I have a '98 Jeep Grand Cherokee that hesitates during acceleration. This problem usually occurs when I first start the vehicle. When this occurs, if I stop the vehicle, it idles funny. It will rev then sounds like it will stall repeatedly until it smoothes out. After it smooths out, it runs fine and with no problems. I have pulled the fuel pump and cleaned the filter that is attached to the fuel pump, I have changed all plugs and wires, and replaced cap and rotor. I also looked for an EGR valve but was unable to find one on this vehicle. When it does bog out, if I give it gas, it leads to (what I believe) is a spark knock. My next step is to check the throttle body. By the way, this vehicle is a strait 6. Any other ideas would be a huge help. Thanks...

Are you getting any codes from the computer? How many miles are on it?

(you can get codes by turning ignition on-off-on-off-on within 5 seconds - without starting - then you'll get the codes flashing on your odometer.)

Check them out and let us know what you find.

Well, I looked for the codes and nothing came up... The vehicle has 84,000 miles on it and runs very good except for the hesitation. (The hesitation only comes up about twice a day, and always after I start it.) It's as if it is not getting the fuel it needs. When I pulled the fuel pump, and disconnected the fuel line, it had plenty of pressure in the line which throws me away from the idea of the fuel pump going out. Any other ideas are greatly appreciated... Thanks...

I'm thinking that since it's only right after startup, when the engine hasn't warmed fully (based on your description) that you could have some carbon build up in the intake that's not letting the sensors adjust to the cold condition. I've seen other posts on the 4.0 liter that a good cleaning of the intake solved rough running or idle issues.

Thanks for the info. I will give it a try and let you know... I'm really reaching for any answer and am willing to try anything. If you think of anything else, please don't hesitate to let me know... Thanks.

I found this post and it sounds like this guy is having the same problem that I am. This description sounds like my jeep to a "T"... I need help...


"I have a problem with my 96 cherokee (130k, 4.0 I6) that seems to stump a lot of gearheads that I know, I'll tell you as many details as needed, hopefully someone has had a similar experience and can help:

When accelerating to cruising speed, ONLY the first time after startup, the engine suddenly bogs in rpm and loses power somewhere between 15-35 mph (sorry, no tach). This power lost can last anywhere from 1 second to 4 or 5 seconds, and only seems to get worse if I press on the gas more. When it does pick back up, it REALLY picks up and I can feel a very noticeable difference in power. As I mentioned, it only does it within seconds of starting the vehicle, and accelerating the first time after startup. When I do accelerate, it make a popping noise from the engine or mabye the air cleaner.

It is fairly sparatic on doing this, not every time, sometimes it can go days without doing it, then sometimes 3 times in a row one day (upon consecutive starts).

Seems to do it whether engine is hot or cold.

Air filter is good.

Fuel filter replaced about 20k ago.

Seems to be independent of fuel level in tank.

Tranny fluid level and color is good, flushed about 30k ago.

New TPS sensor about 35k ago

Any help would be great.:banghead:"

I have exactly the same problem as described in the previous post. Since last posting, I have replaced the TPS, MAP sensor, and IAC valve. I have also pulled the injectors and cleaned the intake and injectors. I have been told to change the fuel filter but it does not make sense to since it only happens once after I start the car. If it was the filter, I would think that it would be a continuous problem instead of a one time thing after starting. Mabye another kind of sensor? I need help, it's driving me crazy. It can be very dangerous when getting on the freeway right after starting the car. I do this sometimes and it just decelerates on me. :banghead: :shakehead :disappoin

I found this post and it sounds like this guy is having the same problem that I am. This description sounds like my jeep to a "T"... I need help...


"I have a problem with my 96 cherokee (130k, 4.0 I6) that seems to stump a lot of gearheads that I know, I'll tell you as many details as needed, hopefully someone has had a similar experience and can help:

When accelerating to cruising speed, ONLY the first time after startup, the engine suddenly bogs in rpm and loses power somewhere between 15-35 mph (sorry, no tach). This power lost can last anywhere from 1 second to 4 or 5 seconds, and only seems to get worse if I press on the gas more. When it does pick back up, it REALLY picks up and I can feel a very noticeable difference in power. As I mentioned, it only does it within seconds of starting the vehicle, and accelerating the first time after startup. When I do accelerate, it make a popping noise from the engine or mabye the air cleaner.

It is fairly sparatic on doing this, not every time, sometimes it can go days without doing it, then sometimes 3 times in a row one day (upon consecutive starts).

Seems to do it whether engine is hot or cold.

Air filter is good.

Fuel filter replaced about 20k ago.

Seems to be independent of fuel level in tank.

Tranny fluid level and color is good, flushed about 30k ago.

New TPS sensor about 35k ago

Any help would be great.:banghead:"

I have exactly the same problem as described in the previous post. Since last posting, I have replaced the TPS, MAP sensor, and IAC valve. I have also pulled the injectors and cleaned the intake and injectors. I have been told to change the fuel filter but it does not make sense to since it only happens once after I start the car. If it was the filter, I would think that it would be a continuous problem instead of a one time thing after starting. Mabye another kind of sensor? I need help, it's driving me crazy. It can be very dangerous when getting on the freeway right after starting the car. I do this sometimes and it just decelerates on me. :banghead: :shakehead :disappoin
I Have a 98 jgc and I am having the same problem I cant figure out what is happening I just recently changed the catatlyc Converter and the O2 sensors it improved a little but still hesitating. No codes on the computer Need some Help!

I Have a 98 jgc and I am having the same problem I cant figure out what is happening I just recently changed the catatlyc Converter and the O2 sensors it improved a little but still hesitating. No codes on the computer Need some Help!

had the same problem with my 98 grand cherokee and there was carbon build up. i drizzled SeaFoam down the throttle body and when the engine began to choke i revved it up and tons of grey smoke blew out the back, which is Carbon. after it cleared up it ran great and i got great gas mileage too. but you have to be careful and DRIZZLE SLOWLY down the throttle body until it starts to choke then stop drizzling and rev the engine right there under the hood till it clears up.

what do you mean by seafoam?

The only way to properly check the fuel pressure is with a gauge.
On a '98 the ignition on-off-on-off-on method to check for codes does not work, you need to check for codes with a scan tool.
Seafoam is a commercial decarbonizer, water displacement, fuel stabilizer product you can also add to the fuel tank.