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Jeep Idle/Stalling issues

post #1 of 31
Thread Starter 
You guys have helped in the past, so of course I came back again. My 99 Jeep Grand Cherokee with the 4.0 has been acting strange. It starts in the morning, but when it does, it doesn't sound right. It almost seems to have low idle. In addition, when I drive it and slow down or come to a stop sign, the idle fluctuates between 1,000 and 400, sometimes falling as low as to stall out. This has happened to me twice already, and once in the high speed lane on the highway when I had to slow for traffic. I was thinking a few things: I have cleaned the throttle body and installed a new gasket. Because the idle fluctuates, I was thinking either the Idle Air control or the Throttle Position Sensor. Before I just go out and spend allot of money, I was hoping someone could give me some ideas. As always,
Thanks again!
post #2 of 31
Start with the battery. If the PCM is not getting the correct voltage because your battery is not holding around 12 volts or more (even if it is intermittent) you would have the kind problem you described. Could be a host of other things, sensors, IAC, plugs missing, etc. Start with the battery/charging first.
post #3 of 31
Good advice on the battery. I have a Wrangler with the 4.0 engine and it will not idle correctly if the battery is weak. If you've ever left the lights on and needed a jump to start it, you'd see the symptoms that you describe.
post #4 of 31
Do the obvious first:

Measure the voltage across the battery, should be ~12 V. Open up the air filter housing, it may need to be replaced or cleaned. If that's ok, i would do the fuel filter...whens the last time you did spark plugs and wires? Sounds like it's not getting enough fuel...
post #5 of 31
throttle position snesor can cause idle issues as well as the crank position sensor
post #6 of 31
The Throttle PS would cause more problems in accelerating really, not the idle problems. It can have a dead spot that causes it to shift weird, like the trans is going bad almost. And the Crankcase PS usually either works or doesn't work. Since this is an intermittent problem I doubt it's that. I would say if it's not battery related check your plugs and spark. Could still be the IAC (Idle Air Control)
post #7 of 31
post #8 of 31
First thing I would do is to CHANGE the fuel filter. INSPECT the Air Filter as well.

The EGR valve is also quite easy to check, as is the PCV valve.

Pull the sparkplugs and note the color of each. WHEN was the last time they were replaced?

post #9 of 31
Re-reading the post, nobody has addressed the Vacuum system, and a vacuum leak would cause exactly the problem you describe. Check all vacuum hoses, one could have easily slipped off.

If it isn't the vacuum, my money is fuel supply.
There are guages that measure both vacuum as well as fuel pressure, but unfortunately, only professionals have them!

post #10 of 31
HR, how did you make out? There wasn't much here that wasn't diagnosed, I'd like to know what the culprit really turned out to be.
post #11 of 31
Thread Starter 
hi guys,
sorry i have not responded sooner. the battery is brand new. I can't do anything with the fuel filter because it can't be replaced. it is a lifetime filter inside the tank. I changed the plugs just because it is easy to do. i did speak to a buddy of mine who works on jeeps and he suggested the TPS and the IAC, which I have just need to install this week. once i get thos done, i will let everyone know. also, i did check the vacuum connections, and they were all good. hopefully, this will solve the problem and no more stalling on the highway! happy new year to all! I will let you know what happens within the week!
post #12 of 31
Yikes a lifetime filter?

What if you get a bad lode of fuel with 10k?

This would be the first non changeable fuel filter i heard of since i left the busness.. dont suprise me thought but dont lake sence.

My bet (1 beer) is still the egr. I would not go around changeing sencer and such without prpper testing ,,,it can get costly
post #13 of 31
Most of the time it is the IAC motor, second is the EGR valve.
post #14 of 31
Thread Starter 
Hey all...I wanted to follow up with everyone since I installed the sensors....driven three hundred miles and the Jeep has never been idling issues, no stalling far, so good. thanks for all the help!
post #15 of 31
TPS and IAC?
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