[garman18]

I have a 1999 Jeep Cherokee that has been having an acceleration issue for the past 2 months. The Jeep will start and idle fine. When you go to pull out it will hesitate, like it is losing power. It will then kick in and run fine. Sometimes it will make a popping noise. I have replaced the following items and the problem still exists. The throttle position sensor, crank sensor, maf sensor, IAC, both 0-2 sensors, coil, distributor, rotor, pick-up, wires and plugs. The only DTC's I get are related to the 0-2 sensors with the upstream sesnor showing a malfunction and the downstream showing high voltage. As stated both have been replaced and the hesitation still exists. Once out on the road the vehicle runs fine and shows no signs of problems. I have cleaned all of the electrical connections, due to finding black sludge on the PCM connections. The problem still exists. Could the PCM be causing this and is there any way to check it?

[budman1]

This is the exact same problem I am having. The only thing I have not replaced is the IAC motor which I just bought and paid 105 for. I have a friend at a Jeep dealer and he is looking around for a PCM for me to try as that might be the problem. Good luck and let me know if you find anything.

[garman18]

I found a computer place on Ebay that sells rebuilt PCM's and he is sending me one. I hope to get it installed within the next day or so. I will let you know how it works out.

[budman1]

to the top!. Alot of people are having this problem and so far nobody has figured it out yet from what I have read. I'm going to throw a coolant temp sensor at it today and see if that helps. I know this will not help with the o2 codes it throws but I really hate the hesitation problem. I cannot get my inspection sticker until I figure this out which I am running out of time

[garman18]

Let me know if the coolant sensor helps. My computer is on its way here and if I notice any changes I will let you know.

[budman1]

I decided to hold off on the temp sensor as my buddy told me that its probably not it. As a 25 year chrysler mechanic I will listen. I have yet to get a pcm, hoping he finds one today.

[Morris4x4Center]

In my 1997 4.0, it was the temperature sensor, sort-of. It was actually a bad connection at it. I guess over the years the elements got into it and the connection went bad. It would start and run great, until it warmed up. Then it would bog off the line but be OK once it got going. Cleaned it with electric contact cleaner a brush and a piece of copper wire, haven't had the problem since!!!

[budman1]

Try unplugging both O2 sensors and see if it goes away? I did tonight and it ran with no hesitation or studder. My front sensor is brand new from chrysler. I will try in the morning with just the rear unplugged and see if it does it.

[dobedyje]

My '99 has the same exact issues (90k miles). I've replaced the distributor, plugs, rotor, wires, water temp sensor & the fuel pump -- no help.

The fuel pump is a common issue, but not cheap. I replaced the whole assembly including the pressure regulator since my engine would pulsate as if the pressure was increasing then decreasing.

I've seen some comments about the Automatic Shut Down Relay (ASD) that make me interested. I've tested the Fuel Pump Relay but not he ASD.

[dobedyje]

Last evening cleaned ground connection from engine block to firewall, removed coil & cleaned all connections, tested the ASD & Fuel pump relay (both check put according to my manual which makes sense since the issue is only obvious for 1-2 minutes after start-up). --- No help.

I pulled the fuse for the O2 sensor at lunch today, this made it worse & lost a lot of power.

[mickc9129]

I stopped one time to help a lady who was sitting in her car along side the freeway with engine idiling. Said the car would not go past 40 mph and that it was a rental car. I pulled the top off the air cleaner and it looked like the inside of a full vacuum cleaner bag. Took that bugger out and cleaned the inside and she was off to the races.

[garman18]

I replaced my computer with a rebuilt one and it looked like the problem was solved. However when I used the Jeep again last night, the stutter and popping noise was back. I am going to scan the computer today to see if there any pending codes, hopefully this computer will give me something different then the o-2 sensors, which as stated before have already been replaced. My Jeep does this when its cold, so I don;t think the temp sensor will help. I have a Rock-It cold air intake, which I clean regularly, so I clean it again to see if that helps. I am thinking about dropping the fuel tank and looking at the strainers. I have 48 psi on the fuel rail, but I don;t know what else to look at.

[dobedyje]

I finally gave in and changed the front 02 sensor & it fixed my problem,at least I haven't had any problems the past two days.

Garman18, have you checked the fuses for the 02 sensors, there is one in the Power Distribution Center under the hood, check out slot #24. Also slot #21 in the fuse panel by the passenger kick panel.

[Jeepokee]

Front O2 sensor fixed it for me as well.

[garman18]

I replaced the front o-2 sensor for the third time and this one seems to be working. I bought the other two through the dealership and this one I got at Advance Auto Parts. So far its been running great. I still can't believe the both of the other 2 new sensors were bad. I am going to check the fuses just to make sure there is nothing else going on.