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Dieseling in 30,000 mile 2005 Honda Civic, manual transmission

Why does my car not turn off completely after I shut it off? It only keeps running for less than a minute. Can it be the timing belt at only 30,000 miles? Could it be the cheap gas I put in it from a Global gas station?

No timing belt issue

In regards to the “cheap gas” is it just happening on this one tank of gas? Has the “cheap gas” been used up and the condition continues?

Out of warranty? no “check engine” light? any recent work?

This issue must be resolved,my guess is it is related to the emission system (smog control)or a damaged spark plug.

Does it just keep running more or less like normal or does it just cough and sputter for a few seconds?

On a car this new, an ignition switch problem is really all I can think of.

I think it is out of warranty, it has been more than 3 years since I bought it, no check engine light, the throttle plates were cleaned but that did not change the problem, haven’t tried eliminating the cheap gas yet…

it runs more or less normally

Are you sure the engine is running, or is it just the cooling fan? (Have you looked under the hood to see if the belts are still turning?)

it sounds loud enough to be the engine, haven’t looked under the hood

Well, assuming that it is the engine that actually keeps running, it pretty much has to be an ignition switch problem. Have you tried jiggling the key when this happens?

Dieseling used to be a problem on older carbureted cars because as long as the engine was still turning, it could still suck fuel out of the carb and so if combustion was still happening from residual heat it can keep running until it cools off. With a fuel injected car, though, as soon as you turn it off the fuel injectors shut off as well and so it can only diesel on whatever’s left in the inch or so between the injector and the cylinder, which I would guess is probably enough for a second or two of sputtering, but not much more.