North American Turbocoupe Organization



Introduction and Idle Problem (Long Post)
Turbobird96 Offline
Junior Member
#1
I was thrilled when I found this forum a few months ago. I have owned a Turbo Coupe since 1996, and had to figure out many problems by myself. I have three of these cars now - two 88's and one 87 parts car. I think I have experienced every problem these cars can develop, but this one has me stumped.

Ever since I bought my White 88 (see signature) it has had an idling problem. The idle was erratic at times when the car was at operating temperature (idle always increasing), but never idled up above 1200 RPMs. Then at about 180,000 it blew a head gasket (the rear oil passage began to leak), so I changed the head gasket and installed a re-manufactured head (the old one cracked). Ever since I replaced the head the idle problem has gotten worse. Here are the things I have done:

Replaced the VAM with an aftermarket one from Advance in 2000- since then computer will occasionally throw a 42 code (thanks to this site I now know it is not due to the O2 sensor!)

Replaced the TFI and PIP, distributor looked good with no play in shaft

Replaced IAC and TPS and adjusted it per instructions from this site

Replaced ECU with a known good one

Checked for vacuum leaks (replaced overboost sensor, cruse control module and all vacuum lines), now no leaks when tested at the vacuum port coming off the intake.

Checked and cleaned all engine compartment grounds and the ground at the computer

Doing all these things helped the car idle correctly about 70% of the time when at operating temperature. When the car is cold or barely warm it will idle correctly. If you are cruising on the interstate and exit it will idle correctly. It mainly acts up when doing around town driving. In stop and go traffic if you take off and have to stop again in a short distance the idle will begin to increase. With each stop and go it will usually increase a bit more, but never going above 1700RPM. If you turn the car off and immediately restart it the idle will be correct. When it is acting up I have gotten out and disconnected the IAC and it has dropped down to 700-800 RPM like it should. Nothing is sticking in the throttle body either. I also disconnected the vacuum line to the EGR valve and it still acted up. I really am at a loss now as to what the problem is. Sometimes the car will run correctly all day long, even in stop and go traffic. It seems to just depend on its mood! It is not outside temperature related either. It will act up at random on warm or cold days.

Sorry about the long post, but this problem is really getting to me and I wanted to give you all the whole story. Hopefully I have not forgotten any of the details. I have been searching these forums for months but still have not found the solution to my idle problem. After 15 years of fighting this I really want to get it solved!
1988 White Turbo Coupe, 5-Speed 227,XXX miles, no mods.

1988 Black Turbo Coupe, 5-Speed (was Auto), 129,xxx miles, no mods.

1987 Black Turbo Coupe, 5-speed parts car (too far gone to restore)
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84TBirdTurbo42 Offline
Senior Member
#2
I had a very similar issue with the same code that ended up being a throttle body to intake gasket. Fought with it for the last 5 years before. Figured it out.
Chris Perry
1984 Ford Thunderbird Turbo Coupe. Dead, NY rot killed her
1986 Thunderbird shell, swapping parts from the 84.
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Pete D Offline
Administrator
#3
Welcome to the nest.
Any other codes besides the 42?
Pete Dunham


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Turbobird96 Offline
Junior Member
#4
No other codes than the 42. I have been getting a random code 42 since I owned the car. The PO decided the best way to eliminate that code was to remove the check engine light bulb, LOL.

That's a great suggestion 84tbird. I will check that out. I have a feeling it is going to be some off the wall problem that is hard to find, since I have done all the obvious things already. When I replaced the head I put on all new gaskets except for that one. I never unbolted the throttle body from the upper intake.

Thanks for the welcome Pete. This forum is a godsend for anyone owning these wonderful but temperamental cars!
1988 White Turbo Coupe, 5-Speed 227,XXX miles, no mods.

