Jimbo165

Thanks for adding me to forum I have a 2000 Jeep Cherokee with 4.0 engine, auto trans I am having a idling problem that comes and goes. Sometimes no problem then at next stop engine idle goes so low engines almost stalls then just before stalling pops back up to idle then when taking off Jeep make pop with no power and then goes back to normal and off i go. I have replaced coil pak, TPS sensor cleaned IAC sensor replaced spark plugs , added dry gas and did a fuel pressure check and even when about to stall it had 48 psi pressure.Air filter ok too I have checked codes andPO443, PO132 and PO705 have come up but everyone here says that I need to fix them but they are not problems cause. Please help me find problem as this is our main vehicle to drive. Thanks Jimbo165

Radi

The P0132 might be contributing to your problem, that is an O2 sensor 'voltage too high' code. It can cause the engine to run poorly.

tjwalker

How many miles on your oxygen sensors? They have a finite lifespan of between 100k-150k in general, on the 4.0 HO engine.

Gotta chase and resolve every code. Failure to do so makes troubleshooting very difficult when the next problem comes along.

I agree with Radi and would start with new oxygen sensors. Change all of them (some of your vintage have 2, but I believe some have 4) as if one is failing, the others are not far behind. I would highly recommend using NTK for replacements as they are the OEM sensor that your Jeep came with from the factory.

Jimbo165

Well I have replaced oxygen sensor and still have problem Jeep runs great for a while and then at next stop sign idle gets rough goes down almost to zero then jumps back to normal but acts like its missing as I take off I pump pedal to keep it running then next running great. Any more ideas? Thanks

Diesel

Check and clean IAC/TPS/CPS

Cane

I had similar problems with CPS & o2 sensors.

My engine stalled because of the CPS while it did not with the o2, although the idling was bad and a putrid smell could often be smelled.

tjwalker

Have you cleared codes and determined what codes return? If so, what codes are they?

Always, always gotta let OBD codes be your guide on what your repair strategy is.

CCKen

You might want to check the fuse marked 'O2S Relays' in the PDC (see pic). It's the O2S heaters relays fuse. If the O2S doesn't come up to 600*F when operating it will give a high voltage reading.



Which O2S did you change? Does your exhaust sytem have two O2S's or four?

See pic for four O2S configuration.

brendancfarrell

Do this. I dove in head first and changed an o2 sensor, alternator and yellow top and it ended put being a simple fuse. Let us know if that changed anything.

Jimbo165

I checked the O2s fuse it is okay I donot believe O2 sensor would cause problem I have. I checked codes again and they do not show a misfire on them. Could fuel injectors act up at a idle but be ok driving down road? Another thing I donot understand is Cherokee idle start messing up then goes almost to zero then something causes it all of a sudden to go to a higher idle then it settles back to normal but if I take off engine has no power and acts like it is missing I pump pedal by habit then next thing off we go and all is well till next extended stop. It is a real hair puller I have not alot of money to just buy parts that do not get it going. I am down to fuel injectors, crank ps, cam ps, computer and all 02 sensors just do not know which to try next. Thanks Guys Jimbo165

Radi

Next thing I'd do is clean and inspect the Idle Air Control Valve (IAC). That's what regulates idle speed by allowing air to bypass around the throttle butterfly.
Sounds like yours could be sticking.

ThunderThighs

I would try taking off the terminal clamps and cleaning those up really well. And even take a look at the cables.. If you haven't already.

I had somewhat of the same issue when I started mine up it wouldn't hold an idle. The terminals and clamps had a bunch of corrosion, cleaned them an problem went away.

When mine get like that it causes all sorts of fun problems to deal with.

brendancfarrell

Hmmm. I could say check your injectors. I'm assuming they are stock? One may be clogged, but you said no misfire codes were popping. It's not had to check them. Could also check your fuel pressure. Rent a gauge and see what it's at. I don't know the number off hand

CCKen

If you can, get a scanner that can give you live readout of the O2S activity including whether the system goes into Closed Loop or stays in Open Loop, and the Short Term Fuel Trim activity.

