968/92

A month after aquiring my 87 S4 I still did not find the cause of my intermittent idle/stall issue. I took the car yesterday to my non Porsche specialist mechanic to see what he thinks. He diagnosed it to be the PCV on the passenger side cam cover (both). If I blow into the one closest to the firewall (air going into cam cover) there is resistance but if I hold pressure the air passes in a couple of seconds. The other one air goes straight through. It seems a good explanation to my issues but after I went home to research how the PCV system works specifically on our 928s it seems that these two "pcvs" are not supposed to work like this. Am I correct that they are not one way check valves like almost any other car on the planet? We also found a plugged red and black vaccum line at the passenger side near the firewall, we removed the plug, no vaccum when engine running and we couldn't figure out where it is supposed to plug.
I was full of joy when I thought we finally figured it out

Here are my symptoms btw:

1-Cold start it idles at 800 rpm. If I give it gas and let go rpms dips a bit and comes back up. Seems to run rough and doesn't rev fast but doesn't seem anything excessive.
2-As it warms up two scenarios may occur. Either the rpm rise slowly to around 1100-1200 rpms and runs smoothly. Or it starts to sputter with revs slowly going down until it stalls. If I give it gas while it's doing that the revs dip very low and stalls most of the time. The rpms hunt sometimes in the second scenario as well.
3- In either scenarios, it pulls strong all the way to red line without misfires. I drove it for 6 hours in scenario 2 when I first got it while putting it in neutral and keeping revs above 1300 rpms when I need to slow down or stop.

What I've done to try to resolve the issue and other hints:
1-Noticed flappy wasn't flapping. Vacuum was not hooked up correctly on the booster side and the line for hvac was not plugged snug enough. Flappy is flapping now.
2-Tranny vac line from intake was not holding vacuum. Yesterday while it was on the hoist, I noticed the vacuum line going into the modulator was cracked on its end. We cut it a bit and plugged it. The line holds vacuum well now from the intake side.
3-We hooked up a smoke machine to the 5 way connector yesterday and did not see any leaks.
4-It had an intake refresh by a long time Porsche specialist this summer.
5-I routed some straws into the opening of the icv into the intake and did my best to make it go into the icv and not go the other way, sprayed a lot of brakclean in and cycled from idle to just of idle a bit to let the icv open and close multiple times. No difference noted.
6-Idle switch clicks off idle
7-O2 sensor was disconnected when I bought it. Connecting it didn't seem to make any difference except that it dies (in a different kinda way) if I unplug it while engine is running.

Really hoping somebody can put me in the right direction.

worf928

Post your general location. Maybe we can find you someone that is at least familiar with 928s.

There's so much wrong in your post that I don't really know where to start except this:

Did the car exhibit this behavior immediately after "a long time Porsche specialist this summer" did the intake refresh? If so, he wasn't a specialist.

If not, what work was performed after which the behavior started?

There are no PCV valves in the cam covers. There's only one thing remotely like a PCV valve and it's in the oil filler neck base.

I can't imagine that you can get enough smoke through the 5-way connector to perform an adequate smoke test. Maybe you can.

Based upon the description, you have a Automatic and you have disconnected the vaccum from the shift modulator. Your shifts will now be violent at all loads. You need to get this hooked back-up very soon or you will snap the driveshaft in the torque tube.

968/92

I'm located in Ottawa Ontario. I bought it a couple of weeks ago, symptoms were already there when I bought it. I guess those two fittings in the attached photos are just 2 way breathers from the cam cover to the intake? I was hoping he has something to connect the smoke machine to the maf directly, will probably look for someone with the right equipment. The line to the modulator is plugged back to the modulator and working properly after we removed a small portion of it where the crack developed.

Mrmerlin

temp 2 wires at the connector look exposed,
this should be fixed if that is the condition,
replace the connector and cut the wires back to fresh wire,
then fit a new connector with boot.
Test the temp 2 sensor as well

968/92

Photos is off google not my 928. TEMP II tested forgot to mention.

Mrmerlin

OK its always helpful to post pictures of YOUR car/engine or what your working on so a more complete diagnosis can be made

968/92

Here's my engine..

Mrmerlin

well there is your problem,
the aircleaner is upside down....

dont swap it around it already has dirt on one side so keep there,
in the future the hump points to the sky.

fraggle

lol that's my engine. I believe I fixed that connector.

And those elbows have no valves.

968/92

Thanks! New filter shipped. I highly doubt that this is what's causing my issues though.

Today I tried disconnecting the temp II sensor while engine is running. I expected it to shut off but nothing happened. Tried it again while engine is cold and nothing changed also. Not even a slight change in engine rpms or anything. I tested the temp II while removed and in a cup adding hot water and also at the connectors of the ezk and lh. Same resistance at the sensor and connector. I expected that with the Temp II connector unplugged, the LH should read infinite resistance and enrich the mixture. Should I assume my LH/EZK is on the way out and is just running a back up map for the mixture?
Any other tests I can do to confirm? I guess the best way to confirm is to switch my ezk/LH with a known working ones so if there is anybody near Ottawa that can help me out I would really appreciate it!