1990 YJ Idle rough/Stall Problem - JeepForum.com
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post #1 of 10 Old 09-29-2008, 04:14 PM Thread Starter
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1990 YJ Wrangler 
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Location: Titusville, FL
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1990 YJ Idle rough/Stall Problem

I just purchased an 1990 YJ Jeep wrangler and it idles pretty rough unless it is warmed up. I have to press the gas petal when i start it for it to turn over. It seems to idle rougher when I am in gear (with the clutch petal fully pressed in) than when I am not in gear. Once i run it for 10 minutes or so it seems to idle ok (no stalling) however still wont turn over unless i give it some gas. Should I adjust the idle or is it possibly a vaccum leak? Any advice? Thanks.

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post #2 of 10 Old 09-29-2008, 04:22 PM
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1990 YJ Wrangler 
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Is it a 4 or 6cyl?
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post #3 of 10 Old 09-29-2008, 04:29 PM
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1991 YJ Wrangler 
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dont have a carb, so i cant speak from experience. but the need to press the gas pedal to turn over is something i would bet is quite common amongst the carb crowd. as for the rough idle...timing maybe? i know one of the gurus will chime in sometime

'91 YJ 4.0 3/4'' Brandon Booms 31/10.50 BFG AT Herc'd CJ dash/tailgate CJ5 seats 4KCs cracked windshield

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post #4 of 10 Old 09-29-2008, 04:36 PM
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1990 YJ Wrangler 
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If it's a 6 cyl, then it's a carb and in that case leanr to love this website http://home.sprynet.com/~dale02/list.htm

If it is a 4cyl, then there are all different issues possible with diagnosing the problem

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post #5 of 10 Old 09-29-2008, 07:21 PM Thread Starter
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Its a 4cyl, fuel injected
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post #6 of 10 Old 09-29-2008, 11:09 PM
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At this point, it could be a gazillion things wrong. First, check all your vacuum lines, and their connections. Then, check your plugs to make sure the gap is all the same, and they are burning at about the same color. If you haven't done it for awhile, change your fuel filter and make sure you have adequate pressure at the rail. Some of the other things to check is the wiring connections and confirm they are seated properly. Once this is done, give us a report and we'll work on other things.
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post #7 of 10 Old 09-29-2008, 11:13 PM
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1992 YJ Wrangler 
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stuck choke?
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post #8 of 10 Old 03-19-2013, 09:13 PM
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Dirty carb

Just cleaned mine out like it said and she runs great .Found out its easier to take carb half off .Also you can take out them tubes that clog,thats the key. Yj is back in action.Running better than ever!!!Doing it the way it said is not bad if you don't drop anything.STEVE
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post #9 of 10 Old 03-20-2013, 07:46 AM
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1989 YJ Wrangler 
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Welcome to the forum!

Just purchased then do the basics:
Start with the basics: tune up for sure. Plugs, wires, cap,rotor, and the fuel filter. Clean the throttlebody.
You are throttlebody injection so the computer controls idle. There are several adjustments that are essential for the TBI when you replace a sensor. If you don't have a multimeter get one. You need it to setup and troubleshoot. At idle the coolant temp sensor (The YJ has 2, the one in the rear is strickly for the temp guage the other one on the manifold is the one for the computer) is the primary sensor for cold idle and sets up the calibration unil it goes into closed loop after it warms up and uses the other sensors.

Download the service manuals in this thread:

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post #10 of 10 Old 01-18-2016, 10:41 AM
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1990 YJ 4cyl. Rough idle

I have 1990 Jeep Wrangler 4cyl. 125 thousand miles 25 years old. I encountered the same problem and it took some doing to correct.
The good news is that there are parts available for this year model jeep, and second, it all required very little labor to achieve the "Fix".
First off I had issue with knocking valves when starting specially in very cold weather.
Fix: Drained oil and changed oil and oil filter THIS WAY. 3 1/4 Quart of 5w30 oil, (not 10w40) and one Quart of RIZLONE OIL . (Jeep takes exactly 4 1/4 Quarts of oil including the oil filter.) Knocking stopped instantly when starting in very cold weather. Next oil change in cold weather, always 5w30 oil. (Hot weather 10w40 oil)
Next issue was rough idle .
Fix: I replaced the EGR valve. That took care of most of rough idle and amazing speed power in all gears. However it still idled (less) rough and it was "Hiccuping" at 40 50 and 60 miles per hour. At this point I changed the OXYGEN SENSOR. This ALMOST completely eliminating the rough idle and NO MORE HICCUPS.
Next I changed the spark plugs,spark plug wired rotor and distributor cap.
It runs perfect now. The big expense was the EGR Valve $99 and OXYGEN sensor $55.
I hope this helps.
E mail me. manny
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