'96 Cherokee Sport Stumbles

[Lucihale]

Hey guys, long time no posts-
So my brother got himself a Jeep. Got a few minor problems, but all in all, good shape. I need help diagnosing one in particular.

Changes-
The fan and temp gauge stopped working and the previous owner installed an aftermarket gauge, and a elec. fan that has a manual switch on the dash. The air filter has been changed to a cone filter that rests inside the old intake box. The muffler is a (stupid and annoying) performance muffler off of like a civic. I don't THINK these have anything to do with it, but I gotta mention it because it's not stock and it may help you guys.

Symptoms-
At 1900-2000 rpms (approx.) regardless of if it's cruising, or accelerating the engine "hiccups"(?) SOMETIMES. Meaning, there is a drop to no power, and then works again. (Thinking air bubble in fuel line) It also has a semi-irregular idle.
I just changed the fuel filter yesterday, which poured out the most rust colored gas I've seen. It drove fine for the test-drive I took it out on, but I'm told today it was back to stumbling,(?) and started idling at about 2000rpms. (after the filter change yesterday it sat happily at 1100.)
The Jeep sat in some guy's yard for the summer with only a little bit of gas in the tank and on the day my brother drove it home the idle was irregular and it would stall at stoplights if it dropped in rpms. The stalling seemed to work itself out over the 50 mile drive home, but the stumbling remained.
The power seems more than ample at all other times.

I'm not that familiar with these Jeeps and I'm gonna pop into the specs on this forum to check all of "features" that could have gone wrong between the fuel tank and the engine. I like working on my '73 CJ5... It's SO much less complicated.


THANK YOU ALL for your help in advance,
you guys have helped me a few times now.

 

[blown XJ]

what motor and year? that could help narrow down possible problems

 

[Lucihale]

It's a 1996, with a 4.0. Please feel free to ask whatever questions you need, I'll try and get a quick response from my brother.:shades:

 

[blown XJ]

i would try a good complete tune up. my 89 had the same prodlems did a full tune up and ran much better.. i also left the battery unhooked the whole time i tuned it up so the computer would reboot. fix my rough idle and hiccups

 

[Lucihale]

I'll give it a go! Thanks again, and I'll report back if it cures it.

 

[MudderChuck]

A sticky IAC can cause high or low idle that sometimes changes (pretty common). The fix can be as simple as squirting some spray oil into the IAC opening, then repeating a few times after the motor has run and sucked some idle air through the IAC.
The temperature sender in the thermostat housing controls the aux fan, along with the A/C controls. The same temperature sender, helps the PCM adjust (optimize) fuel to air ratio to the motor temperature (along with input from other sensors).
In my 96 I can check the MIL codes (engine trouble codes) by turning the key on and off three times and counting the number of pulses at the engine trouble lamp. It often takes a little practice and a few tries. The process hs been covered on many posts and the code list is available. I've heard some 96's will provide MIL codes, some won't, mine does.
Got to wonder how the fan is wired, the PCM usually turns on the fan from input from the motor temperature sensor in the thermostat housing or a signal from the A/C if it is turned on. Adding switches or power into the PCM circuits may cause grief. There are inexpensive kits and various write ups on how to do this safely in OBD 1 and II vehicles.
Anytime I get that 2000 RPM buck, I tend to check the O2 senors and/or the wiring to the rear or number two O2 sensor. It may run without the rear O2 sensor, but it is unlikely to run well. The wiring for the rear O2 sensor is vulnerable and is often damaged or cooking on the exhaust. O2 MIL codes can be intermitant and may not show up on a MIL code test, but may momentarily illuminate the check engine light under certain driving conditions.
Anytime a vehicle of mine has been sitting for awhile, I run a couple of doses of injector cleaner in the first couple of tanks of fuel. Besides the rust (from water separating from the fuel and settling in the bottom of the tank), the varnish and jelly from old fuel can cause all sorts of grief. Injector cleaner and/or gas tank antoifreeze will usually suck the water/moisture back into suspension and keep it from freezing into ice chunks or causing ignition problems at the plugs. There is usually some moisture in all fuel, it usually only causes grief when it is becomes too much or falls out of the fuel, seperates and settles to the bottom of the tank.
Excuse my typo's, coffee and keyboards don't mix, maybe I should put my keyboard int he dishwasher LOL.

 

[SteelHeadz]

I didn't see the TPS mentioned to be a possible culprit. If the TPS is intermittently open during acceleration , it can cause a stumble. Check that as well and make sure there's no flat spots.

 

[blown XJ]

ah i knew there was something else i forgot about the tps. i had to change 3 of them since i have owned my xj. there isnt much room between the firewall and the header tubes i kepted cooking the wires.. chaulked it up to a jeep learning curve

 

[Lucihale]

AH! Gentlemen I can't thank you enough for the detailed input! It had a hard time starting this morning (which leads me to believe I need to clean the IAC), so we drove to Advanced to pull some codes. Came back as a bad TPS, which only seems to run about $40. HOWEVER, now I'm gonna check those wires as well to make sure they're not toast. I'll shout back when I get a chance to actually get in there and poke around. It's snowing like a ******* right now... Which my CJ5 is loving. heh.

 

[Lucihale]

Hey! Caught a break in the clouds... Wires look fine and a bad sensor wouldn't really surprise me anyhow. The throttle body was CAKED with crap, as was the IAC. It took some real good spray and wipe action, but I almost HEARD it click and start working once I turned her over and ramped it up a few times. Now with a quick drop in throttle down to the idle, it runs just fine. Would've stalled 30 min. ago. So it looks like I'm 1/2 way there, a new sensor in a few days and I'll report back. Thanks again!

 

[Lucihale]

Just to be conclusive, so that others might be able to use this; I replaced the TPS, and cleaned the IAC. Cleaning the IAC stopped the stalling problem when coming to a stop, and the irregular idle. The TPS is only a couple of days old, but everything seems to be running far better, with no stumble. Total cost of repair- 39.00 TPS, and 3.00 can of cleaner, which I had already.