jeep cherokee runs rough when starting warm?

Question

96 cherokee sport

if the engine is cold and i can start it and drive immediately, but sometimes (doesnt happen every time) if the engine is already warm and i start it, it will run very rough. its so bad that i cant drive anywhere cuz there is no power, even revving it, it sounds like a horrible multi cylinder misfire. 
its not throwing any codes, and i recently replaced the plugs, wires, cap, rotor and ignition coil, (plugs replaced just before i bought it, they look like really cheap champions, and they are gapped to spec)
all i do is let the car sit for a minute or two and it smooths out by itself and then i can drive normally. 

any ideas?

? · Accepted Answer

my guesss is yours isnt holding fuel pressure it is bleeding down so when u start it. it is getting more air than fuel causing ur back fire and missing out sounds.   but ive also heard storys of #3 cylinder gets so hot it evaporates its fuel out within that short shut down so when u start it u get rough running and misfiring till it lines out solution is heat shield.  good luck hope that helped i no u got 2 options there.... if they are right but they both cause same thing as u describe, a check valve or fuel pressure regulator can let fuel bleed off internaly back into ur gas tank basicly.

scott · Answer

a lot of people with that same vehicle complain about their vehicle running rough after a small amount of run time. There can be many different things wrong such as a bad crankhaft position sensor or you could have the distributor indexed improprly.

the main hits were for a defective upstream oxygen sensor.

1. Check for a trouble code set that indicates the upstream O2 sensor signal is shorted to voltage. 

2. Check the Cam/Crank sensor signals and sync signal. 

3. Check the signal from the upstream O2 sensor to determine if it remains too high.  

Potential Causes: Defective Powertrain Control Module (PCM)
Insufficient Sync Signal
Defective Upstream Oxygen (O2) Sensor
Wiring Harness
 
Tech Tips: The Powertrain Control Module (PCM) on this engine allows the O2 sensor signal to determine 25% of the fuel control. If the O2 sensor voltage remains too high as the PCM moves to closed loop, the controller will take away fuel. This can be seen on a scan tool, by watching the short term adaptive memory parameter.  

you are going to probably need to have a professional diagnose it for you. It is not going to be an easy diagnosis so be prepared to try and throw some parts at it some more.

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jeep cherokee runs rough when starting warm?

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