Fatcherokee

So I got my first jeep a few days ago, it's a 99 cherokee sport. The guy that had it before me said it ran a little rough at times and he disconnected the iac and loosened the screws to allow air in to keep it from stalling. It would run rough and occasionally stall at idle and sometimes surge while going highway speed.
Now, I have since then cleaned the throttle body, including the iac and all the ports, plugged the iac back in and tightened it down, replaced the tps, plugs, wires, cap, and rotor. I have verified it is getting spark, and turning the key gets about 48 psi to the fuel rail. It has a very hard time starting now and if I can manage to get it running I have to hold it at about 1800 rpm to keep it running. I really don't want to take it to a shop but I'm running out of answers. Also, the previous owner said the upstream o2 sensor was replaced recently. Thanks in advance.

94XJYKuz

Hello Fatcherokee,
Welcome to the forum. Sorry about your trouble. Your engine needs 4 things to run properly. Fuel, Spark, Timing, and Compression. You obviously have trouble with one of the four. I would encourage you to start with a compression test. It's easy on the inline six and takes very little time. It will tell you is the problem in the engine or outside the engine block. You are getting spark and fuel so we have already downgraded two possibilities to not likely. Were it me doing the diagnosis I would throw a timing lite on it for a quick check of the timing then proceed with a compression test. Thanks, and good luck. My guess' are either the timing is way off or an internal engine issue. Do you have any codes?

dac612

Sounds like the IAC could just be failing. If you induce a vac. leak does it help at all in start-up and idle quality?

from what I can tell the p/o was on to something and you may need to replace teh iac. I recommend going to mopar for it but hey a parts store run may be faster and they've worked for me.

The tps. even though it is new. It's still worth checking the readings it gives you since parts like that can come wonky right from the start. And it's just good to be able to remove that as a possibility since that is another common cuplrit to your symptoms.

The other item worth checking/replacing is the crankshaft position sensor. From Mopar only preferably. That guy will go bad eventually and will cause all kinds of headaches. If a new iac doesn't fix your issue, I'd return it and buy a ckps. Both the iac and ckps are kind of hard to diagnose but they both especially the ckps are worth replacing as they will go bad anyway.

Fatcherokee

Hooked my scanner up (CEL isnt on) and i got codes P0122 and p0705. I get the p0122 with the old and the new tps. I will have to get a compression tester and try that next. It has 250k on the clock and I'm not sure if the motor has ever been touched.
As for inducing a vacuum leak, it didn't seem to change much when pulling off various vacuum hoses. I plugged them all to see if there could be a leak anywhere also. No change. I will test the old and new tps here shortly and try to find a new iac. Thanks for the help

Fatcherokee

Alright, just tested the old and new tps. With an input voltage of 5.18, the old one gave me .79 at idle and 4.06 at WOT. The new one gave me .89 at idle and 4.12 WOT. Are these numbers okay? From what I read it should be .5-5 volts. Also, with the iac removed should the plunger on the end move somewhat freely or no? I pulled it out and pushed the plunger in all the way and plugged it back in and attempted to start it and it stayed all the way in

Fatcherokee

Just finished the compression test. Cylinder 5 has no compression. The rest are all close to 150.