Need Help Diagnosing Rough Idle and Stalling

[Harry97]

Good Morning

I have a'97 4.0 4x4 w/ 100k miles that has surging idle and sometimes dies when coming to stops/shifting from D to R. I have replaced the vacuum lines, TPS, MAF and IAC. None of these have significantly fixed it. It does run better when the MAF is disconnected. I have also watched O2, and fuel trims and they are very similar between bank 1 & 2. I also have a lean code for both banks. Any help would be great!

 

[franklin2]

Some of the early 4.0's had faulty intake gaskets.


Ford 4.0L V6 engines (OHV and SOHC) frequently experience intake manifold gasket failures, often addressed via TSB 98-6-8 (specifically for 1997 models) regarding gaskets sucking into the runners, causing vacuum leaks, lean codes

and rough idle. Updated gaskets with better material, such as Victor Reinz gaskets using HNBR and FKM rubber, are recommended to handle high-temperature, high-pressure environments

 

[Harry97]

would this be the upper or lower gasket? I have the plastic upper manifold off and that may be the issue. Otherwise it’s all coming off at some point to fix a valley oil leak.

 

[franklin2]

• TSB 98-6-8: Addresses a specific issue where the gasket between the fuel supply manifold and the lower intake manifold loses compressive loading, requiring a redesigned gasket.
• Repair Procedures:
  • Cleaning: Thoroughly clean all old gasket material with a non-metallic brush; do not use power tools.
  • Material: Use updated gaskets (like Fel-Pro or Victor Reinz) designed to withstand thermal cycling and, for later models, potential fuel degradation.
  • Torque Sequence: It is critical to tighten intake bolts in the correct sequence to ensure proper sealing.
• Engine Coverage: These issues are particularly prevalent in 1990-2002 applications, including the 4.0L OHV and SOHC engines