Engine wont stop

[corolladiy]

My engine after sutting off the ignition will keep on turning on it's own. I dont know why the hell it keeps doing that but I think it's because one or two of the cylinders always fire prematurely? Or I've also thought it could have something to do with the fuel mixture and igniting under the compression?
I am really worried because this will keep continuing anywhere from 1-4 seconds after I turn the car off! and I certainly dont hink it's good for it in any way...

any ideas would be greatly appreciated

[SCT]

The problem you have is called Engine Dieseling which is basically the engine still able to combust on its own possibly without the need of a spark. It can be a bad fuel mixture (too rich) and/or wrong timing. Adjust either or both should be good. It can even be carbon deposits that are glowing hot and act as an ignition, but I doubt you have that.

What engine do you have?

[Donald]

Check your timing first, it is probably too far advanced.
If that is good, change your gas station to one on the Top Teir List < toptiergas.com >.
There is a difference in gas from different oil companies.

[corolladiy]

Okay so this is what I have done to correct the problem.
4-AF Engine/ CA, US SMOG/ 200K miles
I turned down the idle which was too fast to begin with to the normal 650RPM or so. and that started to work immediately towards stopping the dieseling. Also, the higher octane gas helped too but the car now jumps and skips and misfires under acceleration (sounds like a popcorn machine or a rotarty) which is a problem I never had using just regular gas (I used mid grade this tank).

The engine will seldom diesel now so I don't think a re-timing will be necessary but I know that a very important vacum line that starts right on top and on the center of the valve cover is missing a very small spring... This vacum tube ends right at the bottom of the carb and at the start of the intake manifold. I'm thinking I could just go to pick n pull near where I live and pick another valve up on the hunch that none of the engines will be messed with...

[Ghostyman]

I'd recommend trying to clean carbon deposits out of the combustion chamber. They might be picking up enough heat to continue to ignite the air/fuel without spark. Seafoam is the standard advice you'll get over the Internet and I'll also recommend running some ATF as a cheaper alternative.

What part of the Bay Area are you in?

[Angel13]

I have the same problem with my 89 corolla which is sometimes it will take like 2 second for it to turn off. I basically think that it may be my carb that is going bad.

[Frozentide]

Its likely carbon deposits due to the age of the engine. I wouldn't recommend running higher octane gas, just regular gas from good gas stations.

I remember covering this in class a couple months ago, so I'll check my notes tomorrow and see what other info I can find for you. I'm training to be an Automotive Technician.

[Angel13]

Ok thanks i would like to now more about my problem