1999 Jeep Grand Cherokee loredo WJ 4WD 4.0L
At idle, the engine has a constant roughness to it. This can be felt inside the car. The tailpipe gives out an intermittent puff while idling (also felt inside the car as a hard miss feeling). I can hear exhaust leak(s) while idling. No codes, no erratic tachometer. Tach. barely moves, if at all, while the roughness is present. While driving, everything seems smooth.
Engine was rebuilt about 3000 miles ago. Same symptoms were there with old engine. Roughness was present from the time the car returned from the engine install.
Another issue that was present with both engines, may or may not be related, at a cold start and idling, it sounds like clattering coming from under the car. Its louder and sounds like shaking marbles in you hand. Within about 1-2 minutes, it fades away to quiet. Returns after about 2 hours sitting turned off. Local mechanics ALL guess that it's lower engine noise. Everything is new in there..LOL
The re-builder runs the machine shop at my work. He is a Mopar guy that has done hundreds of the 4.0's! He assures me that there isn't a problem with the engine. As I said, the chattering was there with BOTH engines!
Things I have done:
Engine, mounts and spark plugs (Champion copper)
Oil pressure and Coolant temp. sensors (not Mopar)
Removed throttle body and sensors. Cleaned throttle body and IAC orifice. Installed Mopar (All three) sensors and new TB gasket.
Replaced ALL injectors with new Bosch 4 hole injectors.
Smoked the intake system through the brake booster vacuum. No leakage seen!
One thing that does concern me. When I purchased the IAC from EBay, the Mopar part number I found for my year was not available any where. The Seller claimed that the Mopar sensor he sold me would work. The Mopar number he sold me was 4874373AB. EBay fitment said it would work but the Mopar parts sites said it wouldn't fit. But they didn't list my year anyway.
Sorry for the length of this post. I wanted to get as much as I could in it.
At idle, the engine has a constant roughness to it. This can be felt inside the car. The tailpipe gives out an intermittent puff while idling (also felt inside the car as a hard miss feeling). I can hear exhaust leak(s) while idling. No codes, no erratic tachometer. Tach. barely moves, if at all, while the roughness is present. While driving, everything seems smooth.
Engine was rebuilt about 3000 miles ago. Same symptoms were there with old engine. Roughness was present from the time the car returned from the engine install.
Another issue that was present with both engines, may or may not be related, at a cold start and idling, it sounds like clattering coming from under the car. Its louder and sounds like shaking marbles in you hand. Within about 1-2 minutes, it fades away to quiet. Returns after about 2 hours sitting turned off. Local mechanics ALL guess that it's lower engine noise. Everything is new in there..LOL
The re-builder runs the machine shop at my work. He is a Mopar guy that has done hundreds of the 4.0's! He assures me that there isn't a problem with the engine. As I said, the chattering was there with BOTH engines!
Things I have done:
Engine, mounts and spark plugs (Champion copper)
Oil pressure and Coolant temp. sensors (not Mopar)
Removed throttle body and sensors. Cleaned throttle body and IAC orifice. Installed Mopar (All three) sensors and new TB gasket.
Replaced ALL injectors with new Bosch 4 hole injectors.
Smoked the intake system through the brake booster vacuum. No leakage seen!
One thing that does concern me. When I purchased the IAC from EBay, the Mopar part number I found for my year was not available any where. The Seller claimed that the Mopar sensor he sold me would work. The Mopar number he sold me was 4874373AB. EBay fitment said it would work but the Mopar parts sites said it wouldn't fit. But they didn't list my year anyway.
Sorry for the length of this post. I wanted to get as much as I could in it.
Aug 25, 2026 at 5:56 PM
