Problem after filling my gas.

[Zero07]

Hi everyone and thanks in advance for helping me out. So here's my story, I'm on my way driving in my "2001 Toyota Corolla S" to work when I realize my tank is half empty. So I decided to pull up to a gas station too fill it up. I never let my tank run 3/4 empty cause I here condensation can be developed. Anywho I fill up on gas and I'm standing waiting looking at the meters and thinking man is this car good on gas. Finished filling it up pop the gas cap back on, got inside my car, started it up, and my idle speed seems to be struggling. it goes from 800 down to 400 repeatedly sometimes causing the car to shut off. I drive for like 30 seconds come to an intersection and it's fine. What could of caused this to happen???
Please help me out.

[fishexpo101]

If this keeps happening, then it might be a problem. From what you decribed- it sounds like either some bad gas, or in the process of filling - it temporarily clogged the sock filter on the fuel pump.

Double check that everything else looks OK - it is entirely possible that it was just a coincidence that the problems starting happening after you filled up the car, could be from something entirely unrelated to the refilling event. Check fluid levels, check the air filter, clean the MAF/IAT sensors, clean throttle body, pull the plugs and read them, look for missing or damaged vacuum hoses.

[Zero07]

I don't believe it would be bad gas I've always filled up on gas at reputable gas stations like Esso. 87 Octane is what I fill it up with I'm not sure if I would fill it up with 91 Octane I'm not sure if it would make a difference or solve the problem. After running the car for like 15 seconds on the road the car goes back to normal, it's been really confusing me cause it only happens when I fill up the tank, never when I start the car besides filling the tank would the problem occur. So I am convinced it's during the process of filling up on gas. I've checked my fluids and there fine. The air filter is in great shape, I've cleaned the MAP Sensor with Electric contact cleaner, havn't thought about cleaning the throttle body or checking the vacuum hoses I'll get that done on my next day off.

Appreciate the time and help!

[fishexpo101]

Does it do this every fill up? If it does, it could be a EVAP related issue - if the tank is not building pressure and properly trapping fuel vapors - could cause some problems. But nothing that should manifest as funky idling. Only things that I can think of off the top of my head is a vacuum leak at one of the VSV valves by the vapor canister - but again, it shouldn't cause any idling problems and even a tiny leak will set a CEL almost immediately. Or a faulty fuel pump (wiring or dying pump) / fuel pressure regulator - both are part of the fuel pump assembly that is inside the tank - have to pull up the rear seat to get access to the cover panel above the fuel pump assembly.

Try cleaning the throttlebody and double checking the vacuum hoses for leaks - a clean throttle body has a big influence in idle quality and stability. A clogged IAC valve on the bottom of the throttle body could cause idle instability - but nothing would do that immediatly after a fill up.

[Zero07]

Yes every fill up it occurs. So if the tank isn't building enough pressure or trapping the vapors, the only time I can think of when that would occur is when I remove the gas cap, could it be possible that the gasket might be damaged? I'm gonna check everything that you just mentioned I hope I can find the problem it's been bugging me lately.

Thanks for the help Fishexpo101 I'll be sure sure to give u a heads up on my results.

[Foxone]

I know this is an old post , but mine was doing the same thing. Mine turned out to be the front VSV next to the airbox.