Christopher Zach

Well this has been an interesting week. After months of running flawlessly my 85.5 928S is back in basket-ville-land.

Started last Saturday when I swapped out the cruise control computer. Put a replacement one in, took it out on the road, CC worked! Lots of fun, accel and decel work, turns on and off properly and holds speed. Bit agressive on downshifts to make up speed, but not the end of the world.

Tuesday I take the car to work and notice it stalls when starting cold with no gas. Annoying.And it feels off when going from no pedal to full power, just stumbles a bit before getting going.

By Thursday the car will barely hold idle and when starts goes to 3k then down to idle then stalls with no gas action. Great......

So something is wrong again. I'm thinking it might be a vacuum leak, then I realized that the cruise control runs on vacuum. Then again according to the maps the CC should be behind the one way valve for the heater control. I pulled the black hose for heat control earlier this week and heard the vacuum depressurize so the vacuum is good in the tank and the heater control system. Maybe the CC is not plumbed in right?

Never dull. It was nice to have CC working for a day at least.

SeanR

Cruise control vacuum should be a separate system, but due to hacks working on them I've seen them all jumped in together. Doubtful that is your issue but should be looked at. Checking to ensure the fuel vacuum is stand alone should be easy by pulling the airbox and inspecting the lines and following them to the multi port connection under the MAF. The HVAC/Cruise system should not be connected to any engine side.

I'd start by looking at the Temp II connector/sensor and ohming that out. Then the MAF and MAF connection ensuring the wiring is not touching each other.

davek9

As Sean said it should be separate, however If vacuum is in question, just block it off at the closest feed from Throttle Body to Fire Wall connections to the HVAC and the Cruse system, break it down to the basic's and go from there.
Also this issue could be totally unrelated to your last fix and the ICV is now sticking from sitting if it's old?

Dave K

Christopher Zach

It's possible it's the ICV, the other thing that happened is that I had the doors all open and let the battery run down so it would not start. Recharged the battery, but did I either lose or corrupt constants in the computer? Maybe I should disconnect for awhile then reconnect it?

Weird that this all went bad literally the day after I was down there, the car's been starting fine for months.

C

Christopher Zach

What a weekend. If there's one thing about Porsches it's that you will eventually own every tool known to man, from a 16 pound sledgehammer to a jeweler's lathe :-)

For this I took the air filter out, there was a ton of leaves and junk on top of the filter. Must have gotten sucked into the intakes. So I vacuumed it off, pulled the garbage K&N filter, and started taking the top end apart.

Pulled the MAF and it had all sorts of small crap between the screens. Not good. And the sensor wires looked gunky but not broken. Went out, got a can of MAF cleaner spary, took off one of the screens, and proceeded to spray to from severl feet away so as not to damage the wires. Cleaned out the crap, replaced the screens, put it in, fired up, still stalls.Sometimes would hold idle for a bit then die.

Pulled MAF again and checked into the intake pipe: Lots of gunk and oil residue in there, cleaned everything out, sprayed maf cleaner into the port for the idle valve, put it together, fired it up, nope.

Pulled MAF again and started on the ICV. As usual the hose clamp screws were impossible to get to so I had to go out and get a 6mm 1/4 drive socket and a tiny 1/4 sized ratchet. That does it, and after an hour of tugging and pliers-ing the hoses I finally got it out. While there I stuffed paper towels in the intake, and used a vacuum to get all the crap out of the valley of death and the center area. Then I checked out the valve.

Gunked, so I cleaned it out with MAF fluid, put it back in without tighting the hoses, removed the paper towels (very, very important), put on the MAF, and engine started and happily idled at 2,000 RPM. Um. Whatever. Shut down, started up, yay and right up to 2k.

Shut down, took ICV out, sprayed a bit of WD40 into it to lubricate it going forward, put it together, snugged down all the clamps, got the MAF on again, put on the air filter housing, fired it up, nice 1k rpm idle. Which is still somewhat high, it used to idle at around 400 rpm but I'll take what I can get. Shut down and started a few times, let it come up to temp, then shut down for the day.

