This is my experience too, it is better to have the O2 sensor connected if the rest of the system is functioning correctly. You can set the WOT AFR for max performance and the system will correct the cruise AFR to stoich for better mileage and longevity. You cannot get both of these with the O2 sensor disconnected. You may have to live with a slight oscillation at idle, but if idle performance is your goal, why have a Porsche ?

Well, the lambda is still in operation despite the O2 sensor being disconnected.

My issue with the O2 sensor was that it created an annoying stumble at constant acceleration. For example, in third gear running at 2500 RPMs I could feel a slight stumble or "trailer hitching". The sensor was new too. Maybe it wouldn't bother most people but it got on my nerves enough that I disconnected it.

I think that this is a result of the sensor constantly trying to correct the mixture and not doing a very good job. I have heard this complaint from numerous people on this forum. I guess that is why a lot of us run without it.

You should be able to pretty much tune the lambda-frequency valve idle oscillation out when you make the closed loop mixture adjustment with a dwell gauge hooked to the test port.

There's also a degree of adjustment to when the system goes from closed to open loop when driving by slightly rotating the switching device (forget what it's called) on the side of the throttle body. The Bentley book has most of the diagnostics to follow to check its function.

Brian

No, "lambda" means stoich and the system can only get there with the O2 connected. The FV is still working with the sensor disconnected, but the "lambda" part is all about bringing the mixture back to 14.7:1. When you disconnect the sensor, the system is in default mode and goes to a duty cycle based on a new engine with perfect compression. It cannot correct to stoich.

Your problem is probably a vacuum leak or a worn out distributor, not that the engine cannot cruise at 14.7:1.

I wouldn't overlook the condition of the distributor as a factor. As I said earlier, in my case, the distributor was in unbelievably poor, gummed up, sticky condition. The mechanics my previous owner paid to the tune of thousands (I've got the stacks of receipts) to shotgun the hell out of stuff certainly never bothered to check it out.

Also, take a hand-held vacuum pump and check the retard and advance action of the distributor. (I know, I know, most owners disconnect and plug the retard line.)

Brian

Unfortunately, the distributor is a mechanical device that wears out much quicker than most people realize. The springs lose tension, the idle timing give a false reading and it can't hold a steady spark at cruise. Most SC's have vacuum leaks at the injector sleeve outer O rings and at the worn throttle shaft.

If you still have a cat, the O2 sensor keeps it alive, and you can expect to replace it sooner if you disconnect the sensor. If you have an aftermarket exhaust and don't care about fuel mileage because the car never really goes anywhere, disconnecting it to satisfy an anal idle speed issue is less important.

Yeah, that is what I meant. Thanks for clarifying.