At first start up, it runs fine. After driving for awhile I turn it off. After starting it up about an hour later, it starts shaking and running very rough until I rev it up and keep giving it gas. Then it will clear up and run fine until it's shut off and the cycle is repeated. Not sure what it could be. However, it first started doing this at the car wash. I just got it back together after pulling the passenger cylinder head to fix a broken exhaust manifold bolt. Not sure if any of this is related, but I'd thought I'd just throw that out there. Whatever it is, it's not consistent. I've checked the vacuum lines and I see nothing amiss. Also, not sure if it's related (probably not), the primary cooling fan won't come on unless the AC is on or unless I unplug the temp sensor. Replaced and tested the new sensor too. It tested good. Help!!