cpetty

Hi All,


I have a 2000 Jeep XJ 4.0L.

On a cold start the jeep bogs down and shakes, very similar to what a carbureted engine does when you first turn it on. If I barely press the gas while moving the shaking intensifies, but if I go wide open it pushes through the shaking and hesitating. Once the jeep has warmed up it stops shaking, hesitating, and jerking all together.

At this point I have replaced:
1. Idle Air Control Module
2. Intake Manifold Air Temperature sensor
3. Spark Plugs
4. Cleaned throttle body with carb cleaner.

I've heard people say to replace the O2 sensor, but it just doesn't seem logical, because it stops after it warms up. I could be wrong though.

Any help would be greatly appreciated.

Thanks,

---88XJ---

Not sure if 2000 has timing but id check that if it does.I think the comp does it though. maybe loose plug wire or bad plug

JeepsMyName

My first hit was your tps but if it stops once your hot its probably not. I would check your fuel pressure on your fuel rail see if the pressure changes at all from cold to hot

Muaddib420

Not your O2s. They don't enter play until closed loop (warmed up). Could be your MAP sensor. I'd also check your feel pressure like the previous poster suggested.

cpetty

So would fuel pressure increase as it warms up? Thanks for the replies.

salad

Nope fuel pressure is regulated by the pump. If you attach a gauge to the test port on the rail you'll see 49 PSI.

There's an excellent writeup here somewhere by tjwalker on testing the TPS. I'd also recommend testing or replacing your coolant temp sensor, and verifying that the MAP has good vacuum.

Of course, when was the last full tune-up? Which spark plugs did you use?

cpetty

I replaced spark plug wires, distributor, and bosh plugs last night

cpetty

What temp should the 4.0 run at? I ask because it normally displayed just above 100 until on the drive home yesterday when it shot to 210

salad

Normal operating temperature is between 195 and 218 or so.

Sounds like your coolant temperature sensor is toast.

cpetty

So are you thinking that a bad temp sensor would cause hesitation when cold? If so, why? Thanks again for the help!

94JeepCherokeeMan

I would clean up my fuel rail and check for vac leaks if I were you. You should also clean the throttle body with throttle body cleaner, not carb cleaner. You could have roasted your IAC.

salad

The CTS is the PCM's primary way of telling how hot the engine it is, and how much fuel to dump in. It will can run very lean or very rich until the actual engine temp matches the faulty sensor input. You can find many other cases of the same problem on here with a search.

Your dash gauge is busted anyway. It uses the same sensor. Just replace it.

cpetty

Thanks guys I will try both tonight and let you know how it goes

cpetty

Replaced thermostat and cts last night. When I started jeep check engine came on and said no bus5. Is that normal?