Hello, I have a 1990 Cadillac Deville with the 4.5L V8 with 85K miles. It's have a rough idle as well as a shake felt through the steering wheel and gas pedal when under light load. If I stomp / chop on the gas, it smoothes out. When coasting, there's no shake. A mechanic told me that cyl#3 is misfiring. He went through the spark plugs, wires, and dist cap and had confidence that it wasn't an electrical issue. If I pull the plug wire off of cyl#3 at idle, it runs rougher, so she's firing, but maybe not always.Can the injectors have these issues of intermittent missing under different load ranges?
JA: How often does the vibration occur, and when did you last have the tires balanced?
Customer: Under light load only. It goes away if I power through it. I'm pretty sure that it's not unbalanced tires. It's dead-smooth while coasting. It will shake at any speed. It's only dependent on the engine
rpm's and load.
JA: Are you fixing your DeVille yourself? What have you tried so far?
Customer: Mostly myself. I took it in to have the mechanic to look everything over (just bought it) and he told me to run Chevron Techron injector cleaner through it, only to make the issue a little worse. I've also replaced the in line fuel filter
with no change and he had changed the plugs.
JA: Anything else you want the mechanic to know before I connect you?
Customer: If I'm cruising at 70mph, it gives me a rhythmic shake about every couple of second it shakes for about half a second, smoothes out, and shakes again, mile after mile.