Rough Idle Problem - '89 Jeep Wrangler YJ

Hey fellow Jeepers, I have a problem that has been plaguing me for the last 6 months. I bought my '89 YJ in November of 2002, and ever since
I got the engine to run, I have had a rough idle problem.
Jeep is an '89 YJ - 2.5L 4 cyl. - TBI.
Symptoms: - Idles rough between 1000 and 1400 RPM's. - Runs smooth and great above 1800 RPM's and has plenty of power. - Possibly runs rich at idle. - Consistent miss at idle. - Does NOT stall.
Things I have to done to try and fix it: - New spark plugs, wires, and rotor. - New O2 sensor, MAP sensor, Coolant Sensor. - Tested and verified MAT senor, TPS sensor. - Fixed all leaky vacuum hoses. - No vacuum leaks. - PVC valve is working. - Used fuel injector cleaner 3 times in gas tank. - Removed injector and cleaned manually with throttle body cleaner. - Removed Throttle body and cleaned it (all passages inside clear) - New air and fuel filters. - Compression test yielded readings around 140 to 150 for each cylinder, which are in the lower range, but still ok.
Here is the real weird thing.. I unplugged the O2, Coolant, and MAT sensors, and it ran the exact same!!! It seems to me the computer is running in some default safe mode and not even using the sensors (at least some of them). Maybe the computer is defective??
I can't read the engine codes because it is has the AMC computer ('87 to '90), and I don't want to take it somewhere to get the computer diagnosed every time for $80.
Any ideas or help would be greatly appreciated! Thanks
-Brent Bogrees
More specs and pictures of my Jeep are on my website: http://www.chrr.ohio-state.edu/~bogrees/html/Jeep.html
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Ok... depending on the setup, you sure could be describing a blown purge valve on the charcoal canister. (gas tank vent)
You say you have a PCV. Check the plumbing on it for a second line that either comes right off the PCV itself or T's off it along it's route to the intake manifold.
If you have this second line, it will go to the canister. At idle, pinch this line to the canister closed.
If the idle starts to mellow out, the canister is worn out.
Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's
Brent Bogrees wrote:

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Thanks for the quick response guys. Here is the update..
Opie, the O2 sensor I bought has the wiring and clip, so I don't think that is the problem.
Mike, I don't have a second line coming off the PCV as far as I can tell. I tried pinching all the hoses that went to the canister and nothing changed.
You did give me a good idea of where to start looking however. The hoses and wires around the canister (right below the battery on the firewall) looked a little messy, so I figured I would organize them and replace any hoses that were old. The starter relay has a lot of wires connected to it, and low and behold, one had corroded and broken off. I fixed this immediately, and got the mess organized. I don't know where the fixed wire goes to yet, but I am going to test and find out (maybe a sensor?).
Here is the BIG thing I noticed while tracing all my vacuum lines again. On the top of the intake manifold (close to the firewall), there is a one-inch rubber hose with a tiny hole in it, which points toward the firewall. I hadn't noticed this before. I also had a small plastic black vacuum hose coming out of the firewall that didn't go anywhere. I plugged the two together, and the engine calmed down right away!.
I still have a slight miss, and I am attributing that to valves for the moment. I am hoping that it will go away after I do a partial rebuild in a couple of months, or when I decide to throw in a Chevy 350 and say to hell with it!
Thanks for the help.
-Brent '89 YJ '94 XJ

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I forgot to add that I also replaced the EGR valve, which was rusted shut.
-Brent
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Brent, Just went through this with my 88 YJ 4 cyl. You said you replaced o2 sensor. Did you use a 3 wire generic?? I tried 2 of them and they did not work. Had to go to Jeep and get the factory one with wiring and clip. Problem solved here.
Brent Bogrees wrote:

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replying to Brent Bogrees, Schbaum wrote: I had an 89 YJ. Acted the same way. It turned out to be a pinched fuel return line. It got pinched where the return line goes between the body and frame by the rear wheels left side.
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