Hey everyone,

I own a 1998 Ford F-150 with an 04 4.2 crate engine and a 5speed. The engine has roughly 150k-180k on it. I'm really at wits end with this engine. Some people swear by these 4.2's such as a 4.6 but I just can't ever see it.

Anyways, this truck for past eight or so months has been giving anyone who drives it trouble. While driving if you throw it in neutral to coast to a light for example, it'll just stall, but won't stall at idle. While the truck is idling at a stop it's roughly 950 and has a vibration to it. When idling while moving, in neutral for example, is at 1350ish. I pulled codes and got P0401 EGR insufficient code so I cleaned the EGR, replaced the DPFE, EGR Solenoid, speed sensor in the diff(only helped for one night), and the EGR tube that runs from the exhaust manifold to the EGR. I pulled the IAC and cleaned it and put a new gasket on. I pulled an IAC off a junkyard 98 3.8 Mustang and the truck ran much worse, as in stalling whenever the clutch pedal went down. The truck has ok power but no where near what it used to be, or what it was the night I changed the sensor on the top of the diff.

I'm starting to think that the isolator bolts need to be changed as an idea. I can't even remotely think of what is causing the stalling. Another issue with this is when downshifting I now have to double tap the pedal instead of a larger or longer holding of the gas, but that also varies on driving style. I'm stumped on this issue. Could the computer be going bad, the truck does have 300ish thousand on it?

Thanks for reading! This truck runs six days a week so I unfortunately can't afford any down time.