[mygatts57]

I need some advice. I have a 71 911 t which I drove about 5 miles to the pub on city streets this evening after letting it warm it up in the driveway about 5 minutes and it ran perfect - smooth and silky.

Upon leaving about an hour later on the same route back it ran like crap, including a very loud backfire while deaccelerating down a hill from 45 mph in 3rd gear!, not even after down shifting.

It does this a lot, it's like I have two cars in one.

Any ideas! Thanks