193K miles check eng light came on last night coming home from work--was running fine, starts right up, no problems. Drove to work this am, still fine and afterwards, ran by Auto zone. Code came up 0440 could be gas cap. Noticed over the last 3 fillups, when I would open cap, lots of pressure blowing back--never has done this before. Put new cap on and drove around for 30mins, no issues. Filled up 30mins later and upon startup and driving away, it got very rough and could not keep an idle. Starts right up, but wont hold an idle. Thoughts?

Well, car was in an accident about 5 yrs ago, front end with deer. It was repaired by local body shop and no issues since. I decided to look at the charcoal canister up front and its an AC/Delco unit!!! I dont believe they came like this from Sweden--bet he had one lying around and charged for a volvo unit to insurance. Regardless, the canister had about 2oz of fuel in it and that cant be good. Tried to dry out, but cant get apart so I will attempt to get a used volvo or a new gm one since it worked for this long. BTW, I always top off when filling up and Autozone said this is probably the reason.

This is the very reason that I do not top off any of my vehicles any more, it's too easy to get liquid fuel in the charcoal canister. It is only designed to handle vapors.

DEWFPO
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1998 S90 083,228 and 1995 964 154,100

It idled before you replaced the cap right? Put the old cap back on and see if the problem goes away.

Do you know for sure it was Pressure when you opened the cap and not Vacuum? If it was pressure you would have had a very strong odor of gasoline, not so if it was vacuum.

DEWFPO
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1998 S90 083,228 and 1995 964 154,100

You/ve got a problem with the tank vent/charcoal canister system. See if the canister is full of gasoline-you just may need to replace it. Check the FAQ (in the drop-down from the "more" box above) for tips on troubleshooting this system. See if the car will idle with the gas cap off.
sredwine '94 940T at 237K, '96 960 at 154K