Definitely a wealth of knowledge going on here, thanks!
For clarity the vacuum sensor =MAP sensor? .
I checked the vacuum sensor and found it airtight. And in doing some research I came across the idea that a partly clogged fuel return line could give similar symptoms. Hmmm. I added a bottle of Techtron to the gas and sucked on the vacuum sensor and the odd thing is the car ran pretty well, not great, but not miserable. I can't imagine that Tectron and testing the vacuum sensor cured my woes, well maybe the Tectron, but still that seems too easy. Especially for a bottle bought off the shelf at Pep Boys.
Although the leaking maifold gasket has merit due to having just replaced the exaust manifold with a header. If I were to check that by sraying WD-40 around the manifold and listening for a change in rpm's, would it work given that the engine is running rich due to an air leak, not lean?
Thank you all very much.
Jonathan