I recently replaced an o2 sensor and put in new plugs gapped to .044. The car ran great for 3 days then the past 2 days the car intermittently has a rough shaking sound under the hood while driving, the engine doesn't seem to be affected, I think it may be the fans rattling. Also, today, the heater was intermittently heating. The blower always worked, but for 10 minutes it wasn't blowing hot air. I turned off the heater, turned it back in a few minutes later and worked fine. Just wondering if there's any correlation here.

When I shut the car down, nearly everytime, it diesels for a couple seconds. It just sounds bad, and I've never had that happen before what is the cause for this? Could an intake manifold with a gasket that isn't properly sealed cause this?

 

isnt dieseling caused by knock?

which is caused by low octane fuel?

 

If the OP is referring to dieseling, as knocking or commonly stated as run on after turning off the ignition I would agree on the low octane. As for the lack of heat, I would suggest to check your coolant level as it may be down a little or possible you have an air lock and need to be bleed out ... my 2 cents on things

 

Your dieseling isn't bad. We have a tractor that can only be killed by popping the clutch in a high gear
I don't think I've seen a modern fuel injected car do that, though.

But the no heat is air trapped somewhere. I just popped the radiator cap off in the morning, started the car up, let it warm, revved it a few times to blow out the air, and replaced however much coolant was needed. No troubles since and my buddy did the same with his Z.