Also checked the vacuum, 17 bar at idle on the front fuel damper, which should be fine for government work. Actually a bit higher than before, I think it was around 14 before I started working on things.

Other problem: My battery is crap, it died again after leaving the doors open for 2 hours, read 11.75 volts open circuit. Charged it, checked voltage with engine at 1k RPM it's at 14.4 volts which is proper regulation. Shut down, battery is at 12.5 volts so it's crud. Will a M8 fit in there, I'm thinking of just getting an AGM and being done with it.

Hopefully this will fix it, but I might just buy another ICV so I can have a spare. And I'm ordering a proper airfilter, SeanBaby was right when he said these KN ones are garbage. Given the amount of crap in the MAF and body I can only imagine what this car has been ingesting....

Thanks everyone, Long afternoon but should be done. Now back to figuring out why the CC worked for one shiny day....

Christopher Zach

Darn. Hour later still will not start and go straight to idle. Need to pump it to get up to 2k rpm then it will stabilize.

Time to get new ICV.

Oh and the temp II sensor (blue plug) reads 2.2k at warm water temperature (sitting for hour after running) and the plug reads about 5.6k to the DME's.

C

Christopher Zach

And in the "man that was a bad moment" I went out to check the engine and it was completely *dead*. As in engine cranks, and no hint of fire. Felt really bad for a moment, then checked the Temp II sensor plug. I hadn't pushed it down all the way, so I did that and engine started. Still can't start to idle, can idle, but if you blip the throttle too quickly you can stall it.

Will put the car aside for the rest of the week and drive the 944S.

Hilton

Hard to idle, and dies when blipped sounds like its in limp-home mode (i.e. no MAF signal), which is a misnomer as its more of a "limp to side of the road" mode.

Simple test.. unplug the MAF and see if the behaviour stays the same, or get worse. If the same, then you have a MAF signal issue, which is commonly either the MAF, or frayed wires inside the boot on the harness side of the connector.

Oh - for those hose clamps on the MAF.. 18 or 24" extension, and a 1/4" U-Joint plus the 7mm socket works a treat.. just remove the passenger side fuel rail and you should be able to get to the hose clamp.. takes seconds.

Christopher Zach

Ok, will do next weekend. The wires were broken out of the rubber end on the plug but did not appear to be damaged. Likewise how badly would the car run without the MAF at all; I was able to drive it for a few days.

Also how is the MAF secured to the throttle body? It looks like a press fit into the aluminum with just a rubber ring on the inside providing a gap seal. If that's the case how in the name of heaven does it not come up with the air filter housing to the top of the MAF? Can't be that simple, or can it?

C

Christopher Zach

Ok, was nice today (snow tomorrow) so I checked the MAF. Here's the results:

Control: (Airbox off, airbox temp sensor attached, nothing else done). Engine started rough, would idle, die, finally got to idle at 800 RPM or so.
Remove MAF, plugged in. Nothing.
Remove MAF, unplug: Oh boy this is limp mode? Engine barely ran, hard to get above 1k even with 68 911 throttle toes (yeah I could start a Weber IDF/IDA in anything). It's probably not that.
Reinstall MAF: Same as starting.
Spray MAF cleaner into intake at idle. Makes the engine loopy, but settled down. Idle eventually smoothed out. Shut down, started, starts on the first crank.

I think the ICV was gunked, I cleaned it, installed it, then put some WD40 into it which is a stupid idea as the WD40 gunks it up (saw this somewhere here). Doing a second cleaning with the engine at idle (all air going through the ICV) cleaned it again and it's working better for now, but will probably suck again eventually.

I'll swap out the ICV this weekend and see how it goes. Got a cheapie $50 one instead of the $250 Bosch to see if this was it, did note the one in there seems not to be a Bosch and I did see evidence it was replaced in the past (flakes on the intake plating right where the screws would be) so I don't think this was the car's first Rodeo.

C