Last night I installed new OEM spark plugs in a 1990 Regal 3.8L (165K miles). The engine now turns over faster.

Now I noticed that the car shudders between 45 and 55 MPH. Anything below or above that and everything seems fine.

Any ideas?? Could it be the oxygen sensors?

Sounds like you have a problem with the plug wires.That happens alot after a plug change on older wires.

~Larry~

Usually make it a habit to replace plugs and wires at the same time.

Also, check to make sure you've gapped the plugs to 35 thousandths(.035) before installing them.

Another common problem when replacing spark plugs, especially if they're hard to reach, is accidentally cracking them while installing.

Thanks for the reply.

I thought the gap specified is 0.06. Is that not correct?

Thanks,

Rick

I thought the gap specified is 0.06. Is that not correct?

Correct....0.060

Right you are rick, I was thinking of a different engine.