96GL Cold start up revs up and stalls

[96GL]

Need to verify if I'm on the right track here. 96 GL, 2.5L V6, Duratec, 112k miles. On a cold start up it revs to about 2000 rpm then dies. Starts right up again and if I feather the pedal can keep it running until it warms and then it runs better but still stalls intermittently. There is a hissing sound right at the IAC (Idle Air Control Valve).

Checked codes. P1518, P0133, P1131, P1151, P0300, P0171, P0174

Installed new MAF sensor, sprayed throttle linkage with brake cleaner, found and replaced broken hose (the one that comes from the air intake hose just past the MAF and run towards the front and into the intake manifold), order and installed new IAC.

Reset CEL. Started and same issue as far it revs up and then stalls out unless I feather the pedal. Hissing sound at the IAC. Can put my finger and feel the air at the IAC housing that the electric plugs into. Only threw one code this time. P1518 (Intake Manifold Runner Control fault - Stuck Open). I believe the new IAC they sold me is bad. Took back and they have ordered me another. Will be here in 2 days. Sure hoping the IAC solves it. Anyone else have any other ideas?

[jonmark1985]

The hissing noise, and unstable idle makes me think of a vacuum line.

[G O R T]

Yes, check the vacuum hose that comes out from under the UIM and goes to the PCV valve. There are several lines that can leak but this one is carries hot crankcase gasses and is prone to collapse.

[96GL]

Thanks guys. I had done an extensive search for any vacuum leaks or collapsed hoses by checking all the lines and actually found 2 and replaced. Including the line from the PVC to UIM. It's wierd I know but the hissing is actually coming from the IAC valve housing. I can put a finger on it and stop the sound and feel the air flow.

[G O R T]

[QUOTE=96GL;25910]Thanks guys. I had done an extensive search for any vacuum leaks or collapsed hoses by checking all the lines and actually found 2 and replaced. Including the line from the PVC to UIM. It's wierd I know but the hissing is actually coming from the IAC valve housing. I can put a finger on it and stop the sound and feel the air flow.[/QUOTE]

The IAC has a vent hole for the plunger but it should be covered, and should not be hissing.
It may well be damaged.
Luckily they are not expensive or hard to replace.

[96GL]

You guys were absolutey right. New IAC came in, installed, same issue. While it was some what idleing I was feeling around the IAC were it was hissing again and my finger touched on this vacuum hose that goes from the top of the intake to the brake booster. OMG I found the hissing issue. I was way off before. Called the Ford dealer and read the part number from this hose to them and they said that is a dis-continued item and that I can just replace it with a rubber hose. So a trip to Schucks and I'm back in business.

This solved a couple of problems I was having. For one the idle is back to normal, no more CEL and the brakes had been really hard to stop even with new pads are now functioning back to normal.

Thanks for the good advice. Hissing sound means vacuum leak somewhere as you mentioned before. If you can't find it keep up the search. It's there somewhere.