my STI has gone crazy!

[beardless_viking]

a couple months ago my car started throwing a DTC P0303 which is a cylinder 3 misfire. i never noticed any type of change in performance or anything so, like a dumbass, i just pushed it off assuming that its most likely a knock sensor thats going bad. well, the other day i was driving and the CEL came on (has been coming on and off the whole time) and i noticed my car shaking much more than usual while i was going about 80 down the highway. anyway, i diddnt really think too much of it. but then i came to a stop at a light and my car started shaking violently and my CEL started flashing at me. after i started going again in 1st gear it went back to normal but the CEL stayed on like how it normally would. today i went and got it checked to see if any new codes came up. nothing. but now when ever i start to get on it the CEL will flash until i get off the gas and will return to normal. later today im going to check the spark plugs and coils and switch the number 1 and number 3 codes in hope that the code will move from the 3 cylinder to the 1 discovering that that coil is the issue. but i still have to wait to get that knock sensor. army pay periods can be a bitch. but anyway, any help is very, VERY appreciated.

 

[HolyCrapItsFast]

What year car?

Also if the problem does not follow the coil or plug, you will want to look at the injectors next and swap them out with one another. The other thing it could be is a poor connection or intermittent wire but these are rare

I doubt it has anything to do with the knock sensor. If that is bad it will throw a hard code. Generally when the CEL starts acting like this you have some major problems. If none of the above works for you then you need to get a compression test done because you know what I'm thinking right now.

Do you have an AccessPort or and OpenPort 2?

Can you monitor some parameters and take logs? What you could do here is monitor Fuel Trims, knock and Cylinder Roughness.

Does the car burn any oil?

 

[beardless_viking]

its an 06. and no the car is completely stock except for a cold air intake and a cobb bypass valve. and like i said, the car runs perfect except for that little mishap that lasted about 5 seconds. thats why im thinking its electrical rather than mechanical. but im most likely just in denial.

 

[HolyCrapItsFast]

its an 06. and no the car is completely stock except for a cold air intake and a cobb bypass valve. and like i said, the car runs perfect except for that little mishap that lasted about 5 seconds. thats why im thinking its electrical rather than mechanical. but im most likely just in denial.

Well if it does turn out for the worst I feel your pain... It looks like you are on the right track with diagnosing this... Just do one thing at a time and the process of elimination will reveal all.

Just to re-cap... Plug > coils > Injectors > Wires > Compression Test.

And if you can, monitoring or logging the Cylinder Roughness parameters is an easy way to see if you are making progress even if there is little difference in observed smoothness. The roughness parameters will show the smallest amount. :tup:

 

[beardless_viking]

thank you for the help. its greatly appreciated.

 

[beardless_viking]

well i just switched two of the ignition coils. so now instead of a hard code being thrown the cel just flashes a couple times and shuts off. i would go back to oreillys to put a code reader on it to see if the code followed the coil...but i dont feel like being crushed today. lol

 

[HolyCrapItsFast]

When you check this, your not going WOT right?

Flashing lights are not good but I only ever saw that happen when over boosting is eminant.