HelloCustomer Let's start by gathering data and we can narrow it down. Since we have so many thoughts, let's start with the basics. Remove all 4 spark plugs and lets perform a compression test. disable ignition. Install the compression guage and crank the car. Allow 5 cycles then take a reading. The needle should hop 5 times. Make sure all 4 cylinders are measured the same way. You should see 125-150 psi on each cylinder. Whatever the reading is, all cylinders should be very close to each other. If you find compression readings varying greatly from cylinder to cylinder, suspect a timing chain/belt issue. Let me know what you find.
Your JA Expert,
Stan, I am going to presume your car is Canadian. In your first post, you indicated a LeMans, The last Lemans we had in the US was a 4 cyl. If your car is Canadian, I'm sure we have an equivalent model here. What displacement is your engine and is it a 4 or 2 door car. I want to figure out which vehicle platform it is, so I can rethink my approach. Same test applies for compression testing, However do all 8 cylinders. Same deal. Erratic compression readings confirm a timing chain issue. By any chance is your engine a 5.7 Lt1 style engine?
6 cylinders sound more like it, now we can be assured we are talking about the same car. Stan let me know if you need any help, second opinions, anything. I'm here for you. Have a great night, and I'll keep my fingers crossed that it's something minor.