Bad idle please help me???
 

Hi there i have an 86 gt, and when i start it, it idles real high like at 2000 rpms then in about a 1 min it will go down to 1500 then around 1000, then it will runn like that then about every few mins it will go up then down and keep doing that. i chaged the Spark plugs and i Chosed the Boush PLatnium 2 with the 2 sparkers on it. the wires are Aem and they look pretty new and i just put on a new MSD blaster 2 coil, what do you guys think it could be thanks alot.
Ernie

Check your TPS sensor and make sure it is set right. Also, you may want to check your o2 sensors, and your idle speed control solenoid. Hope this helps.

Chris

Here are a few articles that may help you.

How to fix a hunting idle...

Idle Problems
A common problem in the EEC-IV controlled 302 Mustangs is a hunting idle. This is an idle which fluctuates in RPM up and down and up and down....It can be very annoying.

There are a lot of tricks people use to try to fix this problem. Most of them don't work.

One common trick (that doesn't work) is to try to "fool" the EEC-IV into thinking the engine is still in warm-up. This is accomplished by installing a low temp thermostat and/or removing the ECT (engine coolant temperature) sensor. It fails when the HEGO sensors detect a too rich fuel mixture, and the EEC-IV compensates by leaning the mixture out. Now you're back to the hunting idle.

The EEC-IV is programmed to idle the car at 672 RPM. Incorrect throttle plate position is ithe primary cause of the problem in most cars. To adjust this, back the screw out until it no longer touches the throttle plate stop. Insert a 0.010 feeler gauge between the screw and the stop and turn the screw until it touches the feeler gauge. Then turn the screw another 1.5 turns. Then adjust the TPS (throttle position sensor) to 0.98V.

I had this problem for the longest time in my car and tried the steps above to correct it. Unfortunately, I didn't have a voltmeter handy so I used trial and error with the TPS adjustment.

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How To Adjust TPS
"Muscle Mustangs & Fast Fords"
April 1993
The throttle position sensor is one of those things that falls into the category of "computer stuff" that makes a big difference and is easy to deal with, but average people like us would never know about. Without the proper adjustment, the throttle position sensor (TPS) will give the computer a false reading as to the exact throttle opening. A false reading will limit wide open throttle performance (something we definitely don't want). A voltage reading must be taken using a digital volt/ohmmeter (DVOM) with the Key On/Engine Off and with the Key On/Engine Running. A Radio Shack DVOM, part No. 22-185A, works well for this job.
The TPS is located directly on top of the throttle body and is adjusted by loosening the two phillips mounting screws and swiveling the sensor until the highest reading is found. It may be necessary to elongate the holes with a small file to achieve the desired reading.

The spec range for Key On is from .88 to 1.0 volt; shoot for the .97 to .99 volt. With the engine running, the voltage should be no higher than 1.05 volts.

Incorrect Throttle Position Sensor (TPS) voltage will result in reduced performance. The best way to take a TPS voltage reading is by using two safety pins through the wires coming from the sensor. The positive lead is attached to the green wire, while the negative goes to the black wire. Always ground the meter through the sensor's black wire. This gives a direct, and more accurate ground into the computer.