I'm already running 91 octane, we don't have higher octane pump gas here.

I emailed Steve Wong to find out if they have any thoughts but the chip seems like an unlikely culprit based on what I've heard and how ubiquitous they are.

88 , 3.2 liter engines don't have EGR valve.

I just called the shop here that I'm planning to use for this car (The Stable), they think it's plausible that it just needs a new cat. I'm going to bring it in Friday morning and they will diagnose further.

They told me that the speed sensor is not associated with the DME, it should be no factor.

My understanding is NOT to use a 93 octane chip here in Cali, as our octane is 91, as this might
cause engine damage. I ran into this situation when I purchased a 93 octane chip and was told
not to use it for these reasons, so I didn't.

Serge

Good info on not using the 93 octane chip in CA. You could buy some octane booster for the test. A Cat has to have a good fuel mix to be efficient and you're running rich. Don't get me wrong. You may have a weak cat but it needs further and complete diagnosis.

The Stable. Sounds expensive. Make sure they have a 5 gas exhaust analyzer. If not you may want to reconsider your shop for this repair. Anybody can slap on a fresh cat and an O2 sensor to make it pass. This is a classic smog failure repair instead of a thorough diagnosis.

I was thinking about this: what's the point of an O2 sensor if the mixture is manually adjustable? Shouldn't the O2 sensor be feeding the appropriate signal to the DME so that it can adjust mixture? I guess I can imagine that this is a coarse adjustment, and then the sensor provides input to fine-tune it. Just curious if someone can explain this. Thanks!

Basically that is it. The air flow meter is the baseline adjustment and the O2 sensor fine tunes the mixture.

New cat, passed smog with almost no measurable emissions :) The shop told me that Porsche doesn't make an OEM cat for these cars anymore, and the after-market replacements are fine but they won't last 25 years like an original. They said they have been doing more of these replacements lately as the original cats are starting to wear out after all this time.

I emailed Steve Wong to discuss the chip I have. He recommended switching to one with a 91 octane map, and offered to throw in a chip programmed with the stock map for free, since I don't have one. So I went ahead and did that, and I'll sell the 93 chip on the classifieds here. He said the 93 chip vs. 91 would have no impact on emissions, but if the rest of the system (i.e. the cat, etc.) was old, a stock chip would give a larger margin for passing smog. I haven't switched them yet, though, and I passed fine with the 93 chip. In terms of using 91 gas with a 93 chip, Steve said that the risk is that there would be detonation/knocking under heavy load or hot driving conditions. So it's not like every minute I drive the car with the 93 chip I am doing damage to the engine, but for the long term it's better to switch.