Hello- My 1996 960 (California car 176k miles) failed its emission test. It is running lean according to the test results. I have already replaced cat and both 02's which didn't change the readings at all. What could be causing it to run so lean and thus being classified as a "gross polluter" here in ridiculous California?

Any advise is appreciated.

 

You most likely have unmeasured air entering the intake. That means a air leak somewhere after the MAF. Most likely a bad intake gasket, which is common on this engine in that era.

But start first with the vacuum hoses and the brake booster hose. Simple stuff always first.

After checking the vacuum hoses, then I would do a compression test.

But I would bet it is the intake manifold gasket.

DanR '94 964 388,000 miles (154,000 on the new engine)

 

Hey Dan, those 960's also have those short intake hoses that come loose sometimes as well, don't they? I think I have read that people clamp or zip tie them secure?