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Old 01-09-2011, 12:40 PM   #1
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Default 1999 Cherokee idle problem

Hi guys,

I am new to the forum and new to jeeps as well. I just bought a 99 cherokee sport with the 4.0L and Auto trans. It has 194k on it and has a really rough idle and sometimes stalls. It runs great when you are on the gas. I drove it to the auto parts store last night and did a decent burnout so it's not down on power, just won't idle correctly. I cleaned the IAC, put in new plugs, checked for vaccum leaks and fixed one (now the heater controls work!), I took the map sensor off and applied some vaccum to it and got the idle to change with different amounts of vaccum so I'm assuming it's probably ok. I unplugged the 02 sensor and nothing really changed so I'm assuming it might be bad but I thought there should probably be a check engine light if it was? What do you think I should check next? Any help will be very much appreciated.
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Old 01-09-2011, 01:09 PM   #2
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I have sort of the same problem but mine hasn't stalled yet. I was told that it was my fuel injectors being clogged. Ive added some injector cleaner to my tank yesterday but haven't drove around enough to see if has helped any.

You may want to add some seafoam to a tank of gas and see if that helps. If not take out your injectors and soak them in carborator cleaner for an hour or so and see if that helps.
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Old 01-09-2011, 07:11 PM   #3
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1. Finish your tuneup with new plug wires, cap, rotor. And be sure you are not running BOSCH plugs as the 4.0 doesn't do well with them

2. Did you thoroughly clean your THROTTLE BODY when you cleaned your IAC. If not, go back in and do so with throttle body cleaner.
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Old 01-09-2011, 10:11 PM   #4
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Quote:
Originally Posted by tjwalker View Post
1. Finish your tuneup with new plug wires, cap, rotor. And be sure you are not running BOSCH plugs as the 4.0 doesn't do well with them

2. Did you thoroughly clean your THROTTLE BODY when you cleaned your IAC. If not, go back in and do so with throttle body cleaner.

I did clean the whole throttle body but I haven't finished the tuneup yet. I'm getting a whole new throttle body for free within the next couple days with tps and iac on it so I think I'll throw that on there and also do the wires and cap and rotor at the same time and hopefully that will help. I got the carpet cleaned up today so that was a major improvement at least
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Old 01-12-2011, 12:18 AM   #5
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Well didn't have time to get to the parts store before they closed tonight but I got the throttle body with IAC, TPS, and Map and put it on. Started it up and immediately got a check engine light. I pulled the code and it was a po122. I checked the wiring and even disconnected the clockspring connector just to rule that out. None of that made any change. I put my old tps back on and cleared the code and the check engine light no longer comes on but it still idles rough at about 750 rpm. I sanded the contacts in the distributor cap and rotor since the parts store was closed but didn't make any difference. I noticed that at an idle the exhaust sort of pops at the tail pipe. I crawled underneath and the muffler actually seems warmer than before the cat? I'm almost wondering if it is plugged? Exhaust all looks original. Just seems weird that it would run fine under load and at higher rpms if the exhaust was plugged.
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Old 01-12-2011, 12:22 AM   #6
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finish the tune up you could just have a spark plug miss firing at idle
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Old 01-13-2011, 03:38 PM   #7
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Quote:
Originally Posted by freegdr
finish the tune up you could just have a spark plug miss firing at idle
I put on a new cap, rotor, and wires last night and no change. I put some injector cleaner in and was letting it idle for about 20 minutes and decided to check all the fuses and put my hand down on the passenger floorboard ( I have the carpet out) and it was so hot it actually burned my hand! Also I revved the engine up to about 4500rpm and the was a bunch of black crap on the ground behind the exhaust. So I'm thinking possibly plugged cat?
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Old 01-13-2011, 03:45 PM   #8
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sound like its running rich possible o2sensor going bad
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Old 01-13-2011, 03:48 PM   #9
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Default check this out

http://wiki.answers.com/Q/What_does_code_P0122_mean
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Old 01-13-2011, 07:12 PM   #10
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Yeah the old plugs were black. I'm gonna run it into my buddy's work tomorrow and plug in his scan tool to check everything out. He also says he can check the temp of the cat to make sure it isn't plugged and we are gonna try some combustion chamber cleaner to clean out any carbon.
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Old 01-14-2011, 07:16 AM   #11
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Black plugs indicate a rich mixture.

Suspects would include a bad map sensor, coolant temp sensor, oxygen sensor, incorrect fuel pressure due to a bad pressure regulator.
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Old 01-14-2011, 05:39 PM   #12
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Well I was on my way to my buddy's work to check out the jeep and put a window in the block. Yay!
Click the image to open in full size.
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Old 01-15-2011, 06:00 PM   #13
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I have the same problem. I had a code 132 saying o2cencor or fuel regulator. It's apparently running rich but hasn't given me black plugs. Btw. Where is the fuel regulator located?
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Old 01-16-2011, 09:50 AM   #14
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As far as I know, the fuel pressure regulator is part of the fuel pump assembly and is located inside the fuel tank. You can test the fuel pressure by hooking up a gauge to the schrader valve on the fuel rail.
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Old 01-16-2011, 10:00 AM   #15
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On 97 and newer, the pressure regulator/ fuel filter is a combination piece that sits on top of the tank. It connects to the pump through the top of the tank. It's kinda easy to remove and you don't even have to open the tank to so it. You do have to drop the tank to replace it though and the filter/regulator will set you back a little over $100.

I just replaced mine.
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