[Mac-Porsche]

Sorry for posting yet again on this topic!... Been trying to tackle these CIS issues since finishing a full rebuild for past 2-3 months... Losing it on this...

1981 911sc - US model
What I did during rebuild...
- Split crankcase - had oil pump rebuilt, sent all various components to machine shops
- Installed 97mm P&C set, 10:1 CR
- reground camshafts to 964 spec
- ignition distributor (including vacuum advance) rebuilt
- fuel distributor rebuilt
- fuel injectors cleaned and inspected
- new airbox with pop-off valve (previous one discovered cracked/blown on bottom)
- new intake boot
- SSI heat exchangers installed
- New oxygen sensor

Engine fires up great since rebuild. No oil leaks. Fires right up every time, hot or cold. Revs really nicely.

However... idling has been a problem since finishing rebuild, surging idle... Bought fuel pressure gauge, checked all fuel pressures (system, control, etc) - all checked good. System pressure was showing 65psi (~4.5 - 4.7 bar), so I put in a brand new fuel pump since it was on the low side (for good measure). At this time, I thought maybe it was bad fuel. Emptied gas tank completely, blew down all fuel lines, replaced fuel filter, put brand new fuel in. Also replaced spark plugs (old ones were black and oily - thought maybe they were fouled). Surging idle still persisted...

Around this time, it was running so rich that it was sputtering raw fuel. Did the "baseline" calibration, where I pulled a fuel injector and leaned until no fuel from injectors when pump is on. Got it running/idling much better, but my wideband O2 sensor (Innovate LC-2) meter showed it was running very lean (16-18 afr) when warm.

Frustrated, I finally took it to a well respected local Porsche mechanic. Hooked it up to smoke machine to check for vacuum leaks - no leaks. Then hooked it up to gas analyzer - showing ~5.5 CO%, which I was told was way too high. Reduced the CO% down to ~3.0 with mixture screw. Also adjusted the idle speed to 950rpm and double-checked timing - all good. Afterwards, 'seemed' to idle better, but I did notice some slight surging before I left.

Immediately after leaving shop, car stalled twice on the way home. Which had never happened before. Both times were from letting off gas after acceleration/high revs. Letting off the throttle immediately would cause the car to drop to very low idle (~400 rpm) for a couple seconds before picking back up to where it needs to be. Sometimes, it would drop as low as 200rpm and stall (as what happened twice on the way home).

Read on these forums that it's a sign of running too rich. Pulled the fuel injector and ran fuel pump, looked good. Hooked up Innovate LC-2 sensor which still showed 16-18 afr at warm idle - so that adds more confusion...(starting to not trust that meter)...

Not sure what to do anymore... I feel like I've literally tried everything... Is there any other good gas analyzers or AFR meters out there? I did notice that the Porsche mechanic changed the fuel mixture without the car warming to temp and without disconnecting the oxygen sensor. Plus he set it to ~3.0 CO% as mentioned before - where the Bentley manual suggest to set the '80 - '83 models to 0.4 - 0.8 CO% with oxygen sensor disconnected. Could this be my problem? If so, shouldn't the lambda system correct that when hooked up?