M104 PVC or IAC hose confusion - PeachParts Mercedes-Benz Forum

upod · #1 09-08-2017, 09:51 AM

I am re-installing the air intake after a head gasket replacement on a 1991 300CE with a M104.981 engine (straight 6, DUAL overhead cam). I got this car after another mechanic gave up putting it back together, and I think there are some missing pcv related hoses.

In the photo below, I am pointing to a long hose coming from the lower oil pan area....I am not sure where this hose connects to on the intake manifold or if perhaps it somehow connects to the IAC valve (idle air control valve). It is part of the PCV system but I am not sure where it is supposed to go. Anybody know?

The only other thing I am not sure where it connects to (possibly related to the hose above) is the inlet side to the IAC valve (Idle air control valve), shown in the photo below. I've seen photos online of the inlet of the IAC with a hose pointing downward below the intake, so I know it goes somewhere below the intake, but nothing else showing where the hose is routed to or from, so any help would be appreciated:

I've been to the dealer and they were unable to figure this out and suggested that I find another car with the same engine to compare it to, so hopefully someone out there has some experience and could point me in the right direction....THANKS!

Rcktsled · #2 09-08-2017, 03:05 PM

Where are you at in LA? I have a 92 300ce and live in Ontario. I'm not home but I can take a look tonight. You are more than welcome to come take a look under my hood this weekend if that would help.

duxthe1 · #3 09-08-2017, 11:18 PM

This is from memory..... but the first pic is a breather hose. Attaches between the 3 and 4 intake runner with more than is pictured.

Second pic the "S" hose is backwards, cold start valve sits in one of the taped over holes. The other side of the idle valve attaches to the air flow meter housing, not pictured, with another hose and barb fitting.

FWIW, almost none of that needed to be disassembled to do the head gasket.

upod · #4 09-09-2017, 10:37 AM

Rcktsled, I'm at least an hour away from you but I pm'd you.

Thanks Duxthe1 for clarifying some of this. It has opened up some areas that I need more clarification on, however.

On the plus side, for anyone else with this issue, I've figured that the inlet side of the Idle air control valve goes to the black plastic bottom of the throttle body housing, as shown in the photo below:

MY REMAINING QUESTIONS ARE:

QUESTION (i):

The orientation of the 'S' Shaped hose with two air nipples. The factory diagram shows this orientation:

But when I connect it to the idle air control valve, there's about a one inch gap between that hose and the "wing" shaped hose, as shown below, so this does not appear correct to me...unless I have the wrong idle air control valve in there (because the factory diagram above has the lower port of the valve facing the engine and the higher port of the valve facing away from the engine:

QUESTION (ii):

What do the two small nipples in the "S" shaped hose connect to? The factory diagram (shown earlier) has one nipple with a 90 degree barbed fitting, which I'm missing. OK, I can get that piece, but what hose goes into that fitting and where does it connect to at the other end? Same thing with the other open nipple, that does not have the 90 degree barbed fitting.

QUESTION (iii)

There are two nipples on the intake housing around cylinder number 3 that I don't have connected to anything, shown below:

I'm assuming that perhaps one or both of the nipples in the "S" shaped hose connect to these or that PCV hose that I show in my first post, coming from the lower oil pan area. However, I'm puzzled as to what goes where, and could not find any help at the dealer with these connections either.

duxthe1 · #5 09-09-2017, 01:05 PM

The "S" hose has one hole for the 90 degree nipple that connects a hose to the top nipple between 3 and 4. The other smaller hole holds the nipple of the cold start valve. IIRC that smaller hole should center between the two threaded holes nearby

Something does look weird about your idle valve and hose config. Is the "S" hose sound under all the tape?