'94 bonneville 106k miles.

Starting a month ago car began to run rough on the road and I figured it was because I took it to walmart and they poorly balanced the tires. Problem quickly got worse and began to lurch and the back end feels like it drags, especially when accelerating or cruising at higher speeds (50+). Problem is considerably worse in overdrive. The lurching and rumbling can be temporarily alleviated by the feathering the gas a bit, but returns shortly.

When sitting at stoplights the volt gage sometimes jumps a bit and then drops to around 9-10 volts until you starting driving again.

RPM seems to run stable. Runs smooth enough in park but with a distinct, rhythmic "clacking" sound.

Gas mileage has also dropped about 12%.

No check-engine light.

Recently replaced (6 months or less): MAF sensor, serp belt, alt, fuel pump, starter, plugs + wires. None of these but the plugs were replaced in relation to this current situation.


I'm leaning toward valve or injector issue. Weather hasn't permitted much work on it in the last 2 days. Thanks for any feedback.

you look at the coil terminals while off? put dielectric grease on the terminals?

Kinda makes me wonder if you have a restriction in the exhaust, like a partially plugged cat or something like that.

None of the spark plug terminals looked bad (no cracks or carbon). 2 of them had a tiny bit more of build up on the ground electrode but nothing alarming. One did have what appeared to be almost a melted appearance to the insulating tip around the center electrode. Looked kind of bubbled and melted is about the best I can describe it. Wish I recalled which one it was...I think it was 5. I was a bit distracted with my wife "helping."

I put dielectric grease around the inside of the boot and the ceramic insulator - it doesn't belong on the terminals. Car still ran the same way after replacing the plugs.

Gonna head out there with a screwdriver this afternoon and listen to the injectors.

spray the coils with water while running it may be leaking voltage to the center screw. the dielectric strength of the plastic on the coil can break down as mush as the wires. if the engine stumbles or you see arcs theres your issue