I have been having problems with my 97 XJ since i bought it. It started idling rough a couple days after i bought it. It was blowing black smoke out of the exhaust. after about a week if would not even stay running. I tried new plugs, wires, cap and TPS with none of these helping. It was slowly getting worse and read it could be crankshaft sensor. Replaced this and it started up and ran better but still had a rough idle. I drove it around the block a few times and all of the sudden when giving it gas it would not hardly go. Acted like it was not getting fuel. Once over 2000 Rpms it would go better but not much power. I have checked the fuel pressure, replaced 02 sensor also.
Does anyone have anymore advice? I am tired of spending money and not getting it fixed! Have an appointment this week to get it looked at but if i could trouble shoot before that would be great!
Any advice would be appreciated!

 

You want to troubleshoot it now after throwing a bunch of expensive sensors at it? Blindly replacing sensors is no the way to diagnose a problem on a computer controlled engine. Keep that appointment with the shop. I suspect a problem with the MAP sensor or a possible cracked header before the upstream O2 sensor. You have something that is giving the PCM some bad info and the PCM is adding fuel to compensate for what it thinks is a lean condition.

 

I actually had been all over threads for about a week and a half looking and trying different things people had recommended. I tried cleaning the throttle body, IAC and TPS sensors. I had taken it to a shop to have them read it and the said the system they had would cut out around the crankshaft so they were not able to properly ready it. They said it could be the crankshaft sensor so that is when i tried that. It was a night and day different for about 5 minutes. I had an appointment last week to get it looked at again but had to reschedule. Just thought i would ask around for some information on things to try without spending any more money until i got it looked at.

I have read that you need to reset the system after replacing sensors also, is this true? I had tried that after the TPS but not after the CPS or 02 sensor.

Thanks for the input.

 

The most frusturating thing is I bought it and drove it 250 miles hope with no issues at all. Within a day or 2 it started idling bad and just went down hill. So have only had about 3 total days of driving since i bought it 2 1/2 weeks ago!

 

You should do a compression test on it. If you find a low hole or two, do a leak down test. Then you can rule out a mechanical problem if those two tests check out ok.

 

What are the codes that you are getting. Assuming you had the code read? That is the best place to start. This would at least point you in a direction to look. You said you checked the fuel pressure. What was the pressure that you got? We also need to know what size engine do you have?

 

I just recently had an issue with my check engine light and the idle not working correctly when left for roughly a minute or more on idle in park is would go down to almost 0 rpm and 1000 and up and down repeatedly til I restarted it , than same issues give or take the time . my issue was the o2s fuse under the hood its a small 15 amp fuse , not saying its your issue , yours could be much worst . in my case I ripped off the cat o2s sensor on my driveshaft , reinstalled a new o2s engine light off , idle fine , day later same issues , I replced the fuse and she sits at like 6 700 rpm on idle now . hope this is the issue , because its simple and cheap . good luck

 

I am actually not getting any codes. I read something on another forum on how to check to make sure your CEL is working and i did the test and i believe it has either been removed or the bulb is out... I checked the fuel pressure at an idle and it was 41 which is what i read it should be. I have the 4.0 but i believe it is out of a 96 cherokee. I replaced the upper 02 sensor when i replaced the CPS and that made it stop smoking (it would only smoke a little and had some soot in the water coming out of exhaust). After replacing CPS it started and idled but was a little rough (not bad). I took it out and gave it some throttle a few times to try and clear out some of the soot and it didn't seem to have a lot of power but would still take off. After a few minutes of driving when i would step on the gas it would just sputter a bunch and not take off. You could slowly go and it did ok but any hard acceleration it just fell on its face.
Also since then the first time i start the engine it starts up then dies immediatly. I restart it and give it a tiny bit of gas and it stays running. I am hoping tomorrow they can diagnose the issue but still makes me wonder what the heck is wrong with it.

Thanks for the replies!

 

Go to any auto parts store and have the codes read. That should have been your first step.

 

Sounds like it could be a vac line issue... Might/might not throw a code. I can send some pics of common failure points if you cannot find them via search.

Edit:

Also, have you checked your battery terminals? Get a wire brush, disconnect pos and negative, and get them completely clean. If they are in really bad shape go ahead and switch them marine terminals. THIS SOLVES A BUNCH OF XJ GREMLINS!