Subsammich

Hey there everyone, I have been browsing this forum for some time now, but haven't had the need to make an account, well today is the day. I'm a touch stumped and could use some help from the gurus!

The basics:

1998 Cherokee Sport 4.0 I6 ~172k on it. [New purchase for me]

Check Engine light was on when I bought it, guy said he thought it needed a new IAC valve. Idle is a little jumping but nothing more than a few hundred rpms. From what I found searching people were going from 1200 to 300 and this isn't my issue at all.

The issue that worried me the most is from 55-70 it is slipping, jumping, whichever adjective works best for you. It's intermittent, and my original thought leaned toward trans issues. So this past weekend, I did some maintenance to it, which included dropping the trans pan, changing fluid, cleaning pan, replacing gasket. To my surprise there was NOTHING on the magnets.

After this I removed the throttle body, and iac valve from that to clean them up and they were both fairly clean, but still got them as shiny as I could. Changed the oil and filter and called it a day.

Now the check engine light went away, drove it a few hundred miles back home and around a little with not one slip, no start issues, no check engine light. It WAS running like a top!

Now this morning, its a little colder, and I hopped in to start it with no luck at all. Cranking good, just wouldn't fire up. so After a few tries, I decided to pop the hood, remove the plug from the IAC and plug it back in, viola started up. While driving to work, it was slipping again all the way their intermittently on the highway. Which makes me lean towards it might not be the trans slipping, but something in the engine?

I had them run the codes @ autozone before the maintenance, and it leaned toward the CPS, which I plan on metering out today to see if all is well there.

Hopefully I explained my situation well enough, I'm a little curious as to what we did that made the check engine light go away during that maintenance, and I'm unsure what happened to make it come back after 250 miles of running so well.

cruiser54

CPS is so common of a failure that I'd just replace it.

Subsammich

I plan on it. I'm leaning towards a throttle position sensor now that a friend told me about it and have started some research.

Subsammich

Changed tps and issue is still here.

Had them pull cel code again and got P0340. Why would this cause my engine to jerk while @ highway speeds. Yesterday it almost made my car stall @62 mph. I was leaning towards TPs causing this, and have yet to diagnose with a meter, but not sure how to recreate the situation while testing other than looking for dead spots.

cruiser54

How are the plugs, wires, cap and rotor?

Subsammich

I'll have to give them a twice over tomorrow.

As of now I replaced the CpS (on the side of the highway actually) and all symptoms went away. No CEL, no studder on highway, fired right up after being stranded on a stall/no start on the side of the highway.

Seems to be resolved.

SteveMongr

I have learned to take the advise and suggestions of Cruiser54 first.
Guess you have learned the same. lol
Glad you fixed it!

Subsammich

Thanks I did replace with an OEM so hopefully it stays that way!

Subsammich

Well, the problem is back again!

After changing the CPS it ran great for ~ 100 miles and CEL is back on after a rough start.

Still lurching on highway as well.
Going to do some more wire checks to ensure condition of wires and probably will swap out the cam position sensor.

Going to take a good look at the distributor while I'm swapping the cam position sensor. Not sure when the plugs cap and rotor were, or if, they were ever replaced. So might add that to the cart and throw a bird and kill two stones.

Subsammich

Changed the cam position sensor (ignitor stator, pick-up coil, whatever you call it) and bought a new rotor and cap but after inspection of OEM they seemed to be fine, so just keeping them around for now.


No change in status, cleared code and on first turn of the key code (P0340) comes back, tried this 3 additional times.

Printed out all the schematics for the wiring today and will be trying to diagnose further with wiring and splice points.

Did unplug the amps fuse for the 2 10" subs in the back, wondering if power draw during startup could be an issue for signal loss.

I'll report back, even though it's just me talking to myself. Maybe eventually someone will stumble on this thread with the same issue.

Happy holidays!

cruiser54

R*C*B*R*C

Refresh Connections Before Replacing Components.

Subsammich

Connects have been, other than @ the pcm.

Subsammich

So I took some more time today and cleaned up the dip stick ground better than i did the first time, still with no luck. I decided on a limb to try changing the cap and rotor that I previously purchased. I swapped these one at a time to try to test a single variable. The cap was first and it took the CEL away, but it then came back in idle. Rotor seemed to have no effect really.

Question, the small cylinder on the left side almost on the firewall, with two lines that run to it with a pressure relief looking cap, what is that? The module the two hoses hook to has a ticking noise coming from it @ idle.

Subsammich

to my previous question, it looks like something to do with the ac unit.

i thought my engine had a tick before i put my hand on the electrical connection and felt it click there.



Swapped out plugs and wires today for Bosch wires and Champ Copper Plugs, haven't ran it yet, but not feeling confident it had anything to do with the issues I'm having.

I used a meter a poked around the pcm and camshaft position sensor and all seems fine, can't seem to find a short or anything, cleaned up a couple grounds that i could find and still seeming to have some hesitation when starting and i would imagine the chugging/jerking/jumping is still going to occur while driving.

Could i have an issue with the MAP sensor or PCM itself?

Subsammich

Jeep seems to be running well with no CEL. I'm going to ohm out wires I replaced just to see what results I get. Few of the replaced plugs had larger then ideal gaps so that could be a source of issues aswell.

Lots of qwerky issues to still chase down on it still, but as of now the big one is solved.