I have searched the threads and find similar issues with some foresters. But...not exactly what I am experiencing. Let me give a rundown and see what pops up.

 

2002 Forester 4 cyl. 110,000 miles. Noticed that at 2050 and again at around 2800 rpm that there is a flat spot, bog or hesitation on mild acceleration or when cruising close to those rpms. Recently had a bad knock sensor the that tripped CEL when outside humidity was up (I live in WY where it is DRY). Had the car in to the dealer to replace front half axles (I ran out of time and had them do it cause of a ripped boot was slinging grease) Dealer read the codes also and replaced a MF sensor (?). Finally I replaced the Knock sensor then took car on long trip. CEL came on again with a P0420 code. It was about this time that I notice the subtle flat spot. Last week I decided to run some fuel line cleaner through it. Bog still there. Thinking it was the new NGK plugs I put in last fall or bad wires I examined the wires late one night and noticed no cross arcing. I pulled the plug boots and found all the tubes oily. Redid valve cover gaskets and spark plug seals. replace the plugs with new NGK Iridiums and did new plug wires. While at it, I decided to put a new air filter in and found the old one clean, but partially melted as if it had been backfiring through the intake. replace it. Still have the bog.

 

Question.....What is my next step? Front O2? Is it possible my cat is bad?

 

by the way....it is getting almost 30mpg but the plugs still show a slight rich condition.

Edited August 20, 201114 yr by gorgonc3
adding info

exactly the same symptoms before and after replacing the plugs and wires?

still have the P0420 cylinder misfire code?

what brand wires did you use?

 

cylinder misfires are usually plugs/wires. but can be other things too.

 

i'd replace the coil pack with a known good used one. but there are ways to test yours, i've just never had to test them since i've got others lying around.

 

i had a really bad cylinder misfire last year in a 2000 forester i couldn't track down, car wouldn't even run - wasn't resolved until i replaced the entire intake - so i'm only guessing that it may have been fuel injectors/FPR?