I purchased a 2000 Forrester about 4 months ago. On inspection I found the car was running very lean. Changed the Air Filter and Fuel Filter and that corrected it. Tried an engine cleaner gas additive and immediately got the CEL code for bad Air Fuel Mix Sensor (O2#1) and fixed that about 1 month ago. I was getting 30 mpg on the lean mix and now I am down to 20mpg with things fixed. The car seemed to be running extra rich and wanted to bog down at low rpm shifting.

 

It is a Manual with the Horizontally Opposed 4 Cyl. NOT turbo.

 

In the last couple weeks the car has developed a problem with acceleration. When I go easy gas (less than 10% pedal) and high RPM (over 2500) the engine runs fine. When I attempt to give her some gas or dare try to punch it to the floor, I get caughing, slowdown and even backfiring instead of a thrilling speed increase.

 

So now I have to be very careful to accelerate with just the right pressure on the gas pedal to make the minimum on the gas and keep higher rpm to keep from backfiring. I am hoping this is plugs and wires or something simple, I am dreading the internal timing chain or something serious. Please help.

Replace the plugs, plug wires and the fuel filter. They need it anyway so if that doesn't do it you've eliminated a few things.

I'd also do a check of the vacuum lines, a split hose at one end or the other makes for mysterious symptoms.

Thanks for the tip. I have already done the Fuel Filter within 3 months. I just bought spark plugs and will report on changes.

 

It seems like it is flooding and missing when I stomp on it. Also starting to get rough starting. Might be a battery on that side, but maybe not getting enough spark to start quick?

On replacing the plugs, these are the strangest plug wire ends I have ever seen, I am used to the traditional american wire ends. Do I just pull them off (with appropriate care of course)? Also, do you recommend removing the battery and washer fluid reservoir to get to the driver's side plugs?

Followed the instructions on general maintenance. Took out the air system and wiper fluid tank and swapped out the plugs. It was a very simple job, just needed to get a bit of wether warmer than single digits. Took about 45 mins.

 

The Forrester runs AWESOME now. Seems as though the plugs were the latest and hopefully last step for a while in neglected routine maintenance by the previous owner.

 

Thanks for the help. Case Closed.

One final note. Following the spark plug swap, I was still getting a bad #2 cyl C.E.L. So, I pulled the Bosch plugs and used the OEM import plugs and changed the plug wires and now the engine is running better.