2003 Buick Regal rough idling

The bolts cannot be re-used in this engine. They are one time use.

Installation Procedure

Use compressed air in order to blow oil out of the tapped holes in the cylinder head.
Lubricate the ends of the push rods with new engine oil.
Install the push rods to the same position on the cylinder head.

Install the push rod guide plates.

Install the valve rocker arms.

Notice: This bolt is designed to permanently stretch when tightened. The correct part number fastener must be used to replace this type of fastener. Do not use a bolt that is stronger in this application. If the correct bolt is not used, the parts will not be tightened correctly. The system or the components may be damaged.

Apply threadlocker GM P/N 12345493 (Canadian P/N 10953488) or equivalent to the rocker arm bolt threads.

Notice: Refer to Fastener Notice in Service Precautions.

Install the valve rocker arm bolts.

7.1. Tighten the bolts to 15 Nm (11 ft. Lbs.).
7.2. Use the J 36660-A to rotate the bolts an additional 90°.

Install the left or the right valve rocker arm cover.
Inspect the valve train for noise.

You also have a coolant temp sensor problem that can dramatically change the fuel mixture.

There are dozens of possible causes. You need to correct the ones you know about first. After you have done that do both a wet and a dry compression test to help narrow it down.