2004 Forester- Rough idling with cold start

Hi. I am posting about our 2004 Forester with 118,000 miles It has been a fairly decent car for us except for this most recent problem that 3 mechanics (including 2 Subaru dealerships) have been unable to fix. The problem is this. When there is moisture in the air (humidity, rain) the car has a very rough cold start (sitting for 12+ hours). It will either attempt to turn over and not start or it will start but then stall when put into reverse/drive. If the car does start and I let it warm up for 5 minutes it will not stall going into reverse/drive and drives perfectly fine. If the car does not start on the 1st attempt it will start on a 2nd attempt about 15 minutes later. It does not happen with a warm start, and again it only happens when there is moisture in the air.

Other than this issue the car runs fine- no complaints. So right now it just stands as a minor inconvenience in that when there is moisture in the air you have to 1). let the care idle for 5 minutes before putting into reverse/drive if it DOES start or 2). wait for 15 minutes to retry starting if it DOES NOT start.

The mechanics have tested the fuel supply (no issue) and the computer shows no error. Since this problem is sporadic it has been hard to duplicate at the shop and the Subaru mechanics have stated that they have not seen/heard of this particular issue before.

Any guesses or similar experiences with this problem. We really would like to keep this as a family car for a while more, but would like it to be more dependable.


Why would they check the fuel supply? You have something electrical being affected by the moisture in the air. Ok - well, checking fuel pressure is never a bad idea anyway, but this is a textbook ignition problem. My guess is that no one (so far) wants to be bothered.

How old are you spark plugs and wires? Do you know which engine it has?

Skip the dealerships. Too often they do nothing without error codes. It’s almost like no one knows anything anymore and needs a computer to tell them. What was the other shop you went to ? A national “auto care” chain shop perhaps? Ask around for a local hole-in-the-wall shop like “bob’s auto repair.” These problems are really not all that difficult to figure out (in comparison to other intermittent problems that produce no error codes).

If you know your way around under the hood at all you can probably find out yourself. You just need a spray bottle with some water in it, and maybe a plastic bag. On a dry-ish day when the car is having no issues you run it and simulate moisture with the spray bottle. You can use the plastic bag to isolate parts that are close together to pinpoint things. Start with the spark plug wires and ignition coil(s). Find the cam and crank sensors and mist those too.

Thanks for your input and suggestions The spark plugs are 5+ years old. The engine is XS 2.5liter H-4 165hp. I do agree that the dealerships seem unwilling/unable to do anything without an error code. I do have a local place that we will be trying out next week.

Could be a cracked coil, more than likely bad wires.