98993c2s

This problem is not only specific to 993s:

http://www.m5board.com/vbulletin/showthread.php?t=57536

FisterD

I would have to say a fix that lasts 20, 30, or 50K is one hell of a band-aid. That's like saying an oil change is only a band-aid, in 3-5K your going to have to change it again...new tires are only a band-aid, in 5-10K your going to have to replace them again......
If oil consumption is O.K, then just expect to do the flush every 20-50K as scheduled maintenance. Not too bad, if you look at it in those terms.

JasonAndreas

The MY95 has the same sensors and you can check the ports the same way you can on a MY96+. The difference is that the MY95 will only throw a code if the auxiliary air pump has a problem. MY96+ will also check the O2 sensors for a voltage drop when the pump operates and throw a code if that doesn't happen.

If we had caught it in time the EPA would have forced a recall (I tried) like they did for some other manufacturers (GM) that had moisture problems (partially from too much exhaust back-pressure) corroding the check valve.

Lorenfb

"The difference is that the MY95 will only throw a code if the auxiliary air pump has a problem. MY96+ will also check the O2 sensors for a voltage drop when the pump operates and throw a code if that doesn't happen."

Monitoring the O2 sensor/sensors is really the proper way to fully check the overall SAI system,
i.e. not just checking that the punp operates. and that's why it's in the OBDII spec (>= '96 993)
versus ODBI ('95 993).

Check here ( www.systemsc.com/pictures.htm ) for info on 993 SAI problems.

JasonAndreas

With a MY95 you can still manually check for an O2 voltage level drop when the pump operates it's just not (like you say) done automatically for you like it is with OBD2.

TCallas

So, speaking of a proper CEL (Check engine light) diagnosis, there is even more to think about now that you know about the oxygen sensor voltage drop when activating the Smog pump. You also have to know about the characteristics of the oxygen sensor voltages and what they mean when you do this. They have different personalities at different times and eventually, to confirm our diagnosis, we have to access the suspect valve guides by removing the valve cover and rocker arm including valve spring to see what the guide wear actually is. I disagree that the CEL is the only problem. With worn out valve guides you are dumping tons of oil into your exhaust system and contaminating the oxygen sensors and catalytic converters. Your engine would not know how to run properly without the correct oxygen sensor signals. There is a lot more to the story than meets the eye. These engines are very good about not smoking and not fouling the spark plugs while having severely worn valve guides so the customer is misled into thinking that all is well.