'99 Forester with misfire issues

[1197sts]

My son has a 99 Forester I am working on, it is new to us. It had the CEL on when he bought it, the codes were for #3 and #4 misfire. I took out the plugs and examined them, checked the gaps and they looked fine. I also put on a used coil pack and plug wires and cleared the codes.  After a few hundred miles the codes come back, and there seems to be a rough idle particularly when it's first started. Other than the occasional rough idle it seems to run fine.

BTW, this has the EJ253, I am mostly familiar with the EJ251, I don't know how much difference that makes.

[1 Lucky Texan]

good call on the coil think, surprised that wasn't it. plugs NGK right? how are the wires? will they swap front to back to test?

OEM plug wires preferred if you swap those.

hope it isn't a valve issue.....

[1197sts]

I found a bad vacuum line, I think it goes to the pressure regulator. So far so good, see how it goes. Sometimes it only acts up on a cold start.

1 Lucky Texan, thanks for the input. I threw used coil wires in just to see what it would do, I agree OEM wires are good, and I have had good luck with NGK as well. My thinking is, if I put in a different coil and wire set even if its used its unlikely I would get misfire on the same two cylinders.

The plugs are NGK I think they're iridium, with the pointed electrode. They measured .036 pretty close to the same on all, and they weren't too fouled or anything like that. Similar to the wires, the combination of #3 and #4 misfire seems to not be random.

I agree, lets hope the valves are good. Also, a while back the previous owner had the timing belt replaced, it could be out of time, but once the idle smooths out it runs good so kind of unlikely.

[1 Lucky Texan]

no oil on the plugs or plug wire boots?

consider scanning ecu for pending codes.

Edited July 10, 2020 by 1 Lucky Texan