hi Guyz quite few times i noticed when i am refilling fuel for my lexus ls430 and the rpm goes up to 2,2.5 and comes back down to 1 or less and i get that feeling like the car is going to switch off but no it kinda vibrates a bit for a few seconds while filling the fuel and then its fine and normal ...what could be the reason for this?

need spark plugs replacement or ?

 

You refuel the car while its still running?

 

what grade gas are you pumping

 

Yes the engine is running while refilling and plus i use the Special Fuel ( 95 octane) and we have super which is 98...

 

Turn the engine off when refueling and the problem will go away. I believe cars are designed to have sealed fuel systems when they are running. You are probably confusing the engine control logic by having the fuel cap off.

 

+1. The gas cap is suppose to release pressure, but if the cap goes bad, it throws a check-engine light. Same thing here, if the cap is off, the system is going to detect too much variance in the sensor and the car will just do crazy things. If the problem is not exhibited when running normal, then it's not an issue.

Not sure why OP is even running it with engine on, but hey... it's his gas that he's running.

 

1. Refilling the car with engine running is dangerous - in some states it is actually illegal to do so 2. The car's air/fuel system is designed to be run as a sealed system so with gas cap open it is not running as designed.

Not sure what the benefit is of running your gas engine while filling with gas?...I guess the main objective would be to keep the heat or AC going. Definably not worth the small but real risk of causing some kind of fire. With the engine running the Cat under you car can run at 800 degrees F plus - the flash ignition point of gasoline is -43 degrees F. A gasoline pump nozzle fire will definitely put a crimp in your day.

 

i would imagine it has to do with the fuel going in and the vapor going through the charcoal canister and then back into the intake. since it is pushing fuel into the tank the vapor is going to escape any way it can. as the vapor goes into the intake of the car the air flow meter is reading an unusual reading and trying to compensate for it.

 

I suppose it will make it a bit more exciting if you're feeling a bit bored that day..... In all seriousness though, shut the engine off while refueling.