Shortly after starting my XJ, maybe a minute or so the Rpms are all over the place, up and down, it cuts out, stalls, and occasionally backfires. But after a few minutes it clears up and runs great. Any suggestions/help would be greatly appreciated.

Thanks
Jason

 

I guess I should clarify a little more. This occurs with and with out the a/c on. It only occurs about 50% of the time and when the jeep sets overnight or 39 minutes or so. Time doesn't seem to matter. It's more of a stalling issue, almost as if the fuel system is bleeding back into the tank and sucking in air but there are no fuel leaks that I can find.

 

Sounds like you have to do the poor man's prime. I have have to do that too. Next time you start your jeep turn the key to the on position and listen for the fuel pump to pressurize the system. Do this 2-3 times then start it and see if that works. If that works then that is an indication of the fuel pressure regulator on top of the fuel pump not holding pressure. It was ideling bad because of lack of fuel pressure and air in the line.

 

Poor man primes generally only helps with a hard start, not a running issue after starting.

I'm experiencing a similar problem with mine but I know I have a bad head gasket leaking into cylinder 4. The running issue clears up after about 30 seconds.

Another possible cause could be a leaky injector flooding the intake and causing an extra rich condition until the fuel clears out.

You may also want to clean the throttle, check connections for the IAC and TPS, unfortunately there are plenty of causes for the sypmtoms you are describing. just got to start eliminating them

 

I have ordered a new TPS and IAC. I tried cleaning the IAC yesterday but it didn't help, it actually made the issue worse.

 

I bet that alone will fix your issues. I tried to do the STEAM clean of the Intake Manifold etc that I saw was popular. I must have did it wrong because it messed up both my IAC and TPS. That produced the symptoms you described. The one that really fixed the issue was the TPS. After I put in a new TPS, it at least stopped the High IDLE and RPM spikes. I tried to clean the IAC and that really didn't fix my RPM fluctuation issue. I probably damaged the IAC. so I may have to get a new one.

 

I hope so. The funny thing is that once it warms up there are no more issue. It runs great. It runs great for the first couple of minutes after started, then goes into the stalling, low idle, rpm spike, than back down to low rpm almost dies, and repeat. It does this 3 -5 times than it's good to go. I cleaned most of the connectors yesterday and applied connector grease. fingers crossed.

 

Hmm mine was similar but it started with symptoms right away when I turned on Vehicle. I never left it on long enough to even see what it would do when warming up. It actually scared the crap out of me lol.

 

So I have a 1994 Jeep Cherokee with a 4.0 and when I leave for work I have to stop at a stoplight and then it dies. When it's hot it don't die and it dies only when the a/c is on and anyone help tell me what u thank it is

 

Unplug your O2 sensor and see if it runs better, if it does replace it. Mine was doing the same thing and that was my problem. I just fixed it today.

 

I also vote to check the O2 sensor. Sounds like when the computer starts listening to it (which is a few minutes after startup, when temperature comes up) it is misleading the computer regarding air/fuel mixture. It may be working better after it gets nice and hot, which could explain why things smooth out.

 

Thanks I will try that today

 

Last tuneup with plugs, wires, cap and rotor?

Ever clean the throttle body and IAC?

 

I cleaned the throttle body a couple of times, even took it off of the manifold and cleaned it. While it was off I took the IAC off and cleaned it as well. I bought the Jeep this year from a MD that parked it at a airport and only drove it when he flew in to work at the local hospital. It sat most of the time and only had 78K miles on it (He bought it new in 99). He had records of the oil changes but none for the plugs, wires, caps or rotor. the Cap and wires look new and are probably not factory, but thats all I know.

Which O2 sensor should I unplug? I believe there are two, an upper and a lower.

 

Upper.