FeedNfrenZ

I've just puchased a (1985) 928......... it has a few issue one of which is the exhaust smells like it is running rich on fuel. It also starts and idles erratic when cold. ie. almost dies from low idle then kicks up to 1500 rpms then repeats until warm then it idles relativly smooth around 500 rpms.
I suspect that I may have more than one problem. I was thinking the O2 sensor as far as running rich. I saw on another posting that there was a suggestion of Mass Mass Sensor for a similar problem. I went look at the Air mass Sensor........... Is it possible that someone could have installed it Backward? Up side down? Would it cause a problem if it was? How do you tell correct orientation?

John Speake

If you look on the black side cover on the MAF, you will see an arrow showing the correct way for the airflow.

Basically, if you can see the two slots in the flange nearest the airfilter housing, then it's in the correct way around.

MAF always age to give a weak mixture. This could cause your cold running problem, because the O2 loop isn't active then

FeedNfrenZ

Thanks, John. I know the slots your reffering to. pretty sure they are near the airfilter housing.......... will check ASAP.
Any way to prove if MAF is bad without replacing? One other piece of the puzzle. I noticed allot of oil on top of the intake manifold also down inside the large opening where the MAF mounts.............. may be time to have a profesional pull the intake???????????????

dr bob

Most of the stuff you can smell is raw fuel and maybe NOx, which often has a foul rotten-eggs odor if it's real excessive. Raw fuel often happens as a result of lean misfire, and the high chamber temps of a lean mixture also point to a lean mixture. Couple those two to the poor idle, and you are looking for a vacuum leak. It doesn't take much.

Start by isolating the known vacuum users like the little X-manifold fitting by the brake booster. Put a cap on that so that HVAC leaks are isolated. Then go after the hoses in the engine bay, the connectors for the throttle and the MAF, etc. These are common failure points thanks to age and heat, and should get you attention before you start swapping in expensive EFI components like MAFs and brains.

John Speake

Hi,
There's no easy way to check MAF calibration, without a test jig. The MAF needs to be within about 3% accuracy for the car to run properly under all conditions.

I'm sure someone on the list who has swapped their MAF for a new one recently could lend you their old one, which was probably running OK before it was removed.

Alternatively, you can borrow a rebuilt one from my US agent.

FeedNfrenZ

Thanks guys for all the good info. Found a vacuum leak in the heater bypass valve............ I've replaced it. Still have cold start problem.
I'll do some more vacuum leak hunting ASAP........... damn work.......... get's in the way of the really important stuff.......... like my car!
I've purchased a Mytivac Vacuum tested...... can I simply plumb it into the vacuum system and observe the Vacuum while running? What kind of a reading should I expect? Is there more than one Vacuum loop to look at? Or is there just one vacuum loop for all of the Vacuum operated systems?
Also.......... Is the MAF a high failure item?

heinrich

If there is oil drooling from your throttle body, pull the MAF and hold WOT and insert a clean rag, and if it is loaded with oil upon extraction, you need to fix the dastardly cam cover breather conumdrum. And I would then recommend not making any high-G sweeping turns until you've rerouted or fixed the cam breathers.

Rich smell from the tailpipe could be many things, but often is leaky injectors. If the cats glow when idling a while, then you need to fix the fuel leak immediately as cat fires happen and can be destructive.

FeedNfrenZ

I do have a good bit of oil on top of the intake manifold and down inside the large hole where the MAF mounts. Haven't been able to identify it's source yet.

heinrich

When I bought my S4, it looked as if someone had poured oil over the intake plenum. There was oil everywhere, dripping and the engine looked as if it was ready to die there and then. I soon discovered that I had two oil leaks. One, the oil filler neck and two, the oil cooler lines. After replacing the lines and sealing the filler, I have never had a single drop of oil again on top, around or under the car.

The thing with oil in the throttle body and especially for an '85/6 around the plenum, is that it very very likely means that oil was backfired into the plenum (if you can call it that). And that would mean major cam cover oil ingestion. Not really unexpected or a big problem unless you ignore it.

SteveG

heinrich: there is a lot of discussion about oil here. A small amount, say up to 1/8 inch in bottom of plenum is not unusual and harmless. A vacuum line connects to the drivers (US) side plenum and a mist of oil finds its way in. If enough accumulates to find its way into the intake, you could have a problem.