Ever since my car was new it has a rich idle after filling the gas tank. The first time I really noticed it was on a trip to Florida where the engine would stall after filling the tank and re-starting it. It happened several times but usually it just sputters a little and smells like gas. Now that I have a AFR gauge it's very easy to see what's going on. Everytime I fill the tank and re-start the engine it idles at 10:1 AFR for a minute or more. If I rev the engine or start driving it leans out to (~14.7:1) where it should be. I'm sure it has to be caused by the evaporative system but I'm not sure exactly how or what t might take to fix it.

BTW, I don't top-off the tank. When the pump shuts off, I don't add any more gas. Also, this occured when the engine was bone-stock and has continued so it's not related to the larger injectors or turbo. I'm curious if this is a common problem for XBs or specific to my car only.

 

Seems in a way what was going on with mine, my car was dumping fuel in, and go into limp mode as I was saying in the other thread. Whats going on SCION!?!?

 

What you had reminded me more of when my AFR sensor went bad. The difference is that I had a code for "AFR sensor stuck rich" in addition to the P0172 you had for "bank 1 rich".

What's happening at fill-up seems to be related to the evaporative system that uses engine vacuum and a charcoal canister to purge gas vapors from the tank. On a lot of cars it's common to soak the canister with gas when over-filling the tank. This extra fuel is then drawn into the engine through the evap system, resulting in a rich condition. However, I'm not over-filling at all and the rich condition is only at idle and very slow speeds. It clears up quickly once I get moving.

Has your car ever sputtered, stalled or smelled like gas after filling the tank?

 

With the car just sitting, especially on a warm day, fuel vapor will travel to the canister and be stored (doesn't require tank overflow). However, the resulting rich condition on engine start should clear very quickly. To have it show up regularly at idle suggests a sensor problem to me -- either O2 or MAS. I'm presuming the idle speed is not dropping excessively low.

 

I'd suspect a sensor too if this happened at any other time but this only occurs immediately after filling the gas tank and it happens every time. If I let the engine run while fueling, it does the same thing. It's as though extra fuel is being drawn in through the evap system but only enough to affect idle. If I rev the engine or drive away, the AFR returns to normal. I wonder if a full tank has any effect on fuel pressure?

 

Damn, your last sentence is what's resonating with me -- an FPR problem? You say it only hits immediately after filling the tank, but pump pressure wouldn't explain it, whereas an FPR issue could. I'm trying to imagine how a canister purge malfunction would stably create that behavior at idle, but I just don't see it. Any significant charcoal canister affects should be very short lived, even with open valves, the fuel injection should easily overshadow the evap tank following engine start.

Still, if the evap valves remained open, it would certainly result in a small reduction in the A/F, though I would expect it to be modest. For it to cause your engine to stumble or even die seems excessive, especially if it goes away following the initial fill-up behavior . Why would the Evap valves stay open immediately after a fill and then eventually close? Makes no sense to me! A fuel pressure regulator issue seems more likely. Speaking for myself, engine behavior is the same immediately following fill up Vs immediately before running out of fuel.

 

It is possible that the purge solenoid is stuck open slightly.

 

Trevor, just to be clear, the car hasn't actually stalled in over 2 years now but it does still have a very rich AFR immediately following a fill-up and I can smell gas in the exhaust. The problem with the FPR theory is that this only happens immediately after filling the tank which still leads me to suspect the evap system. The idle AFR is never rich at any other time. I don't know, this is a weird issue...

DezodDon, thanks. If the purge solenoid were stuck partially open, could that account for the rich AFR occuring only immediately after filling the gas tank but at no other time?

I suppose I'll have to make data log the next time I fill up and compare fuel trims before and after at idle. I could also try squeezing the evap vacuum line closed while it's idling rich and see what happens. Thanks guys.

 

My logic was that if the pump fuel pressure runs a little higher immediately after fillup and the FPR wasn't regulating it down properly, then a higher pressure could get to the injectors resulting in a rich condition. In any case, hope you figure it out!

 

Your logic seems sound to me and I'm certainly not discounting it as a possibility. If I ever figure this out I'll be sure to let you know what it was.

 

hay guys I"m running into the same problem with my 08 xb
DezodDon were is this solenoid??? that would be something I'm looking first for a replacement. and has anyone found something that fixes this is problem

 

FWIW my car still idles rich immediately after filling the gas tank. The engine doesn't stutter or stall and I wouldn't even know it if I didn't have a AFR guage so I've just accepted it.

How do you know your engine is idling rich after a fill-up? Do you have a AFR gauge?

 

don't really know that my car is running rich by a gauge only by the random rich code, and I'm just having the same issues with stumbling after a fill up

 

It's probably the same rich condition as my car and most likely others or even all XB2s. I'd like to know what's causing it but since it doesn't stall any more and corrects itself once I get moving I guess I'll live with it. It's not like I can take it in for warranty work with a turbo.