^^ X2.


The lower air flow of Idle increases the ratio of 'unmetered' air causing higher fuel trims. BUT - it seems you confirmed that here:


You say 'a bit of a vacuum leak'. That is in a way confirmed by your readings too. The leak is small enough it is being compensated for by elevated long term trims - and short term trims are normal.


Similar symptoms (and diagnostic technique) isolated an IM gasket leak or cracked plastic IM on my 2004 5.4.

 

Okay izgaryizgary I'll do that tomorrow and thanks F150Torqued


. I have two questions though number one I noticed on one end of the air plenum there's a module with two wires coming out one side what is that?? just curious, and number two if I do need to get a new manifold is there any other manifolds that I could use besides the factory stock. I've heard that Lincoln Mercury 4.6 manifolds fit but they don't seem to have whatever that module is

 

I'm not familiar with the 1997 4.6, hope someone who is will chime in on those questions for you. I would just say - a sensor located in the air plenum would probably be either an air flow sensor or intake air temperature sensor.

 

Can you post pictures - one of the whole plenum with the module circled and one a closeup of the module?

The module in the intake tube closest to the air filter box is the mass airflow sensor.

You are best off with a stock aluminum truck manifold.

http://www.ebay.com/itm/OEM-97-98-F1...JXVg6A&vxp=mtr

 

F150Torqued & glc I decided to do some research on what that plenum module is, turns out it's actually a butterfly valve that proportions the air inside the plenum neat huh.." the post that I got this information from goes into great nerdy depth on how the valve similar to some Porsches lol. I guess that rules out the Mercury manifold.. I'm not really sure how much that little valve is actually needed but the computer would probably lose its mind if I didn't have it so I'm going to go with a plastic one for the truck

 

Man I gotta' tell ya - I don't know WHAT THAT CONTRAPTION is if the manifold @glc linked in the prior post is for your truck.


Are you sure we're all talking about the same kind of engine. That looks to have come off an 'inline' block engine.


The 'sensor' thing in the photo is probably an intake runner control valve - and yes the computer would puke if it isn't there. But I would have to add - the component in the photo I would not call an air plenum.

 

That's the lower plenum and it's a IMRC. I linked an upper plenum.

 

Like I said .




Thanks