The car always had a cold idle problem, when you rev the car in the morning and let go of the gas, it wants to die before it surges again. When i try to adjust the duty cycle, it dies. I did a tune-up on it when my parents bought it 4 years ago. Last week, i changed the plugs, wires, cap/rotor and filters, and i found two spark plugs with broken center electrodes on them, from the 4th and 5th cylinders. Now, the car runs with a rough idle. I have adjusted the timing to TDC, per emissions label when i first did the plugs, and again this time.

I have come to two conclusions:
1. i need to reseal the intake to fix the car running lean, all the vacuum connections are fine.
2. the engine is a victim of detonation.

what else could it be?

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1984 380SL-driving and service privileges.