P0304 and P0171 in '03 Matrix

[Buckeye25]

So this is my first post here and it's not a good one... My 2003 Matrix XR AWD started to misfire about a week ago. I noticed it more during hard acceleration or low rpm's. It has gotten a lot worse within the last couple of days. It misfires/hesitates a lot more now. It is still only doing it during acceleration or low rpm's, but it runs perfectly fine after about 20 minutes of driving. I wasn't getting a CEL this whole time. I just replaced the spark plugs and that was not the problem. Today I was driving home from class and it finally threw out a CEL. It came on then would blink intermittently and then it eventually remained lit. I rushed over to Advance and these are the codes that popped up; P0304(Cylinder #4 Misfire) and P0171(System too lean). My first guess is the injector on cylinder #4, but I would like some suggestions on where I should start so I don't end up spending all of my drug money on this. Thanks!

[mikered30]

Anyway, does your car fit theses symptoms and how cold is it where you live?: http://ww2.justanswer.com/uploads/sk...rolla_0171.pdf

How many miles and when was the last time you changed the plugs? You could rotate the plugs and see if it comes back. How does your engine behave on cold start ups? Tach bouncing or steady?

[Buckeye25]

Originally Posted by mikered30

Anyway, does your car fit theses symptoms and how cold is it where you live?: http://ww2.justanswer.com/uploads/sk...rolla_0171.pdf

How many miles and when was the last time you changed the plugs? You could rotate the plugs and see if it comes back. How does your engine behave on cold start ups? Tach bouncing or steady?

It's below freezing here in Ohio and yes it has those symptoms stated in the .pdf. I changed the plugs two days ago with Bosch Platinum. It usually runs worse during cold start ups rather than warm. I don't notice the tach bouncing, but I start my car and let it warm up before I leave so I don't really pay attention to it. I will next time though. Oh, and it has 170k miles on it.

[EBR]

Have a look around the intake manifold where it meets the cylinder head. It is probably moist looking, like there is a leak.

If it looks moist, change the intake manifold gasket to the updated one. The new one is NOT black it is ORANGE.

After you change the gasket clear the codes and reset the ECM memory. Either by using the scan tool function or by pulling the EFI fuse for a minute.