I recently purchased a 98 Cherokee Sport. I have replaced the spark plugs, wires, cap and rotor. Before doing this it started to act like it was getting very little gas when trying to go. It also has a rough idle once in a while. It doesn't do this all the time. Very speratic. I have put in fuel addatives in the fuel and to see if it may have been a fuel issue. I also used some spray sea foam and ran it through the throttle body to see if that would help. It still has a speratic rough idle.
What could possibly be causing this?

Thank you for all of your help and/or advise.

Here are a couple of pics. Of my recent purchase.

 

Look along the intake manifold , down below the throttle body for vacuum leaks at any of the connections or vacuum plugs

 

Just solved this on my jeep a few weeks ago. First thing was my PCV valve on the back of the valve cover. then 2 weeks later it was my Upstream O2 sensor. Hope it helps

 

Sounds pretty close to what was happening to my jeep it ended up being the upstream O2 sensor.

 

I did notice one elbow at the front of the intake manifold that was rotted. I will look again just to sure I didn't miss another leak.
Thank you

 

I tried getting a PCV but, was told they didn't have them. I will check another store. The upstream 02 sensor was supposedly just replaced but, I will get under there to verify.
Thank you.

It's wierd, it didn't happen at all when I took the 40 minute ride home but, has happened everyday since. Almost feels like the fuel is getting cutting off.

Thank you again for all the help.

 

Could it have just been a tank of bad gas you finally cycled out. This just leads me to believe you have a bad injector.

 

Hahaha no problem Some places have it listed as a PVC Valve. I got mine at the dealership for just over $15. Oh and they might ask if you mean the ccv valve but that is the one on the front of the valve cover that connects to your air filter. Only replace that one when you get oil on you air filter.

 

Okay, so there is a PCV on the back of the valve cover? I didn't find any other vacuum leaks and it doesn't look like the O2 sensor was replaced. It definitely shouldn't look like it does if it was replaced with a new one. I think he may have just reset the check engine light and the O2 still may be back.

As for the bad gas, I would have thought with the Seafoam, Heet Fuel stabalizer and later a bottle of Techron by Chevron, I would have thought the fuel issue would have been solved. I also sprayed about half a can with the straw into the throttle body, while it was running. Took about a good 3-5 minutes and then took it out for a good run.

Today when I started it, it was acting up but, when it warmed up it was idling better but, you could still hear a miss.

Thanks again for all the help.

 

Have you checked out the Crank Position Sensor (CPS), and fuel pressure (weak fuel pump)?

 

Is there a way to test the Crank Pisition Sensor and what about the fuel pressure? Would the O2 Sensor still be the problem even though it's not throwing a code? I would think a code would come up. It's very speratic when it does it. Today it did it on start up and ran fine when it warmed up but, the last times it happened, it was already warmed up.

Thanks again for all the help and/or advice.

 

O2 sensor will not throw a code. I know its stupid

 

Okay, so it looks like the next purchase is a PCV and an upstream O2 Sensor. I found the O2 sensor cheaper on Partstrain.com last night. I will see if they list the PCV as well. Shouldn't take too long for them to come it. They ship pretty quickly.

Thanks again for all the help.

 

did you bother to check the fuel injectors? probably sensors though

 

First off I want to thank everyone for the quick help and advice.

I finally replaced the O2 Sensor and what a difference it made. While it was on the lift to change out the O2 Sensor, I found a vacuum hose that was rotted back by the fuel tank. Got the O2 changed and drove it back to work. Drove much better. When I got to work, I grabbed some extra hose that I had and put in a new piece to replace the rotted one. Started it up and shortly after the check engine light went out. Drove it after work about 40 minutes away and back home again and rain much better. Still has a little bit of a rough idle but, not sure if these really have a smooth idle anyway. But, it's definitely not as much as what it was and definitely not while I'm driving like it was doing before. I have to see if I still have the transmission silenoid code but, plan on changing the filter and fluid this weekend which one of the guys at the parts store said may help with that. We will see.