OK, let me explain the original problem and I am hoping someone can benefit from my experience on my 99 WJ with the 4.0L......
About a month ago, my wife explained that the Jeep started "revving" high and wouldn't slow down. She thought it was going to get away from her and it scared her. It did finally die back down to idle though. I thought she was going nuts.....until it did it with me in the car with her one day about a week later.
About two weeks ago, it started running erratically and died several times like it wasn't getting fuel or spark. It also developed a habit of feeling like the tranny was slipping or bumping when going over a slight rise or float on the interstate. Kind of like it was catching up with itself.
Needless to say, I thought the tranny was going out, I had a manifold leak, and that the fuel pump was going out. Time to trade in the ol' Grand Cherokee......??
Not quite. I changed the plugs (had double the recommended gap
), and cleaned the IAC valve as recommended on this forum. It seemed OK at first, but last week, it did the same thing again. And again. Back to the drawing board.
It also threw codes, PO123 (TPS Pedal Pos Sensor A Circuit High Input) and PO121 (A Circuit Range)
Enough is enough. I went to AutoZoned(out) and got both the TPS sensor and the IAC valve for a grand total of $101. I installed them both today and have had zero problems after 50 miles of driving. It is much smoother and doesn't have any problems now. It would hardly run yesterday.
Thought I would pass this on. I recommend changing them both as PM if you have over 100K on your car. Cheap insurance from a lot of headaches!!