Ok. I'm not completely new here (old comp had old account), so I made sure to search this problem as much as possible. I have a feeling I'll get pointed in the same direction as the many other posts I've read, but there was one thing that popped up in those that made me want to post and ask.

Anyway...

1996 Cherokee Sport
4.0, auto.

For quite a while, it's been getting harder to start. Wouldn't take anything but a few extra cranks to get it started. Every once in a while, I would go to start it, and it would just kind of stumble to life and never pick up the idle. When that would happpen, I would just shut it off and start it again, and it would be fine.

If the Jeep had sat for a time (like overnight) I would start it (with the extra cranking) and it would start fine, and then seem like it was ok until I backed out of the driveway. When I would go to drive forward, it would bog down, hesitate and run really rough.

I'd keep my foot in it through the stumble, and then I'd hear a muffled pop (sounds more like a *pup*) from under then hood, and as if it had cleared it's throat, and then it would drive fine, often without a problem until it sat again overnight.

But then the other day I went to start it, and it would just crank. I tried to start it by giving it a little throttle, and it started right up, but it would die if I let off the throttle. I could hold the throttle and get the engine to run in the 1500-2500 range, and could get it to rev up with a little coaxing, but throttle control was way off. Felt like I almost had to pump the throttle to get it to rev past 2500.

When I'm doing that, and when it's fighting me for RPM I hear that same *pup* pop. I'm going through the cap, rotor and plugs now to see how they look, but after that, I need some direction.

Obviously the TPS, CPS, and all the other usual suspects are there, but I just wanted to see if anyone had seen something a little more like what I'm dealing with.

Thanks for any assist.

~SoCo

 

You're on the right track, that thump/pop you're hearing is probably late detonation or backfire. This also sounds like an issue my friend had with his XJ; he had a stuck lifter that wasn't letting either the exhaust out or air in, can't remember. Might try running something through the crank case to break up sludge that may be making the lifter stick and then putting in some new oil.

 

Ok, so here's an update.

I went out to mess around with the Jeep, and I started it up (with the throttle) and was feeling out the throttle. As the engine started coming up to temp, the engine started running better and better. By the time the engine had come up to operating temp, if felt almost completely normal, except that it would still not hold an idle.

I could get it to idle speed, but if I let off the throttle, it would still die.

So I jumped out and unplugged the IAC just for the hell of it. So I started it up (with a little throttle) and then let off the throttle, and it actually settled down into a normal idle. I shut it off, and then started it right back up (no throttle) and again it went into a nice idle.

So then I plugged the IAC back in, and it still started right up and went to idle. I figure that's because it was already at temp and wherever the IAC is stuck it's ok there. I suppose then that the IAC motor is bad, the connectors are all clean and in good shape, and the IACs ports show no excessive buildup (in fact almost clean enough to not get a finger dirty).

I still get a little stumble when I come to a stop, and the motor feels a little hesitant and restrained when I floor it. But I haven't fixed the IAC yet, and it needs a tune up really, really badly. I'll see how that all pans out after a good tune up on it.

 

Had similar problem with my 92 4.0. Changed out crank sensor, pickup coil, new coil & wire, taped bare wire behind distributor & new coil pickup. Its running better than it has for 2-3 years. Going to replace IAC tomorrow just because of the other stuff has never been changed out until now. Cheap car payment for a regular driver @ 143,300 mi.. I was on here last week with the problems and this has been the solution for me...Thanks CF glad your here, Rex.