pitks

Yes. Carbon build-up on valves is getting bigger and bigger. After some time you will get misfire with any brand or octane of gas. Try 94 gas and see if you will continue getting misfire. If no - as you mechanic to use TerraClean solution to clean valves. It did the trick for me. I'm no longer getting any misfire on any type or brand of gas.

Another reason for misfire CEL can be carbon built-up on valves. Don't use any crap from stores. Go to subaru shop and ask them to use TerraClean solution.

Code will be back if cylinder misfire again.

My CEL P0302 storry is not over. Everything is replaced - coil's, plug's, injectors, wires. Before I used to have 301 and 302. Now it is only 302. But only if I'm using 87 (89) gas. If 91-94 - no CEL. Look like I have carbon on intake valve and this is the main reason of misfire.

I'm attaching a few pages from service manual for 2004 Legacy. it is a long instruction how to fix this code

SubaruCode31.pdf

Code 31 is THROTTLE POSITION SENSOR.

Shift point too high or too low; excessive shift shock; excessive tight corner “braking”.

2003 GT does not have turbo (unfortunately), so no turbo - no vacuum.

 

Subaru Canada suspected carbon build-up on 2-nd cylinder valve, and recommended 2-3 tanks of Sunoco 94 gas. They have additive to clean valves. Let's see how it will go. If after 2-3 tanks of 94 I will have the same problem - valves need to be replaced (no cost for me, full entended warranty)

My story:

 

P0301 and P0302 on idle (760rpm) from time to time.

 

1. Replaced coil - the same codes came back

2. Replaced spark plugs wire - no difference

3. Replaced all 4 spark plugs - no difference

4. Flushed injectors - only P0302 came

5. Replaced injectors - nothing for a 1.5 week. Today - P0302 back :-(

 

What is next ????

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Legacy GT 2003 MT, 107K km.