I just discovered something: The engine will die at idle if the oil cap is not on tight. I was pulling an oil sample in advance of my 3 year service tomorrow and fired it up with the oil cap loose.

 

I'm not at all surprised. My '78 Saab is the same way. Loose oil cap or dipstick not fully seated will do it. I used to see that back when I had a shop. Oil caps on the "B" and "H" engines had a cork gasket and if it tore or cracked, that was the symptom that brought the customer in.

 

Must be some sort of pressure sensor.
Many moons ago I did an oil change on my car in the garage, it was dark by the time I finished, and I put the oil cap on by feel.
Next morning, driving to work, after about 2 km smoke started pouring from the engine bay.
Long story short the oil cap had fallen off about 1 km back (I eventually found it on the road) and oil had been splashing out of the filler hole all over the engine bay and on to the extractors.
Obviously that car ran perfectly OK with no oil cap!

 

On the old Saabs it wasn't a sensor, at least not directly. They were K-Jetronic and didn't have too many. If memory serves it was the introduction of unmetered air to the engine leaning it out. The system could adjust to a point (at least the ones with lambda) but it was a bit more than that.

 

No oil cap = no crankcase pressure = funky engine vacuum.

 

Sure, go and get all technical on us.

 

My thoughts would be the same as Lizzardo, surprised that F Type is effected by this.

 

I think the PCV system keeps the crankcase under vacuum. When the oil filler is removed it allows air to be sucked into the intake manifold through PVC system and it confuses the ECU.

 

It certainly did that. It also lit a fog lamp failure warning as well. (???)