1988 Black Turbo Coupe, 5-Speed (was Auto), 129,xxx miles, no mods.

1987 Black Turbo Coupe, 5-speed parts car (too far gone to restore)
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zbird Offline
Posting Freak
#5
I definitely would check for a vacuum leak around the intake somewhere. I use intake cleaner to spray around the areas suspected and listen for a change.
Dom Z
88 T/C med grey. 140 MPH Speedo, Kirban FPR, Gillis valve,Tripminder, K&N.
87 T/C Silver, Auto (project Daily driver)
99 F150 4x4
14 Ford Escape 2.0L Turbo
IF YOU DRIVE A FORD YOU DON'T NEED A GOODWRENCH!!
88 T/C http://www.youtube.com/watch?v=ZihO_D1FLCE
87 Silver http://www.youtube.com/watch?v=_dVU5axnb...ature=plcp
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Paulie Offline
Banned
#6
One of the best ways to check for vacuum leaks and boost leaks is with SMOKE. Have the engine smoke tested for leaks if you suspect one. The idle hunting is a problem with fords for a very long time. Not only 2.3 engines i might add. One of the problems is the TPS if it does not work properly the idle will HUNT. Another thing about the IAC is it does not close all the way when not commanded. You explained in your post that removing the plug reduces the IDLE speed And corrects it. That tells you that the ECM is raising the idle speed. A vacuum leak would not FIX IT SELF. But i would still check for leaks anything is possible. Sounds like a computer issue not getting the correct signals it is looking for for proper idle speed. I personally do not use the stock IAC. I use the 5.0 plastic valve that has 100% air shut off. The TC IAC has a metered bypass air system. This should not be an issue on a stock motor. Also is the cam OK and not FLAT. Sometimes a flat cam can cause this. I have seen this once before. Either way the fact that when you disconnect the plug on the IAC basically points to a computer glitch that is raising the idle. Believe it or not some coupes suffer from this and its very hard to fix. The ecm is very Sensitive. Also watch your Spark plug wire routing. Also make sure the plug wires are good and not breaking down. The wires can send out RFI and do strange THINGS. Also the TPS should be tested and do a complete sweep. Several times to confirm its operation. The TPS can cause this and i normally use a SCOPE to check for Noize on that sensor. The TPS would be where i would look very carefully. Thanks
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Martin Offline
Senior Member
#7
My Auto had the same or similar symtoms, twice now. I replaced the ECT and it cleared up. IT could possibly be the cause. THe first time I changed it wothout draining the coolant, fast switch. THe second time I drained the coolant down a bit, and cleaned out the port and passges best I could as sometimes the coolant passage gets blocked up and the ECT does not get a real coolat temp reading.
Stock 87, no mods, Black with the grey interior.
Boost High, Fly Low
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Turbobird96 Offline
Junior Member
#8
I have replaced the TPS three times over the years and the problem remained. On the current new TPS I checked the sweep with a multimeter and it checked good, but I did not check for noise with a scope.

The cam is good. I changed it when I replaced the head, and the motor runs very well with plenty of power. It also had this idling problem to a lesser extent with the old head, and the cam looked great on that one when it was removed.

When I unplug the IAC I usually have to rev up the engine a bit before I pull the plug from it. If I don't do that 9 times out of 10 the motor will die. Is this normal?

I think this car has had an idling problem for a long time. The PO had tried to adjust the TPS and cranked the idle screw on the throttle body as far back as possible before (before the butterfly valve bound on the throat of the throttle body).

I may give it a tune up this weekend since it wouldn't hurt to do so. Heck, maybe I will change the upper intake gasket and throttle body gasket just to rule it out. I don't know if this is related or not, but the car also likes to ping when it is warm outside (above 70) and under full boost. It has done it since the day I took ownership of it, and have never been able to correct it. I replaced the turbo, gave it a tune up and adjusted the timing (with the spout out) and then gave up. The only way to get around it is to run octane boost or don't dog it when it is warm. This is with it in the premium mode, not regular. I will not do this in regular mode.

I also suspected the computer was getting false signals, which is why I replaced the VAM and TPS and ECM years ago. After that did not work I checked the grounds thinking that could be the problem.

Thanks for all the suggestions so far and please keep them coming. I want to squish this idle gremlin once and for all! What kills me is the parts T-bird I have never had this problem. My brother drove it for years before it was retired. The TPS was adjusted wrong and the PO beat the living daylights out of it and abused it, and it idled at a steady 1000 RPM all day long with no electrical problems!
1988 White Turbo Coupe, 5-Speed 227,XXX miles, no mods.

1988 Black Turbo Coupe, 5-Speed (was Auto), 129,xxx miles, no mods.

1987 Black Turbo Coupe, 5-speed parts car (too far gone to restore)
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Turbobird96 Offline
Junior Member
#9
Martin I just read your post. You were writing it as I was drafting my previous post. While I have everything apart doing the tune up I can certainly clean the passages and change out the ECT. Couldn't hurt at this point. You guys are going to make my weekend a busy one!
1988 White Turbo Coupe, 5-Speed 227,XXX miles, no mods.

1988 Black Turbo Coupe, 5-Speed (was Auto), 129,xxx miles, no mods.

1987 Black Turbo Coupe, 5-speed parts car (too far gone to restore)
Reply

Pete D Offline
Administrator
#10
I was thinking possible ECT issue. They don't always set a code.
The pinging probably indicates lean for some reason (air or vacuum leak, fuel delivery problem) Check the VAM and IC hoses for cracks and leaks. I mean take then off and squeeze then to open up hidden cracks and holes.
Pete Dunham


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