fafafofi

When I'm sitting at a light, my RPM's will fall down to about 500. It'll start to spit and cough to where it almost dies so I'll have to rev it up so it doesn't die. When the light turns green and I try to accelerate, it hesitates and feels like it isn't getting any gas to it. The check engine light keeps reading o2 sensor.

I've replaced both o2 sensors, MAP sensor, IAC, TPS, spark plugs and cleaned the throttle body.

What's wrong with my baby?!?

Abovetimberline

Have you checked your fuel pressure? also you 02 sensor is coming in because you still have a misfire,as long as the 02 sensors see unburnt fuel,it will show up,it does not mean the sensor is bad,it means it is outside its voltage range.

jeepfreak82

map sensor could be reading incorrectly also, it does affect the fuel mixture and idle speed also so it is a thought

Willys55

Do you have acess to a scanner?
Which O2 code do you have?

Do you ever get a code P0171? (engine running to lean)
With the scanner you could look at the engine data and see what the block learn data reads.........LTFT Long Term Fuel Trim maxed out would inditacte a lean condition.
With more information I could be of more help

fafafofi

The code I'm getting is a high voltage code, P0138 I think. The MAP sensor is 2 days old from Advance but I haven't checked the fuel pressure. Is that something I can do in my driveway or take to a mechanic? A couple peeps on jeepforum said it could be my CPS so I thought about trying that next.

offroadnut36

Your fuel ballast resistor could be burnt up.

97XJMopar

Just hook a fuel pressure gauge to the schrader valve on the fuel rail. Advance, Oreilly's, and AutoZone all sell a little kit with gauge, braided hose, and fittings to adapt to most fuel rails.

fafafofi

What readings am I looking for? Do I hook it up and then start it up to get the correct psi?

4.3L XJ

Yes. It should be a constant pressure. I think it is betwen 45-51 psi.

97XJMopar

Autozone says:
44-54 PSI (Pounds per Square Inch)

Position the ignition switch and the A/C system in the off position. Install a fuel pressure gauge to the vehicles fuel rail or fuel pressure test port. Confirm that no leaks are present, and visually verify the PSI reading on the gauge with the ignition in the on position.

fafafofi

Thanks. Speaking of the A/C. I haven't had any idle problems while the A/C is running because the rpms are always higher at stops. Does that give anyone an idea of what might be happening?

2000xjRed

Hey i have not seen anyway say hey maybe its the coilpacks, so hey i am willing to try that out, it will take me a week to get the way out here, but i will let you know.

2000xjRed

Ok so try this out, in the power distro box under the hood, there are relays and fuses for the o2 sesnsors, check the 20amp yellow one, well check all of them, i had a burnt one, i cleared my p0132 code, drove it for twenty minutes and it didnt surge, hesitae, or set a code, it might be fixed time will tell i guess.
My thought is that a blown o2 sensor fuse tells the computer that the voltage was to high and blew the thing, sets the code, and if you clear the code it doesnt come on until appropriate operating temperature if there is still a problem, so if you drive somewhere real close the DTCs might not show up. try tell me what you think!

Willys55

Bad IAC can cause this. Valve may be sticking when it is closer to the stop point. P0138? This is caused when the vehicle is running to rich for too long(greater than 4 seconds @ low rpm). If the IAC is sticking closed then you have less air in the mixture and that leads to run rich condition at idle(stumble and stall).
Take the IAC off and see if it is all carboned up. There is also a way of testing the little bugger with the snap-on or otis scanner.

fafafofi

I DID have a fuse out. Changed it out but I'll have to wait to clear the code tomorrow. The lowest idle was 500 but at least it wasn't spitting at stops. I'll be pissed, but relieved, if that little fuse was the problem. I'll let ya know the outcome