150K miles, dual exhaust, cold air intake. Coolant flushed last year but looks muddy already since before I got it it went 5 years on a change. Ok so. This only happens when it’s hot out like it’s starting to get. Whenever I’m at idle (~750 rpm) and the fan kicks on it drops to about 500 and shakes for a second then comes back up. Surges slightly when the fan kicks off. It’s not bad, I just don’t want this to progress into stalling. It doesn’t have a cooling problem. I know I need a new coil pack/plugs/wires, could this be the problem? Too much energy getting diverted from the aging ignition system when the fan comes online? Help would be greatly appreciated!