P0303 Misfire rough idle [Archive] - GrandAmGT.com Forum


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08-24-2012, 08:18 AM
2003 V6 Grand Am with 183k miles

So a few months ago I replaced the LIM (pain in the A$$). And after multiple little issues that I was able to figure out ( coolant hose busting, vacuum leaks, etc) the car seemed to run ok for the most part but now I have a P0303 code. Which is misfire on cylinder 3. I checked the wires and other easy stuff everything seemed ok.
The symptoms are that it seems to go off for a day (usually cool) and then come back on in the afternoon (usually hot). It will idle a little rough when in neutral and rougher when in gear. Power does not seem to reduced.

I am thinking it is a fuel injector (maybe some dirt got on it during the LIM install). Any other issues you guys can think of?

One little detail that may or may not matter. During the LIM install I busted a bolt and had to use an extractor to get it out (threads were safe). But one of the extractors fell into a hole along the cam shaft (those who have done a LIM repair know where I mean). I have no idea where those holes actually go and no diagram shows where it goes. I am hoping is fell all the way to the oil pan but I don't feel like removing it to see.

08-24-2012, 01:23 PM
the very first thing i would do is change your plugs. and dont get bosch becuase those have been known to cause missfires in the 3.4l. also i would change your wires as well. personally i like to start cheap and easy and work my way down the list

if that doesnt work injectors might be the next best option. though i would try some seafoam before i went down that road

08-27-2012, 07:20 AM
The plugs and wires are no more than 8 months old. I was replacing everything for a P0420 when I got to the LIM install.

I don't think it is the plug and wires. I have gone through and checked the wires and connections. Like I said it seems to be weather related. Hot causes it to fire while cooler (<80) seems to have the light go out.

08-27-2012, 07:42 AM
Here's the recommended list of things to check for a P0303 code... http://www.obd-codes.com/p0303