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90 XJ Idle Problems

megabyte5689

NAXJA Forum User
Location
Kansas
Hi, I'm new to the forum, I have a 90 XJ with 196,000 miles on it and recently its been acting funny, it idles really good when its cold and then idles rough once I start driving it around. The o2 sensor has never been replaced on it. I was wanting to know if that could be my problem, or my catalytic converter.
 
never has died, ya it will go low sometimes and then correct itself, it basically fluctuates. I always smell rotten eggs when I step out of the car, and my tail pipe makes a hissing noise the car sits their idling.
 
A faulty O2 sensor produced rough running, most noticeable at idle, on my 1990 4.0 engine. Gas mileage also suffered a bit. If you decide to change, try a search here- you need to get the right O2 sensor, and some 'universal' types won't work for you. I went to the dealership for mine. If your catalytic converter fails, usually the result is high back-pressure in the exhaust system, with the result that you have an obvious power loss. You may also be able to detect rattling from the loose insides, if you bounce the cat.
 
just get the one from any autoparts store, if its vehicle specific it will have an OEM style harness connector on it (three wire) should be 55ish dollars
 
I'm having the same issue..although when I let the gas up, the idle rockets down to about 100 rpm...and dies if you idle for more than like..10 seconds.. I have to use 2 feet to drive, always gassing it...But I don't have any hissing from the tailpipe..
 
a few things.

no, the universal type el cheapo O2 sensor will not work in a renix rig, it's a completely different kinds of sensor.

First things first
Check for vacuum leaks, a large vacuum leak will stall the motor at idle, and do weird things.
Find the TPS adjustment procedure, it's on here somewhere. Check that your TSP is in good working order.
Try cleaning your battery cables, in particular the grounds, make sure you check that ground strap to the head, it can look fine and then crumble in your fingers.
If all that checks out, I would take the IAC motor out of it's bore and clean it. Make sure the pintle doesn't fly across the room, and that it goes back in the bore the same way it came out.
Since you mention a hissing noise and rotten egg smell I would also check your cat. it sounds like it's hosed, and when they crumble inside they obstruct the exhaust pipe, causing all sorts of driveability issues.
 
I always look around the junk yard, the replacement Cats are about half the size as the stock OEM and are easy to spot. The typically last around 7 year or so. One that looks new is likely good.
Universal Cat's aren't that expensive anymore, I've seen them for around $60.
My idle fluctuated, it got better in stages, grounds (especially ECU and sensor grounds), cooling system in order, TPS adjustment, back to grounds again (harness splices), the intake/exhaust manifold and finally have a stable idle. It seemed to get better in increments, everything I did seemed to help a little. Finding a loose harness ground splice, seemed to be the last step to success.
 
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