Any car guys/gals here? Need some advice

[Catch22Dem]

When I fill up my tank, after about 20 miles the car starts spuddering at crusing speeds (40-50mph @1200-1500 rpm) then the check engine light comes on. The light usually goes away after about 20 more miles, but this has happened for the last 4 fill-ups. The first time, I thought maybe I just got some bad gasoline, but now I'm really wondering what's going on.

[Oeditpus Rex]

1. Does this happen only when the tank is full?

And when the light goes off, does the sputtering also stop?

If this is the case, my first reaction is a vacuum leak in the tank, leading to low fuel pressure. Replacing the filler cap could be the fix, but first I gotta ask the make and year of the car, and the type of engine if you know it.

[Catch22Dem]

2. Yes and yes

If I accelerate it doesn't do it, and if I coast it doesn't do it. It only does it when I'm going down the road at a modest speed with my foot barely on the gas. It's a 2005 Chrysler T&C 3.3 liter V6.

Fuel cap would be great. Talk about getting off cheap. I was thinking about running to the guys at Advance Auto Parts to get them to read the codes for me.

[Oeditpus Rex]

3. Well, I'm only guessing

It's possible that it's that simple — it's happened before, and modern "check engine" lights do come on when the gas cap seal is bad or even just if the cap isn't properly seated. But I don't know if a 2005 Chrysler has a vented or non-vented fuel tank, and that makes all the difference. I do know it'd be unusual for a cap seal on a 3-year-old car to go bad, though.

So, unless you wanna take a chance on the cap, don't take my word for it — get the codes diagnosed. On modern cars, everything is computer-controlled, which makes troubleshooting from a distance even more precarious.