has a diesel effect

[bigchevyc30]

ok i have a 1980 c-30 with a 366 big block in it sometimes when i shut it off the truck will still keep turning itself over and over like some diesels today it did it for like 30 seconds when i shut it off what could be causing this or has anyone else had this problem

[1979C20]

Really advanced timing would cause that.

[biscuit41]

I'd check your idle speed as well...

[Lt.Del]

advanced timing--retard timing (after checking).
hot spark plugs--get cooler set.
Vacuum leak--check for leaks.
remedy can be using a higher octane, but, that is just covering the problem up.
Can also turn engine off in Drive, then, once off, switch to park.

[bigchevyc30]

i thought shutting the motor off in drive was bad for it and it did this with the old motor also i have heavy duty platinum plugs in the truck also for my spark plugs they are different from what i had in the old motor which still did it to. ive checked and my truck has no vacuum leaks.

[topp]

It can also occur from carbon deposits in the heads or on top of the pistons....

[jaredts]

I don't know all the possible reasons, but I've seen it a few times from people turning up the idle speed stop screw to compensate for vacuum leaks.