Anybody know why it does this

Ok I put a new valve cover gasket on my dd its an 89 f150 with 300 6cyl. When I got it back together it wouldnt start and run, got it running by haven a friend hold the throttle open a little while I did some checking. When I unplugged the fuel press. regulator from the man. vacuum portit would idle by itself but only at 450 rpms, if I put my finger over that port and plug the vacuum leak it will die. I was thinkin IAC but it tested good and thats the only thing I know of that would affect idle like that. I need to get this done so I can get to work. Any suggestions would be appreciated, thanx in advance.



Jason

sounds weird. but maybe it needs to be cleaned up. Its like the vacuum advance isn't kicking in or something. I don't know what to say about this as I'm getting myself confused. I'm just throwing ideas out there. Spray carb & choke cleaner in it and see if the rpms get higher.

Okay thanx guys, guess I'm gonna have to do this the hard way and just test everything Thought maybe this had happened to someone before. Its weird it will run without the IAC in place or with the fuel pressure regulator unplugged from the manifold vacuum port but not with both hooked up. Had a local technician tell me it might be in the EGR system so like I said I'll just test everything.

Think carefully about what else you disturbed while doing the gasket... what did you unhook, unplug, etc. in the course of doing the simple gasket job..

Many things could be the cause... just gotta narrow it down.

Hope this helps

When you say the IAC tested OK, does that mean you took it off and applied voltage? If it's working OK, you should be able to see the valve operate as you do so. They can get stuck with carbon and crap. Just scraping the crud away can make 'em work again......that is, if that's your problem. I'd look there, since the engine seems to need more air in order to idle (plugging a vacuum leak causes it to stall.).

No didnt apply voltage but did clean it and check the ohms and still does the same thing. I 've been working all weekend at night so havent really had time mess with it. Father inlaw is gonna come and help, he's pretty good at findin whats wrong and its usually something simple cause I'm tryin to over think it. thanks for the help.

Be sure to look for voltage at the IAC valve harness when the switch is on, too. Good luck.

Hey guys, I figured it out. It was the wiring to the IAC. The original owner who is a friend had wrecked the truck in the past and the shop that fixed it did a piss poor job of fixin it. I found a spot where the wiring had been hacked and repaired poorly, the wires were just twisted together and taped. All is now fixed with solder and shrink wrap. I HATE WIRING. Thanks again for the suggestions.