Idle Air Control Valve

[ltmark]

Desperately trying to find vacuum leak! One method suggested is to blow smoke into system via small hose after blocking off intake. Was happy and thought I had it until I realized all the smoke was coming out via (what I believe is a small bypass/vent on the back side of the IAC) Is that a "cap" a one way valve, so in practice, during IDLE operation, NO AIR CAN ENTER and create a leak or does that cap have to somehow be plugged to perform a smoke test?

 

[ltmark]

I just replaced IAC, idle better but still a little low. Still working on it..

 

[1955moose]

What dtc codes are you getting? Did you check fuel pressure? If smoke test not working, you could always try old school spray or propane.


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[ltmark]

NO CODES PRESENT. Since replacing the IAC, it idles much smoother, but I still feel a little stumble and definitely feel a slight miss/hesitation when accelerating at lower speeds. I rest the memory so I have to drive a little to see what the long term trims are doing. As indicated before, Bank 1 was lean and Bank 2 rich!

 

[ltmark]

Sorry. Yes, I checked the Fuel Pressure and it runs stady at 55-60 lbs

 

[1955moose]

That's high it should be 42-43 lbs. check your fuel pressure regulator. Pull vacuum hose if any fuel come out replace regulator. If regulator is working proper your fuel pressure reading goes up 5 pounds or so.. I have a 2000 expy that runs between 35 to 41, depending on key off/ running. Are you getting fuel smell/ dark color Exaust?


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[1955moose]

Just looked up specs. Yours should be 35psi plus or minus 5. Basically 35 to 41psi.


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[ltmark]

My book shows 55 lbs for the 5.4L (2V) 35-45 on the 4Valve 5.4L

 

[1955moose]

What year is your expedition? I looked up 2005 I think, that's A 3 valve. My 2000 expedition is 41 psi max. Maybe yours is right then. Anybody else want to comment on this.


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[1955moose]

Well I stand corrected it seems like your SUV does run higher. 55 is not high.


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