Just a thought ... does your 993 have an O2 on R and L banks> If so ... swap them and confirm that O2 sensor is getting the correct signal.

Assuming you have an air pump pushing O2 into air injection nozzles. If so, is the pump operating correctly ..? meaning is it pushing to much air into one bank pre O2 and setting up the lean reading?

I have had some success watching Foreign Car Service in Alexandria pump smoke on one of my cars [E30] to see that it was the oil return tube under the intake manifold going back to the block. Would have never thought to check for air leaks there ... those machines are great ... to bad are so $$$.

Sorry, don't know details of the 993 motor but have certainly futzed with 2nd-ary air injection systems, etc...

I have four O2 sensors, one pre and one post cat on each bank and there's no way to mix up the wires. The plugs are unique to pre and post and the wires aren't long enough to go into the wrong side. And all four O2 sensors are about 700 miles old.

RL I'll be down in a week and will bring my LM-1, which has a wideband 02 sensor that we can screw into each post-cat 02 sensor bung. That'll tell us exactly what your AFR's are for each bank and we'll know for sure if you have a lean condition.

I think the lean condition is determined by the O2's reaching maximum enrichment.

Rick: from a Rennlist list I'm on for 964s: "[Mine had a similar problem.] I checked every vacuum hose I could locate without success. Our local expert used a smoke generator to pressurize the intake system with smoke and located the problem in a few seconds. One of the rubber sleeves that connect the intake distributor to the intake manifold was cracked allowing air into the induction system. The defect in the sleeve was not visible to the eye. After replacing all of the sleeves the idle returned to a steady 800 RPM. An easy fix."

Hmmmm. I'll have to ask Taylor if he tried the smoke test and if not, take it there for that. I think I'm gonna take my injectors to IMA for a serious cleaning.

IMA is a good place for the injector cleaning. :)

You've inspired me to take the CIS apart on my '76 for some air / oil leaks:

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:)

It taking my intake off were that simple, I'd do it too. Pulling my engine requires an alignment afterwards. I'm probably headed for a smoke test and injector cleaning.

Do you have a vacuum guage? If so, you can connect it to the intake and try to find the culprit. When under load your engine moves a bit here and there unless you are running solid mounts. With the vacuum guage connected try wiggling any hose connected to a vacuum source. Last time I chased one down it took a couple of days. I was so frustrated after a few hours I gave it up for another day. I had tried propane, soapy water, etc. and finally found it using the vacuum gage and wiggling the crap out of the hoses. Funny thing was the gage was showing normal until I wiggled the right hose and the needle wiggled. The source was the connection to the power brak booster. It did not leak while running at idle sitting still. I am convinced the only way I would have stumbled on it was the wiggle.

Matt DeMaria has one. 301 948-6762.

Saw somewhere where somebody took and wet/dry vac, put some water and dry ice in it and made one. They are very expensive units.
ARF