Jeep Cherokee Rough Idle/Heat Soak Fix

In this video, I show how I fixed the rough idle in my 2000 Jeep Cherokee Sport.

The rough idle is caused by a combination of the outside temperature being high and the engine temperature being high as well. When the vehicle is turned off in this condition, there is no fan running or any way to direct the heat out of the engine bay. Subsequently, this trapped heat “soaks” into the injectors causing the fuel inside to vaporize and become gaseous rather than liquid. This is known as “heat soak” and “vape lock.” The vaporized fuel cannot be injected into the cylinder causing the engine to then misfire and become out of balance, causing the rough idle and shaking of the vehicle.

To fix this problem, the injectors have to be insulated from the ambient heat to keep from vaporizing the fuel. Mopar makes an insulator that does the job. You will cut the insulation to fit around the injectors and then zip tie in place. I would also recommend using heat tape over top of the insulation just for added protection.

Link to insulation: https://www.amazon.com/MOPAR-56028371...

The TSB is located here: http://www.wjjeeps.com/tsb/tsb_wj_180...

It seems to be only a problem on the high output 4.0 engines from Chrysler. I went to a dealership and I literally watched the guy pull up the same TSB as listed above (I had it pulled up on my phone to verify) then close the window and tell me it was proprietary information and I needed to pay $120 to talk to a mechanic. He also said that my ECM had to be replaced and reflashed which was a blatant lie. Altogether his fix totaled more than $800, mine was $8 + shipping; and mine fixed the problem.

I hope this helped you guys! Good on you for trying to fix your own vehicles rather than blindly taking it to a dealership where you’re told to bend over and grab your ankles.