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: