Hey guys, got a 1987 F150 302 AOD 4x4 that will stumble then surge and sometimes stall when placed in park or neutral after being in gear. It will only do this when cold, the problem is worse in colder temps.

Only code right now is 44 - Thermactor system fault - this is due to my disconnecting the smog pump until I can install a new diverter valve. Has been this way for over a year.

I did a fuel pressure check a few months before this all started and everything was within spec except the pressure bled down as soon as the fuel pumps shut off. Cleaned the IAC the other day too - no change.

Also, this just started right before I drove from Montana to Michigan. Got 12-15 mpg fully loaded doing 70+ the whole way so it does not seem to be affecting fuel mileage. The truck runs great in gear all the time and does not surge at all once warm (20 mins of driving).

Where should I be looking to solve this?

Thanks!

 

With the fuel pressure bleading down so fast the fuel pressure regulator needs to be changed. That might also solve the problem.

Also, some 1987 EFI models had a heat shroud on them (mine does) like the carb motors that would take heat from the exhaust up into the air intake until the motor warmed up. With this problem only happening when at start up on cold days it could be hard to find if the fuel regulator don't fix it.

 

New FPR fixed the issues with idle. Also increased mileage 1-2 mpg all around. Hope this helps someone with a similar issue.