Hello scotty , I have a 2011 Toyota corolla with 280000 miles on it and I'm spending a fortune replacing my ignition coils. I've had one go bad a year ago , so after having It replaced , I decided to have the rest of them replaced with denso oem coils to prevent this from happening again. Low and behold I've Had to replace the cylinder 4 coil twice since then. The car tends to vibrate and the idle fluctuates when at a stop.What is going on here ?
It sounds like it's only one ignition coil that's giving you a problem.
The cylinder #4 ignition coil.
It doesn't matter if you have an old 1960's pickup truck with a single coil and a distributor or a modern car with coil on plug ignition coils (COP coils), what kills ignition coils is an "open" or a short to ground on the secondary side of the ignition coil circuit.
In the case of a COP coil, it's unlikely to have an "open" in the secondary side of the circuit because there aren't any spark plug wires. And indeed if there were an open in the coil component itself, you'd remedy that by replacing the COP coil.
But your problem persists even after replacing the COP coil.
So, what about a short to ground on the secondary side?
Something like carbon tracking on the spark plug insulator. Or, considering the mileage of your engine, worn piston rings allowing oil into the combustion chamber. Or maybe a tiny head gasket leak allowing coolant into the combustion chamber.
Anything that would allow the spark to short to ground from the spark plug center electrode instead of forcing the spark to jump the gap from the center electrode to the ground electrode.
So inspect that spark plug. Do it in the morning. Is there carbon tracking on the insulator? Is it wet from a possible tiny head gasket leak? Is it oily? Is it crudded up with carbon?
Maybe do a compression test and a leakdown test on cylinder #4
Perhaps more details will result in better help
