So I am picking up a Forester on Saturday. I was told its been running on 3 cylinders for the last couple months but doesn't overheat or anything else. Would it be smart to start with a new coil pack and plugs and wires.

I haven't seen many Coil Packs fail on these so it's probably a wire or plug. Start with pulling the spark plug wire for each cylinder while the engine is running. If the engine speed changes move on to the next and do that with each cylinder until you don't notice the engine speed change. Thats your problem cylinder. Hold that wire close to a grounded metal part on your vehicle and see if your spark jumps. If it does jump then its your spark plug or your injector. If it doesnt jump then remove the spark plug wire for that cylinder from your coil pack and hold it as close to that now open port on your coil and see if the spark jumps. If it doesn't then it's you pack, if it does then it's your plug wire.
If your wire checks out try removing the injector wire and plug it back in and wiggle it to see if that helps it. If it doesn't, pull your plug to make sure it isn't gummed up. If it's not , make sure you have compression in that cylinder. If so move to the injector.  My guess is its your wire. Although on my 99 I recently had a cylinder missing. Turns out my power steering pump was leaking and the fluid was pooling in my spark plug hole and the spark was grounding thru that. Good Luck.

Find out which cylinder is not running/improperly. There will be a code. If no 4, the biggest possibility is a burnt exhaust valve. This will require a head job.

If you can do the work yourself, then it's not fatal. If you have to pay someone, then it would be a deal breaker.

 

O.

Thanks for the info. If it's a bad valve, I will swap it to a 2.2. I'm only paying $400 for the car. It's in pretty good shape otherwise with 199k on it.

So I got the car and no cel. I pulled each plug from the coil one at a time and all made a difference in idle. Am I most likely looking at a bad valve

Suggest you pull the plugs. Who knows, maybe just a bad plug causing the miss.

 

Suggest you change the oil and filter, as prolly oil diluted with gasoline from the "miss."

try plug, wire, coil and fuel injector. (switch injectors and see if the miss follows it)

 

As mentioned, 98 is the golden year for a forester since you can put a 90-98 2.2 bullet proof motor in there.

Burned valve would cause a dead miss at idle.

Most likely just has an intermittent/occasional misfire. Plug and wires.