I own a 1991 Trans Am GTA with a MPFI 305. Here recently after I changed the oil I filled it up with 5 qt. of 10w30 High Mileage oil and then started it. When I started it the oil wasn't pumping through the engine for about 2 seconds and then it kicked in and the oil pressure went up to 60 and ran fine. About a day after that I can here knocking in the engine when it is sitting at idle. And when i open the hood and mess with the throttle body I can here it knock and about 2800 rpm it sounds like it wants to send a piston through the block. Any ideas what engine part that would be?

 

What is the oil pressure? If the oil pressure is low it could be a bearing that has caught and spun. Otherwise my guess is it could be a carbon knock.

Hard to tell without more information.

Drain the oil and look for sparkles in it. Or remove the oil filter and cut it open and look at the filter.

 

The oil pressure at idle in drive or reverse is about 28 psi. The oil at netral or park is about 32 psi. And the idle while driving is variable. From 28-60 psi. But never anything below 28 psi. I've kept my eye on the oil pressure gauge here recently after the oil change.