RockyMountainXJ

So i just got me my first jeep a week ago, its looked clean inside an out an i got a good deal so i picked it up.
Well turns out its got some mechanical problems.
So heres the run down of what i have:
97' Jeep Cherokee Sport 4.0L manual trans.
the problem is as follows:
Sometimes i cant start it at all just by doing the normal cranking, it will crank but wont fire.
If i give it gas while cranking it will fire up but more times than not it will die immediatley if i take my foot off the pedal.
So i can start it by giving it gas and the i have to rev it an warm it up for a minute or so to let it idle by itself, but when it idles by itself it idles at about 400rpm, it'll stay running but i know that isnt a normal idle speed.
A check engine light was triggered when this all started happening i took it to autozone an ran a computer diagnostic an it came up with idle air control error.
i replace the idle control valve an it idle an ran good at 700rpm. but this didnt last to long i got it home shut it off an was workin on a few other things.
I tried to start it up again after it sat for about an hour and it went back down to the low idle.
I have replaced the battery, battery cables, and the idle air control valve.
I have fought with this thing for about a week and i cant figure out why it'll work when the new valve went in but then a few hours later its back to the low idle. the IAC was the only code that popped up on the diagnostic so im not sure where the problem could be.
Please help if you can,
Thanks.

HCCAFan

Have you checked over every line for vacuum leaks?

Cherryokee

Did you clean the throttle body and the IAC bore at the time of IAC replacement? Did you buy the IAC from A/Z (NOTE: High potential for reliability issues)? Also, search for threads on how to test the Throttle Position Sensor (TPS) and check it out accordingly. Your described intermittent throttle-idle behavior sounds like the TPS may be the real issue...

freegdr

first thing have codes been checked

RockyMountainXJ

Yes i cleaned the throttle body, and cleaned the IAC bore as much as i could(kinda hard to get in there).
Yes i did buy it from autozone, im actually runnin over there right now to have them replace it with another one and see if that helps..
and yes i will be looking into the TPS if this new IAC doesnt work.

93gc40

Whats your fuel pressure????

BuckB91XJ

X 2 on looking the engine over really good to ensure all vacuum lines are connected and tight. If that doesn't fix it. Then, check for correct fuel pressure at the test port on the manifold fuel injection rail.

RockyMountainXJ

I just called autozone so im going to replace the IAC if that doesnt fix it they also have the TPS in stock so i probably get that and try it. I'll check all my hoses to make sure they're all in good condition. an i need to get a gauge to measure exact pressure but i do know that the system is being pressurized, i held a rag over the port an pushed the stem in a little bit it squirted out so im pretty sure there is enough pressure in the system

TheJerm

Injectors need a certain psi or they wont open. I bet its the IAC

excess650

My first thought of cranking and starting with foot on the throttle was that the check valve in the fuel line or fuel pump might be defective. A leaking fuel line will aso exhibit the symptom, but leaking fuel and the associated smell are pretty obvious.

The TPS is easy to check with a paper clip and VOM. There are 3 pins and with the ignition ON (engine NOT running) one of those is ground, one supplies 5VDC and the other is the output voltage. Mine measured 5.1V input and .76-3.76VDC output depending upon throttle butterfly position. It should read lowest with the throttle at idle position and highest at WOT with a smooth, sweeping transition from idle to WOT. This is more easily seen and interpreted with an analog meter, but both of my digitals seemed to do OK if the throttle butterfly was opened slowly enough for the digital meter to react.

Check the TPS before you buy one.

customzj73

Fuel pump.

BRUNER247

Don't assume the partstore parts are good. I had a ton of problems with iac, tps, & crank sensors from partstores. Mopar parts are the only ones that would work on my xj.

RockyMountainXJ

The TPS is good! i swapped the IAC with another one from AZ.
Still runnin the same.
The CEL code is p0505(Idle air control).
Its been replaced twice an still the code is triggered i took it into the shop and had it reset an a few minutes later it popped up again.
This is frustrating does any one have any ideas besides TPS or IAC..?

jronald

Bad or broken wire to the IAC. There is a reason it keeps setting the same code.

Ron

RockyMountainXJ

alright, i'll try and trace back the wiring and check it all.
thanks Ron