MEFI-4 Idle Hunt at Start Mystery

[km1125]

That's interesting. Does that hose go right to manifold vacuum?

[Delorean6855]

QR_BBPOST That's interesting. Does that hose go right to manifold vacuum?

Yup, it's the oddest thing.

[bud37]

Pull that hose off and see what is in there......this could be the reason the engines are having trouble controlling idle because of the unmetered air screwing with the map and iac unless there is something at the other end of that hose.....always a higher vacuum at or near idle with the throttle blades closed. With the blades closed the engine should be getting its air thru the IAC valve port and around the throttle blade assuming the blade stop is set correctly. This is the reason you will have to get someone to hook up and read the IAC counts etc if you want to find out what is going on and correct without throwing parts at it.

Maybe wrong here, but IF the ECU was designed to work with a PCV valve in the covers of each engine then they should be there. See if there is evidence of the PCV valves being removed for some reason.

[km1125]

Does that hose look original on either engine? Is it possible that it was replaced and the old hose had an inline PCV valve?

[Viper]

QR_BBPOST Finally getting back to this... so this is where the PCV valve should be...I remove the hose and it's just a hose barb.

nopcv.jpg

Super weird... the 6.0 schematic says the engine should have one.

pcv.jpg

....

is it like that on both covers on the same engine?

BTW, take a closer look at that fitting that looks like a hose barb. Some PCV valves look exactly like that at one end and are threaded in at the other and look like a simple fitting.

[Delorean6855]

Thanks everyone for the suggestions! Really appreciate it! I'll check these items this weekend. Hope to eventually solve this mystery. Had her out on the ocean this weekend and everything else is within or on spec. (I love when my temps stay at 172 even at 4k RPM!) I suspect though that I will have to drop some coin and get a scanner...just wish they weren't so bloody expensive!

[Delorean6855]

Pulled the hose off…doesn’t look like its anything removable. Hose runs to the top of the manifold. In other news, i have a refrigerant leak in my forward AC system. I wish I could solve problems faster than I pick up new ones.

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[bud37]

I am curious, try something......put that back together, start engine and pull that hose back off the valve cover and see if there is a big vacuum leak in the hose or just a trickle and does the engine react to it......

The other valve cover hose goes to the flame arrestor, correct ?