North American Turbocoupe Organization



High Idle/ Sticking Idle
RocketshipChair Offline
Member
#1
After curing all the vaccuum leaks in my car (loose bolts on intake manifold and broken hose on boost guage). My car's idle became much more normal about a notch under 1000 RPM. It stayed this way for about one day. Then the next night it would end up idling high (1500-2000 RPM). I replaced the IAC and the TPS sensor the next day. I reset my idle using the article in the technical article section. My idle with the IAC unplugged was set to 750 RPM. My TPS set to .94 volts. The car drove the best it's ever driven for about a day and half. Now it's developed a strange problem. It idles fine about half the time. But the other half of the time the idle will stick at 1500 or 2000 RPM. Now here's the weird part, if I just gently tap the gas pedal the idle goes right back down to a notch under 1000 RPM. I'm totally stumped right now. What do you guys think? So far I'm thinking I've got a defective TPS.
Andrew
88 Turbo Bird 5 spd no mods
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Not B Anymore Offline
Administrator
#2
Either a faulty tps our a sticky throttle cable would be my guess. This is what mine was doing a few months ago. I replaced the throttle cable and it's been fine ever since.
Brian Leavitt
'86 TC 5-Speed -- MS2x w/COP | 83 lb. injectors | T3/T4 50 Trim Stage 3 .63AR | Full 3" Exhaust - No Cat | Motorsport FMIC | Ranger Roller | Ported E6 | Walbro 255HP | Kirban | 20psi | 120-amp 3G | 8.8" 3.55 rear | '03 Cobra Wheels
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Jeff K Offline
Administrator
#3
Also look for broken / damaged throttle return springs. Check for any carbon buildup at the throttle plate hanging it open.
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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RocketshipChair Offline
Member
#4
I cleaned and lubed up the throttle cable. Its a little bit worst and a little bit better now. The idle doesn't stick high as often now but when it does it's more likely to stay stuck until I restart the car. I ordered a new throttle cable from carquest as ford no longer has any available. The return springs seem fine to me and hopefully they really are because nobody makes replacement springs. I might have a spare throttle body kicking around if worst comes to worst.

On a side note, I decided to take a year or two off from working towards my EET degree. I'm going to complete an auto technology program this year. That way I don't have to pay other's to fix my TC and I can make some decent money working at a dealer while I finish my EET degree.
Andrew
88 Turbo Bird 5 spd no mods
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Jeff K Offline
Administrator
#5
High idle that returns to normal after a restart is often due to TPS volts set too high so it occasionally goes over 1.0 V closed throttle or failing TPS that goes over 1.0 V closed throttle.
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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TurboCoupe50 Offline
Posting Freak
#6
Set TPS to .85v and try that... Betcha it fixes your problem...
1988 Turbo Coupe331 AOD

1972 Comet GT

1969 Fairlane Cobra 428CJ 4-Speed
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RocketshipChair Offline
Member
#7
Set the TPS to .84 volts after still having issues with .94 and .90. Same issue. I also looked at the return springs on my spare throttle and they look in exactly the same as the one in my car. I should be picking up my new throttle cable tomorrow.


At this point I'm pretty convinced its a bad tps. As soon as the idle sticks if I shut off the car and restart it or just tap the accelerator quick and hard the idle goes back to normal.

Is there anyway to test if a new tps is deffective?
Andrew
88 Turbo Bird 5 spd no mods
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Pete D Offline
Administrator
#8
Andy, as far as I know you would have to put the new one in and then check it like you would a used one.
Pete Dunham


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Jeff K Offline
Administrator
#9
^^^^ What Pete said.

If you have any old analog VOMs around, you could monitor TPS volts while driving and at closed throttle and see if TPS voltage spikes over 1.0 V at closed throttle. DMM probably wont work as response time / display refresh time might be to long to pick up glitches.
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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RocketshipChair Offline
Member
#10
Just wanted to post an update saying that I'm in the process of solving my high idle and wanted to document my discoveries.

Though the original TPS was part of my high idle problem, the real issue was caused by my thottle body sticking. This was being caused by the shaft of plate bimding on the housing and weak return springs. The shaft has been cleaned up and lubricated but I'm still looking for a source for new return springs.
Andrew
88 Turbo Bird 5 spd no mods
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