shaking after buying gas

Hello everybody!
Just got a "new" 1999 4Runner SR5 4WD (V6), 116K miles.
During a test ride everything was fine, just beautiful.
On the way home stopped for gas at BP.
Filled it up with regular gas. After that the engine started working very roughly, shaking, almost stalling at every traffic light stop. What went wrong? Has anybody experienced this kind of problem?
Thank you for your help!

 

My 22re will knock and ping like crazy on reg. I only run 91 octane. The compression ratio on a 22re is around 9.5 to 1. If u can, siphon off half and fill it up with the highest octane u can. Worth a try. If it still runs rough then at least you've eliminated the problem being the fuel. Good luck!

 

Thank you, BestGen! This would be just great. I hope you are right. Tomorrow I'll try what you suggested. I hope my mechanic will have a tank for siphoned off gas. I'll report the result.

 

I forgot to mention that the "check engine" light came on.

 

What's your timing set at? You shouldn't ping on 87 unless you've got your timing really pushed. If you're under 10 BTDC and pinging on 87 octane you might have trouble brewing.

Also, low octane won't cause misfires and stumbling. Bad/wet gas will though. Try a bottle of Heet or STP Water Remover. Parts store will have it.

That makes it easy, pull the trouble codes. It'll probably come back as misfire on multiple cylinders.

 

That makes it easy, pull the trouble codes. It'll probably come back as misfire on multiple cylinders.

Thank you, Utah, for your reply! This is what I think too -- looks like misfiring cylinders. But why all of a sudden? Is it possible that BP's methanol content is too high?

 

Kindly disregard my previous msg.

 

Anything is possible - maybe they put the wrong fuel in the underground tank, or maybe it's just bad/wet gas. Or the fact that you filled up before the trouble started could be sheer coincidence, and you've got some other trouble. Pull the codes and go from there.

 

This morning it started just fine. So the fuel is not the problem. Drove for an hour, stopped for 15 minutes. After the stop the problem came back. The scan showed 1st cylinder misfire. Maybe it's an injector's fault. I'll try the injector cleaning fluid. And tomorrow my mechanic will take a closer look.

 

I found that tweaking/moving the coil pack assembly (the front left one) fixes the problem for some time.

 

Front left, is that plug one? Sounds like you found your trouble!

 

Yes, it's #1. Thank you for your help!
Tomorrow I'd like to change spark plugs anyway, along with oil change etc.
This truck is fun!