I had a similar (intemittant) problem with my '99 but not as severe as yours. At idle, my RPM would droop to almost stalling then recover to normal idle RPM. I never attempted to drive away right after recovery so I don't know if it would 'pop' when accelerating.

I hooked up my scanner and saw that when the RPM droop occurred I was in Closed Loop. It showed that my upstream O2S was pegged at .90 volts (900 Millivolts) and the STFT was maxed out at -36%. This meant my upstream O2S was seeing a very rich condition (very little Oxygen in the exhaust stream). During the recovery the STFT stayed at -36% until the upstream O2S went to .02 volts (max lean). The PCM was pulling fuel off big time until the O2S saw a very lean condition (high oxygen content in the exhaust stream). After full recovery the STFT settled in at 0.00 volts then returned to normal readings and the O2S was cycling rich/lean normally, albeit, on the rich side (STFT negative (-) numbers).

My problem hasn't returned after installing a rebuilt engine. I don't know what I did to fix it but during the install of my rebuilt engine I did make these changes:

New exhaust manifold (old was cracked)

Different fuel injectors. The old ones were 0280155789's which ran a little too rich. Installed some Ford XFE-C4B injectors, which run very good. STFT nearly perfect.

New ECT Sensor, as precautionary measure because of its age.

Cleaned IAT Sensor bulb with MAF cleaner. It was oil soaked.

New OEM TPS. Old one was a POS BWD TPS that always gave a high voltage reading at idle setting.

New Plugs, wires, cap and rotor.

Things that remained the same:

Same distrubutor with the same OEM Camshaft Position Sensor.

Same OEM Crankshaft Position Sensor.

Same ignition coil.

Same OEM Map Sensor.

Same IAC.

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Data I got off the net concerning negative STFT numbers:

* When the [STFT] numbers are negative, the computer is subtracting fuel to compensate for a rich mixture. The most likely reason is a dripping injector. This will drive the other cylinders extremely lean, almost to the border-line of misfiring. The result is that on quick acceleration from a dead stop, the engine may hesitate, stumble and stall.
A leaky injector will be less detrimental at higher speed (2000), since the number of drips is only 30% of what it would be at idle. To prove this, increase speed to 2000 RPM and observe the short term percentage number dropping toward zero.

** Diagnosing with Fuel Trims
Fuel trims can help you zero in on the problem, especially when there are no other trouble codes present. Knowing whether a vehicle is running too rich or too lean will help narrow down your diagnosis. Fuel trims that differ greatly from one cylinder bank to the other will also point you in the right direction. Always evaluate fuel trims at idle and at 2500 RPM.
Running too rich – High negative fuel trim corrections can be caused by MAF sensor problems, high fuel pressure, leaking fuel pressure regulator diaphragm, faulty evaporative emissions components, leaking injectors, defective O2 sensors, exhaust leaks/pinholes before the O2 sensor, coolant temp sensor problems, and base engine issues such as low compression and incorrect camshaft timing.

~~~~~~~~~~~~~~~~~~~~~~~~~

Based on the above data you may be experiencing a rich condition that the PCM is compensting for by pulling fuel off to the point that the engine is running very lean [see blue text above] causing the RPM droop and the 'pop' when you accelerate.

Something is dumping fuel in your engine. See last paragraph above.

The MAP Sensor is the number one contributor to rich/lean running conditions. The Cam Sensor determines fuel injector timing and pulse width. The ECT Sensor can cause a rich condition if it provides the PCM with a cold condition voltage [this should show on your temp gauge as well]. IAT Sensor, same thing.

I think I would be looking into a dripping [leaking] fuel injector(s) in this case.

jamurrin

You checked codes...and do not have misfires...but do you have some other codes??? They might hold the clues you need!