bigwave

1998 Jeep Grand Cherokee Laredo, 4.0, auto
Can any of you wizards point me in the right direction with this. Jeep runs pretty well, the idle is a little rough but not too bad and it does not die. But the check engine light is annoying. I think this is all related and I've been looking for vacuum leaks, heater works correctly and I just replaced the thermostat, Ideas where to look?? The 1998 does not have a regular EGR valve.
Code read says:

B21 Engine is cold too long
B2E EGR system failure
U8F System Rich. R-Idle adap at lean LMT

Bustedback

The EGR code is a bogus code, but the too cold for too long code means the thermostat is stuck open and causing the engine to run rich.

bigwave

That seems more logical than some repsponses I've received. Do you by chance know how to test the wire sensor that comes off the thermostat? I'm sure it has an Ohm reading or ?? I did replace the thermostat a few months ago with a gates brand, I may be heading to the dealer to pick up the OEM mopar one.

Thanks.

Bustedback

I use a scan tool to read the data stream and a point and shoot thermometer, I the compare the two readings. I have been a professional mechanic for almost 30 years and have ohm tested sensors only a hand full of times. Call me lazy, but I always skip to the last line of the troubleshooting chart where it says "replace with known good part". So far it's worked for me all these years.

bigwave

Believe it or not that all makes since and my scan tool will read live and freeze data stream. I have a few point and shoot therms (mostly for teasing my dogs with the laser) but once in a while I use them for real.
I've been a shade tree mechanic for 30 years and a computer geek for even longer, I love precise instructions. Don't ask what computers from over 30 years ago, most people on these forums have never heard of them, unless they watch the history channel...... allot.

twinkiedooter

Call me an old lady but my 97 had some problems when I started her up. She would shudder for a few seconds and then run fine and dandy. I put a few ounces of Lucas Deep Clean into the tank that was 1/2 full and now she runs perfect when I start her up. I ran about 50 miles on the tank since adding the cleaner. No, I am not trying to push Lucas products but I thought something like a little clean out might solve your rough idling like it did mine. Your check engine light just MAY go out after using the Lucas. Good luck to you.

bigwave

I'm not afraid of trying "treatments" but I think they can be allot of snake oil as well as useful. I'm really leaning towards the parts store sold me a 165' therm when these jeeps like to be a bit warmer than that and I need to put in a 195' model.

I have some Lucas at home and will dump some in. We put it in the ATV's when we know they are not going to be ran for a month or 2. These jeeps do have the plastic or polymer tanks, which helps allot with keeping bad stuff out. Doing away with steel gas tanks on ATV's as well as autos has to be one of the best moves ever for people like us who keep our old stuff on the road.

bigwave

Okay, I have replaced the thermostat with a MOPAR oem 195' and I put in a new OEM Mopar temp sensor. The jeep is idling much better and the heater seems to be producing higher temps, which is nice right now. It was adequate before but now it seems to be a bit warmer. I was curious if the Check engine light would go off on it's own and so far it has not. It has been 5 days and 300 miles. Do you know, will the light go off on it's own if this was 100% the source of the CEL?
I will mostly likely hook my scan tool up to it tonight and clear the codes but, I was just curious from someone who actually knows this answer?
Thanks.