Can anybody help me diagnose a high idle on a \'95 3.8 Stang?
If anybody is really bored and feels like reading down through this, I'd appreciate any advice or tips. I've been kind of stumbling around trying to figure out what's wrong with it. Below are a series of posts I have on Stangnet. They can't seem to figure it out. Just curious if anyone here might have a better idea. I know there's some pretty good tech guys here on [FJ]. Make me proud!
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Simply put, my g/f's '95 3.8 5-speed goes into a high idle (around 1,800) and won't come down. It just stays there all the time. I'm still learning about all the electronics on cars so bear with me. I searched through here but was not able to find anything.
Here's what I've tried so far (in no particular order):
(1) Checked for a vacuum leak: Nothing found. Vacuum system seems to be working properly.
(2) After reading the mannual, it said something about how the computer learns the idle. I disconnected the battery for about 20 minutes to reset the computer. Then started it up and let it idle for a few minutes. Then took it for a short 10 minute drive. All per the mannual...No change.
(3) Disconnected the TPS sensor. At least that's what I think I disconnected. No change.
(4) I also disconnected something else on the throttle body but I'm not sure what it was. It is the piece with the sticker on it that tells you not to adjust the idle screw CCW and to check the manual. No change.
(5) Removed the intake to make sure that there was no mechanical hang-up in the throttle body. Again, everything seems normal.
Well, I was working outside and it started raining so I gave up for the day. Any suggestions? I'm thinking maybe MAF next? Can I disconnect it to see if it will idle normally?
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And yes, all the tinkering I did was with the car hot. Its been doing this for a few weeks now. And apparently it just started all of a sudden. She noticed it when she got home one day and took the car out of gear. It was idling high and she tried to 'kick it down' like on an old carborated car. But nothing happened. It just continued to idle at around 1,800.
Just got off the phone with her. I had her check something out this AM. When the car is cold, it idles somewhere near the 'cold idle'. Somewhere just over 1,000. But once you drive it for a few minutes and it warms up, it goes back to the high 1,800rpm idle?
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The car is bone stock. Oil was changed about 3 months ago. I just did a tune up about 6 months ago. Plugs, wires, etc... And it has ran perfect up until this high idle problem. The reason we tuned it up was because it was getting some knock while going up hills in a high gear. And now that I think about it, after only 6 months, the knock has started to return?
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Re-checked all the vacuum hoses I could find an all seems OK. Also, disconnected the TPS sensor and it still goes into the same high idle.
I disconnected the IAT sensor and it didn't change. But it did throw a P0113 code (IAT).
On this car, the MAF sensor portion of the harness splits and goes to the MAF and the IAT. When I disconnect the IAT plug, it doesn't change the idle. But when I disconnect the whole portion of the harness (effectively disconnecting the MAF and the IAT), the idle goes back down to something more reasonable. Somewhere around 1,000. (You cannot disconnect just the MAF because of the harness design)
So I'm curious...Does disconnecting the IAT and MAF automatically put the computer into open loop? If not, maybe its the MAF sensor.
Just FYI - The open loop cold idle is slightly higher, by about 1,000, than the idle I observed when disconnecting the IAT and MAF.
Oh, and where the hell are the O2 sensors on this car? It was getting dark out and I had trouble finding them.
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Any Ideas, Tips?
