North American Turbocoupe Organization



Really Cranky About Unruly Idle (UPDATE! 01-24-06)
t-bird88 Offline
Senior Member
#1
I set my idle according to the write up here, and now when the motor is warmed up the idle sticks. I have searched and came up with some conclusions, but nothing that I can consider as conclusive. I have the throttle set to about 700 RPM, the TPS is set at 0.94V and is new as of last January when I rebuilt the motor, and when everything is plugged back in, the idle comes back to where it is supposed to. But when the car is warmed up, it will stick between 2k and 2500, and sometimes around 3K. If I tap the throttle, most of the time, the idle will come back down. But when the motors temp is above 190*, the idle will stay at or above 2500. I even tried the turn off and restart the car while driving, and it will stay stuck at the above mentioned RPM. When I am on the highway and go to let off the throttle, the car acts like the cruise is on until I tap the throttle, then the car will start to slow down.

I have been putting up with this for almost a month now. I was hopeing that the computer would "re-learn" where the idle is supposed to be, but it has not. I even when so far as to take and very very slowly turn the throttle with my DVM attatched to see if there were any dead spots in the TPS. I went 0.01V at a time and it did not skip any numbers at all between 0.94V and 4.62V, up and down. I figured that if it was going to skip on the analog volt meter, then it would also on the DVM.

Any ideas on where I need to start on this fix. I am really tired of putting up with this problem.

Jim B :mad: .
Gunmetal Grey 88 TC!!!!
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Matt S Offline
Posting Freak
#2
I chased my tail on that since I bought the car. Multiple TPS, 2 times around on the engine sensors (ECT, IAT and all that). Resetting the computer. It would always come back.

Since I replaced my VAM in October it's happened to me ONCE..and after I tapped the throttle it went away, didn't even have to do the off/on thing.
I think others have noted a new VAM solved their problem also. Reman's from Rock Auto aren't that bad.
Sold it Sad*
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Import Killer Offline
Senior Member
#3
I forget how I got rid of mine, cuz my car did that too. After I put in a new coolant temperature sensor, it helped a lot. Try setting your idle to 1K. Thats where mine is and I havent had any problems.
1987 Turbocoupe
Painted sonic blue pearl
Ground effects w/S351 wing
17x9 Chrome Cobra Rs
255/45/ZR17 Kumho 712s
KYB suspension
MOMO shift knob and boot
K&N cone air filter, Gillis boost valve, T-3 turbo, ported intake and E6, A237 roller cam, MSD coil, Kirban FPR
Full 3" exhuast w/Ultra Flo muffler
Brute force clutch
White faced indiglo gauges
2 12" Rockford Fosgate subs and amp
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4cammer72 Offline
Posting Freak
#4
i just had the same problem and it was the cable for the cruise control. when i gave it a certain amount of gas the sleeve by the linkage would stick on the cable jacket. the plastic mount for the cruise cable had warped and was allowing binding.
88tc (sold) but keeping an eye out.
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t-bird88 Offline
Senior Member
#5
The thing that gets me is that before I set the TPS, it would not hang up. And now that I set it per the write up, it hangs, WTF????

I will check those other things that you guys mentioned and report back with my findings.

Jim B :mad: .
Gunmetal Grey 88 TC!!!!
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StangBolt Offline
Member
#6
OK, just an idea here, but are you absolutly certain it is a TPS issue? If the throttle blades are closed, and the TPS is not functioning correctly, I would not think the car would idle at all, much less at 2k rpms or better...
My first thought would be to check the throttle cable and associated linkage.
'02 Silver Lightning
'88 Silver/Blue Tbird TC
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grey88smokin Offline
Posting Freak
#7
I would double check the TPS, making sure it is on correctly and tight. Is the IAC clean ? I have yet to heat it mentioned. Get any codes ?
84 SVO 1C
08 MKZ
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JLockhart Offline
Member
#8
Quote:Originally posted by Matt S:

Since I replaced my VAM in October it's happened to me ONCE..and after I tapped the throttle it went away, didn't even have to do the off/on thing.
I can attest to the fact that low VAM voltage will trigger the IAC to kick in. Before I got my J3, I was running 42s with the stock computer and was messing with the spring tension and idle air bleed on the VAM. If I turned the idle air bleed too far out, I’d get the high idle problems. Also I would lose my decel fuel shutoff. I don’t know what the voltage threshold is though.

I would also try watching the tps voltage while driving to make sure it stays below 1v at idle after you have driven for a bit.
87 TC, T5, t3/t4, alky spray, 3" exhaust. 13.65 @ 102.75 on radials
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Pete D Offline
Administrator
#9
Even though it's a relatively new TPS, I'd check it for flat spots and drop out. I'd also check for binding linkage. My limited experience has been that turning the key off and having the idle be correct on the restart initially has usually been a bad TPS, however a bad TPS/high idle usually didn't respond favorable to goosing the throttle.

I agree on checking the codes. Since the problem seems to happen after warm up, I'll send you a file for checking the ECT, even if it doesn't set a code.
Pete Dunham


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dolphin1 Offline
Junior Member
#10
check the O2 sensor and make sure its working ok and check the O2 ground wire,my sensor broke internally and caused that a few months back.

Mike K
Mike

2 88's, one black & one white
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