a rocket!

S-
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RC Martin Offline
Posting Freak
#5
I went through this same thing for years and it magically went away though I don't know what one thing cured it. I now have a 2k cold idle that settles down to 900 hot, I call that good and normal. On cold starts sometimes it stumbles and dies, always restarts and never dies again rock solid. *shrug*

Across throwing parts at it, I did new plugs .030, wires,cap, rotor, new cleaned IAC, new TPS dialed in, timing at stock (never ran better for me with some advance), new 195F superstat, EGR delete, new exhaust.
Thunderbird Turbo Coupe, Bright Canyon Red TuTone, Desert Tan Interior; 1 of 7 in this combo in 1984 according to Marti.  1 of 13,361 TCs in 84.
   Rebuilt, 3-Angle Valve Job, SYB37 "OE/Small" Slider Cam
   Full 3" Stinger Exhaust to Flowmaster 40, Gnari FMIC/Recirc/BPV, MBC @ 18psi, RF-E6 Manifold, Remote-Mount TFI, PC1 and Flowed 35# Injectors, Inline Walboro 255HP, Kirban AFPR
   Rebuilt Suspension -- KYB & Energy Suspension
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84TBirdTurbo42 Offline
Senior Member
#6
a friend of mine, who has been a Ford tech since beyond the dawn of time, maybe earlier... told me that was the biggest bitch of these cars back in the day. I have a suspicion it might be vam related, as iirc at least on the 86 and older cars, that the intake air temp is measured that way. There are days my car will idle normal, other days its hunting like crazy.
Chris Perry
1984 Ford Thunderbird Turbo Coupe. Dead, NY rot killed her
1986 Thunderbird shell, swapping parts from the 84.
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t c mike Offline
Junior Member
#7
(06-18-2020, 08:52 PM)84TBirdTurbo42 Wrote: a friend of mine, who has been a Ford tech since beyond the dawn of time, maybe earlier... told me that was the biggest bitch of these cars back in the day. I have a suspicion it might be vam related, as iirc at least on the 86 and older cars, that the intake air temp is measured that way. There are days my car will idle normal, other days its hunting like crazy.
THANKS to everyone !!!! 2k rpm has dropped to 1500 and then only once in a while. I too shut it off in gear. Once i shut it down, it doesn't do it again....wierd. It gets serviced next week by an "old time" mech. who knows these cars. He too is thinking tps & iac.....maybe vam.
mike
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Jeff K Offline
Administrator
#8
You can check VAM volts by tapping into the BK/W and W/BK wires at the 4 terminal VAM connector. With throttle closed you want the volts under .5 V. If much above that you can get high idle. You can adjust this by removing the 1/2" or so diameter plug on the top output (to turbo) side of the VAM. Drill a hole maybe 1/4" deep in the plug, screw in a sheet metal screw and pull the plug out using a vise grip on the screw. Use a long Allen wrench (I forget the size..... maybe 3/16" or so) to adjust the bypass air, which in turn changes the closed throttle VAM output volts.

I discovered this years ago when I replaced my VAM and immediately had a high engine hot idle speed (1800 RPM or so).
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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t c mike Offline
Junior Member
#9
(06-19-2020, 02:34 PM)Jeff K Wrote: You can check VAM volts by tapping into the BK/W and W/BK wires at the 4 terminal VAM connector. With throttle closed you want the volts under .5 V. If much above that you can get high idle. You can adjust this by removing the 1/2" or so diameter plug on the top output (to turbo) side of the VAM. Drill a hole maybe 1/4" deep in the plug, screw in a sheet metal screw and pull the plug out using a vise grip on the screw. Use a long Allen wrench (I forget the size..... maybe 3/16" or so) to adjust the bypass air, which in turn changes the closed throttle VAM output volts.

I discovered this years ago when I replaced my VAM and immediately had a high engine hot idle speed (1800 RPM or so).

Thanks Jeff !!! 
Can i charge the bat. with cables connected ?
What about a battery tender ?
Thanks in advance ..again.Sure do appreciate N A T O & all the info !!!!!!!!!!
mike
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Jeff K Offline
Administrator
#10
No problem charging the battery with the cables connected. I have done it many times with no issues, even on our newer OBDII junk with 10x as much electronics in them as the TC has.

Battery tenders / float chargers are a good idea for a car not driven much, especially if you live in a climate with COLD winters like I do. Harbor Freight has them for extremely reasonable prices. I dont drive my Tbirds at all in the winters here as the roads are encrusted with salt for 4 or 5 months a year. I do start them up every few weeks and let them run until up to temperature, jack up the rear with my floor jack and run the trannies thru the gears several times to keep the trannies and rear ends lubed up.
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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