964 will not start after fuel fill-up

[JJAYALA]

Hello everyone,
I am having a problem that I hope is simple but could use help. I have a 1991 Porsche 911 C4 which was running fine until I went to the gas station the other day to fill up the gas. The car had been sitting in garage for about 3 months prior to that. It started fine and mu first trip was to the gas station.
After the fill-up the car tries to start but engine shakes violently and turns off. I tried starting the car with the gas pedal all the way down and it works and can be driven but it stalls if I come to a stop.
I also noticed that it starts and runs better if I take of the gas cap. This seems to be pointing to the Gas Bleeder Valve but wanted to check if others have had this issue and found a solution.
Thanks

[rattlsnak]

I assume you didn't put diesel fuel in it?

[JJAYALA]

No, I did not put Diesel Fuel in the car. As a matter of fact the gas station where this happened does not sell Diesel at all. I did not use any additives either. Any other ideas on what the issue could be?

[chrisbruck]

Does the station get much traffic? I tend to shy away from the smaller mom and pops that look less busy simply to avoid getting old gas.

[JJAYALA]

The station is very busy and modern. Have not heard of any complaints and tons of people I know use it.
I wish it as that simple but the problem seems to be in the car and not the gas itself...
Thanks to both rattlsnak and chrisbruck for answering, I know these are the first diagnostic questions to look for. If you have some ideas beyond those I would greatly appreciate it.

[FPB111]

Phase separation of "Gasohol". If the tank was not full when it was parked and it had gasohol in it additional condensation can cause the alcohol/water mix to drop out of suspension and cause the type of problems you are experiencing.

[kodioneill]

Take a fuel sample put it in a jar let it stand for an hour and look at it check for contaminants.

[rattlsnak]

I hope you realize I wasn't trying to be a smart-ass, but if the problem happened immediately after a fill up, then that is the first place you need to look. What changed since it ran good versus it running bad? As noted above, you need to pop the fuel line off at the fuel rail, have someone crank it over and fill a glass jar with a least a quart of fuel and let it sit for a few hours and see if there is any separation that occurs.

[JJAYALA]

rattlsnak, thanks for the clarification and I assure you I did not take offense from your comment. I actually asked the people at the gas station if there was a chance that Diesel had been mixed in the fuel somehow so again, it is a reasonable diagnostic question.

I will take the advice and take a fuel sample to see if there is something going on and let you know what I find.

Thanks for the help.

[kodioneill]

At Watkins Glen a couple years ago I was at a driver ED and followed a guy in a c4 down to a local gas station in town I was behind him he filled up tried to start the car fired up stumbled and died and it was a well visited station the results were contamination and water. I went on to another station.