Stumbling/Shaking when coming to a stop

[PNUT8825]

Hey guys, I was hoping someone here can help me out. I just recently bought this truck and its really nice but there is something that is bugging me. When im coming to a stop and shift it into neutral the truck stumbles, it feels like it wants to stall and the truck shakes but when I actually come to a stop its ok. it only happens when i slow down to stop, usually around 900 rmps. Any ideas of what it could be?

 

[Viva*the*Ranger]

Interesting. I would start with your fuel system. Replace fuel filter and run seafoam. Cheap and a good place to start. Sounds fuel related to me.

 

[Earl43P]

Two things come to mind.

4.0's are prone to intake manifold vacuum leaks, which could be worsened by the large vacuum demand from pressing on the brake pedal (Brake Booster is vacuum operated). To rule that out, simply remove the big vacuum line to the brake booster and thoroughly plug it, then drive it and note whether the behavior changes with no vacuum feeding the brake booster. Then go find the actual vacuum leak.

Clean the IAC valve, since it controls the idle air flow. It is an electromagnetically operated piston on a shaft. clean it (and its passages on the intake). Once it's clean, actuate that piston by whacking the valve against your palm such that the piston is forced to travel along the shaft from the impact. Do it in both directions. It should make a satisfying thwock sound when you are doing it.