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post #1 of 7 (permalink) Old 09-04-2006, 08:33 AM Thread Starter
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Low idle

Ok I have a 95 thunderbird, 4.6L no mods, Have replaced IAC with new, have voltage to IAC but idle is very low and no difference between plugged in and unplugged, what could be my problem, can blow air through intake tube when IAC is disconnected. Don't know where to go from here. The car idle too low to lift foot from gas when cold. any help would be great.
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post #2 of 7 (permalink) Old 09-04-2006, 10:30 AM
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Have you cleaned the MAF?

Jay

These are highly engineered precision vehicles, the first step in diagnosing the problem is to strike the suspected offending part sharply and repeatedly with a blunt object, then re-test.
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post #3 of 7 (permalink) Old 09-04-2006, 01:42 PM
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Uh, the car is actually supposed to stall when you disconnect the IAC. Did you replace your old one to try to fix this problem? Maybe your new one is bad as well.

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post #4 of 7 (permalink) Old 09-04-2006, 06:24 PM Thread Starter
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think it is fixed.

I removed the new one which was supposed to fix the problem, tried cleaning it checked all passage ways for any blocks and put it back together, it isn't too hard to do on a 95 with a magnetic pick up tool. Ran the same figured screw it and just turned the idle stop screw (the never mess with headless bolt.) and tried raising the idle and it miraculously fixed the IAC. I looked at the IAC and am thinking that if there is too much vaccum or the IAC is weak the IAC can get sucked into a closed position and not be able to open and by opening the throttle just a touch, it realeses enough vaccum to allow the valve to operate. Does that sound like a possiblility or maybe just luck?
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post #5 of 7 (permalink) Old 09-04-2006, 07:35 PM
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Well, you shouldn't have touched that screw, lol. Sure screwing it in further is going to increase you idle. You have just opened the throttle plate by screwing it in. But now you have thrown off the minimum air setting for the engine. That screw is set from the factory to a calibrated position that lets in a certain amount of air when the throttle body is closed. The computer's programming is based on this calibration. Now that you have altered it, you will be letting in more air than you are supposed to be and you will have a tendency to run lean. The fuel trim tables in your computer are all going to end up changing and your injectors are going to have a longer duty cycle than they should have. Your engine may very well run fine, but the computer isn't going to be running on its optimal programming mode.

Now about your thoughts of the IAC. If the IAC was indeed "weak" (this would mean that the solenoid is essentially broken) it wouldn't work right at all. Even under no vacuum conditions, if the PCM were to specify a certain duty cycle for the IAC, it would be completely incorrect and your idle would be totally erratic.

You really need to fix the real problem of the idle for everything to be perfect. When you replaced the IAC, did you reset the computer so it can relearn everything? Something that simple could be the solution to your problem. The fact is that throttle return screw needs to be in its calibrated position, and the idle of your engine should noticeably change or the engine should stall when it is idling and you unplug the IAC. In addition, your MAF sensor should be working properly to correctly measure the incoming air charge. Adjusting that screw may get you by, but it's not the cause of the problem unless it was previously tampered with and for some reason was backed off from where it should have been, but that's an unlikely case.

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post #6 of 7 (permalink) Old 09-05-2006, 08:38 PM Thread Starter
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The screw had vice grip marks on it and now when I unplug the IAC the goes to an amazingly low idle, like just barely above stalling, I used the tube from the IAC to the intake to feel if it was opening or closing and after I turned the screw out a little the IAC tube drew in air when the AC would cycle or it was put into gear and it seems to have a steady constant idle. When I replaced the IAC I did reset the PCM with the fuse trick and the unhook battery way. Still nothing helped till I just tried adjusting the screw. I turned it very little. I will clean the MAF once I get a set of anti-tamper torx bits. Someone in the past may have gone and for some reason lowered the idle, or something along those lines but now it works like a champ and I don't know what else to say...
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post #7 of 7 (permalink) Old 09-09-2006, 04:03 PM Thread Starter
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Idle problem is back, have cleaned MAF, made engine run better but idle same, reset EEC, no difference reinstalled original IAC not change. I found that with the tube to the IAC off when i give it throttle it draws air down the tube? what could this mean? Could there be a blockage in my manifold and if so how could I get it out? I'll have to get a can of that spray TB cleaner that you spray with the engine running, I'll give that a try.
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