NateWithATruck

Hey,

I recently rebuilt the 5.8 Liter V8 EFI engine in my 1996 F-150 after both heads cracked. I wanted to save some money and learn how to wrench on my own vehicles, so I bought a Hayes manual and tore it apart. Two months later, I had it running and started driving it again. However, two quirks popped up immediately after the rebuild.

The first is that the AC only blows through the defrost vents onto the windshield regardless of the setting the dial in the cab is pointing to. The fan speed and the thermostat are fine and work correctly, but regardless of the setting, all of the air comes out onto the windshield....as if it was eternally on the "Defrost" setting.

Secondly, the truck idles very slowly. Upon starting, the truck will idle cleanly for 30 seconds....maybe a minute or two. Then, the RPMs start to drop and the engine begins to misfire. Then it dies. If you tap the gas before if dies, it springs back to life for 10-15 seconds and then returns to it's coughing and sputtering. This has been only an inconvenience at redlights until recently. After coasting for several hundred yards down a hill, the engine stalled out right at the bottom of the hill where the road began to turn. I lost power steering and ABS and almost put it through the ditch and into the trees on the other side of the road. Needless to say, this is becoming a potentially dangerous problem.

Any help, hint, and suggestions would be greatly appreciated.

Thanks
-Nate

wde3477

Welcome to the site!

Your HVAC problem is likely due to a vacuum hose failure. IIRC, there are at least three diverter dampers controlled by vacuum motors - not sure if the temperature is calbe or vacuum motor actuated - mine is a cable. Seeing that all functions are affected - suggest to look for the supply line coming off the intake manifold, going to the HVAC control panel in the cab - perhaps it didn't get hooked back up, or got pinched?

Suggest to inspect the Idle Air Control (IAC) solenoid for the idling problem. Make sure the internals are clean and the piston rod can move freely - carb cleaner will work fine. You do not want to fool with the throttle butterfly stop screw - the idle speed should be controlled by this solenoid.

Good luck, and keep us posted.

BigGreyBox

the idle will act up with a bad vacuum leak anyways. So that could be both problems. The idle and misfiring could also be from the timing being off.

waih136

I had the same problem with my engine idleing like that, it was the idle air control module. Was especially bad in winter, my advice is to clean it first to see if thats it if ya wanna save a few bucks, lasted a few months untill it started acting up again. Good luck