2004 Tahoe 5.3L 4wd. Vehicle runs great at all time except after getting gas. When I attempt to restart after filling up it stumbles, sputters, and dies. Only way to start (without getting under the hood, see below) is hold the pedal to the floor, start, then quickly drop RPMs to about 2k for 10 seconds.

I know what you are thinking because I thought it too. Canister purge valve stuck open, but not so!

Tested purge valve at the intake and valve tested good (both electrically and the diaphragm). Wiring is fine with +12 volts on the pink with key on and the ECM driver controlling ground via the green/white. When valve is closed I can hold vacuum (external tester) without any leaking for long periods.

No codes/CELs/MILs when driving the vehicle.

If I get gas, then pop the hood and unplug the electrical connector (vent line still attached), vehicle will start and idle perfectly. As soon as I plug it back in, vehicle runs rough, sputters, and dies. I can feel the valve start pulsing on and off as soon as I plug the connector in.

If I follow what I just outlined above but add the step of raising the idle to about 2k, while plugging in the electrical connector, and holding it there for 10 seconds after putting the valve in operation, then all is well again till next time I need to fill up. Sometimes when doing this procedure, CEL will light with a P0443 code, but only when I'm manually unplugging and plugging in the electrical connector, not while I'm driving the vehicle in between fill ups.

Any ideas???

 

Idle air control valve?

 

Thanks for the reply. Thought about the IAC, but seems to be working well under normal driving conditions. If there was a problem with it, wouldn't it be acting up all the time?

 

Yes, it will cause issues other than at idle.

 

Right, understand, but I mean if there's an IAC problem wouldn't I notice problems at times other than just after getting gas? The only time there is any issue at all is just after refueling. Every other time it runs great, smooth as can be, at both idle and off idle.

 

When you fill up, is it that, fill up, or just add gas? I reread your post about this just happens when you get gas. Need to isolate this issue, try not filling all the way. If that doe's the trick, we need to isolate it further, I'm thinking into emissions issue.

 

Emission problem or vent issue.

 

Anytime I add gas regardless of how full the tank ends up. Also, I never overfill the tank. I was instructed to swap the purge valve (despite being certain that mine is working) so I did. Swapped it yesterday with a buddy who has a Suburban (same purge valve). I then went to get some gas as a test. Added only four gallons which ended up putting the level just a bit under 3/4 of a tank. When I restarted, the same problem occurred.

Once I floored it to restart, then idled around 2k for about 10 seconds, I then drove away with it running perfectly again. Did a couple of hot starts yesterday as I ran errands, and then a cold start this morning and, as usual, everything was just fine no issues starting or driving.

 

Is it possible you have a plugged vent line?

 

Nope. I checked and it's clear as can be and the vent solenoid is fully operational (and normally open anyway).