Random high idle - TCCoA Forums
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post #1 of 10 (permalink) Old 02-25-2016, 08:44 AM Thread Starter
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Random high idle

I have a 94 Mark VIII, I was at the bank yesterday suddenly the car started to run a little rough, I gave it a light rev and held it for a few seconds and let go but it didn't go away. Then when I was done I looked down and the car was idling at 1500. I put it in drive and drove home when I got home I put it in park and the idle was varying between 15 and 1800. I couldn't find any vaccum leaks. This morning I started the car and it idled around 1500for 5 mins and then it stopped and has been fine since. The IAC and EGR are new and shiney does anyone have any ideas?
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post #2 of 10 (permalink) Old 02-25-2016, 08:20 PM
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I have a 94 Mark VIII, I was at the bank yesterday suddenly the car started to run a little rough, I gave it a light rev and held it for a few seconds and let go but it didn't go away. Then when I was done I looked down and the car was idling at 1500. I put it in drive and drove home when I got home I put it in park and the idle was varying between 15 and 1800. I couldn't find any vaccum leaks. This morning I started the car and it idled around 1500for 5 mins and then it stopped and has been fine since. The IAC and EGR are new and shiney does anyone have any ideas?
If the new IAC is Motorcraft, I would get a new TPS as well. Not uncommon for both to go right around the same time. I was chasing that very same issue on my car (97 4.6 Thunderbird) and I did them both. Haven't had the issue since.

If the IAC is NOT motorcraft, get a Motorcraft one. All over Ebay for not too much money. Aftermarket/Third Party ones just don't seem to cut it.
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post #3 of 10 (permalink) Old 02-25-2016, 08:57 PM Thread Starter
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Ill be honest I have no idea who makes them. I bought the car back in June from a relative of the deceased owner. The kid couldnt get it running right, it turned out to be a bad coil pack, cossed plug wires, one bad wire, and a leaky intake manifold gasket. I noticed the new IAC and EGR when I took the intake off. Probably from them trying to get it running right. The TPS looks nearly impossible when the throttle body is on the car is it?
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post #4 of 10 (permalink) Old 02-25-2016, 09:13 PM
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Ill be honest I have no idea who makes them. I bought the car back in June from a relative of the deceased owner. The kid couldnt get it running right, it turned out to be a bad coil pack, cossed plug wires, one bad wire, and a leaky intake manifold gasket. I noticed the new IAC and EGR when I took the intake off. Probably from them trying to get it running right. The TPS looks nearly impossible when the throttle body is on the car is it?
I've never done one on a DOHC, but on my 2v it's a piece o cake.
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post #5 of 10 (permalink) Old 02-26-2016, 11:37 AM
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Similar thing happened to my 94 Mark engine (High idle rev, reluctant to shift to 4th). Turns out rain water kept dripping on the TPS making the sensor short out. It would run fine when I would swap it out with a dry sensor or let the car sit and dry out for a few days. I finally made a duct tape poncho and wrapped the sensor. Try the TPS sensor and look inside the electrical connector for moisture. If it's wet, swap the sensor and try to build it a little shelter.
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post #6 of 10 (permalink) Old 02-26-2016, 05:23 PM Thread Starter
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Thats interesting because the car is running fine today, meanwhile it poured for the last 2 days.
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post #7 of 10 (permalink) Old 02-26-2016, 06:06 PM
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I've never done one on a DOHC, but on my 2v it's a piece o cake.
A 94 dohc has an intake similar to the 94-95 tbirds; everything is buried at the back of the engine, under the wiper cowl.

You pretty much have to remove the wiper cowl to do anything to the TB.

And it's in the middle of the car, low.

The cake is a lie, lol.
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post #8 of 10 (permalink) Old 02-26-2016, 07:15 PM
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A 94 dohc has an intake similar to the 94-95 tbirds; everything is buried at the back of the engine, under the wiper cowl.

You pretty much have to remove the wiper cowl to do anything to the TB.

And it's in the middle of the car, low.

The cake is a lie, lol.
So you're saying GLADoS designed the older Ford intake manifold?
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post #9 of 10 (permalink) Old 02-27-2016, 08:07 AM Thread Starter
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I figured I did have to take the cowl out again, I also took the hood off when I did the intake manifold for more light and space. I definitely used High-Tach on the upper and lower manifold gaskets I just hope I didnt use it on the throttle body and IAC too. I got to do something soon, on cold start up the engine surges to 2000 rpm and stays there. Then I put it in gear for a couple seconds and back into park and it stays at 1000 rpm.

I have the Actron scanner with the Digital display, but I feel like its not sophisticated enough to allow me to test individual parts. I know with say a Modis or Verus you can check TPS voltage and even graph it. Is there anything out there for our cars? I looked at the "New Generation Star Tester" and theyre really expensive on eBay. I was hoping to find some kind of laptop program, or a better quality stand alone scanner. It would be nice to be able to test the TPS before I took it all apart, and see what the IAC is doing.
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post #10 of 10 (permalink) Old 02-29-2016, 01:42 AM
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I had something similar a few years ago, ended up being the PCM. Here is the thread that describes my issues.

http://forums.tccoa.com/7-engine-4-6...ough-help.html
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