It only goes in one way.

I've sprayed carb cleaner on hoses when the truck is idling (MAF unplugged of course) and the idle comes up when I spray it where the brake hose goes into the intake, but I can't find any leaks! Would a leak not even allow it to start at all?

 

Ran another random test. If I hook up the MAF and breather assembly, but disconnect the IAC air feed that comes off the breather so that it is wide open at the IAC, and I plug the hole at the breather connection, the truck starts and idles (a very poor idle). If I stick my finger on the IAC air supply inlet back there, it sucks real hard, indicating the IAC is open.

 

A vacuum leak wouldn't keep it from starting.

You have to find that vacuum leak back there - as there HAS to be one there, it sounds like.

 

Wait. If I induce the EGR valve with the MAF off, it idles good. If I open the IAC air feed to atmosphere (with MAF on) it starts and idles. Wouldn't this all indicate that I'm being starved of air and that when new air is introduced it works better? If I had a vacuum leak, wouldn't I be too lean?

 

i would do a continuity test on the MAF wiring i would double check the MAF connections and the direction of the MAF installation and if all that checks out put it all back together and reset the ECM by disconnecting the battery and touching both battery cables together and holding for .30 seconds. Than reconnect the battery and fire it up. i promise you will this will not hurt a thing it just gets rid of anything learned by the computer since factory because the ford ecm is a self learning computer.

 

OK just tried your suggestion yogi, and no difference.

I've also thought maybe the fpr was stuck open, so I started the truck by disconnecting the IAC hose, and disconnected the vacuum supply to the fpr, which killed the engine and wouldn't allow any throttle response.

I also went out and loaned a scan tool and I am getting no codes.

 

Very bizarre. I'm out of ideas.

Air getting into the intake without going past the MAF means it would go LEAN like a vacuum leak. Or that the MAF value is so far out that the PCM gives up.

Is the PCV valve flowing?

 

sure is.I can take it out of the valve cover and it sucks on my finger when the truck is running.

 

If I let it run with the IAC hose disconnected, it will idle, but will get close to dying some times. When that happens, the EGR valve opens and sends the RPMs up to "rescue" the dying engine.


Also, the exhaust during this idle doesn't sound healthy (but neither does the idle), and it feels hotter than normal. Don't know if thats a clue or not.

Also, if I drive it in this condition, the power brakes are worthless, and the surging of the idle is so intense that its basically inoperable. Hitting the accelerator makes the truck jump like a high torque monster.

 

you won't get codes now until after about a week of running because you just cleared them when you reset the ecm.

 

Well I've been checking for codes all day with my "experiments" and haven't gotten any except when I disconnected the IAT, Cam Pos sensor, and TPS. Disconnecting the coolant temp or the MAF doesn't throw a code.

 

If your driving it, and lock it in 2nd or even 1st and gun it then let off, you have no brake booster?

Sounds like a major league vacuum leak.

But we've been over that, haven't we?

 

There's GOT to be a vacuum leak there...

 

Well the huge vacuum leak is induced though. In order to get it to idle and "drive" I had to disconnect the bypass hose from the breather to the IAC. That thing is sucking air like nobody's business. If I have it plugged in, it won't even start.

 

OK I lied here. If I have the truck running with my induced vacuum leak, if I take the vacuum supply off the fuel pressure regulator, it doesn't die. But if I try and rev the throttle, i get little to no response and the system goes lean for that second, but continues to idle.