B5 A4 2.8 idle roughness/misfire? Please help!!!

[twilson9849]

I've had my a4 for a couple months now and its been pretty good but I'm starting to run into problems and could really use some help. So the deal is that the car drives perfectly fine, nice and smooth but whenever I stop at a light the rpms (about 750-800 rpm) bob up and down and the car shudders a bit. Its been throwing a CEL fora p0304 misfire on cylinder 4, but the CEL goes on and off every few days. So pretty much what I'm trying to do is narrow down possible causes so here is whats going on with it now: I'm 90% sure its got the common valve cover gasket leaks so there's that, also apparently my fuel filter is contaminated. Just yesterday i got a new upper bank o2 sensor that was going out and a tune up so i know its not the wires or spark plugs. I didn't get a new coil pack but could it be that? Or possibly low compression or a bad injector? I've been reading around and have also heard things like distributor caps, ignition control modules and different, idle air controls(or whatever), etc. So if anyone could pitch in some past experiences with this problem or some expertise it would be super appreciated, I can't affor to try a bunch of things but I can do what needs to be done at the moment.

[nemick]

This sounds exactly like a dirty or failing MAF. Change that I'll bet your issue will go away.

[Wrath And Tears]

The 2.8 coil pack is pretty cool in that if it starts failing you normally get misfires on both of the cylinders fired by one... bank? not sure what is called but the coil pack is broken up into three of them. Were the wires and plugs replaced at your tune up? I assume that's why you said to ignore them. If not thats a good place to start if they are old. Or at least pull the number 4 plug and take a look at it. If your valve cover gaskets have failed and are leaking oil into the spark plug wells that can cause misfires. Replacing your fuel filter should also be a number 1 thing to start with as well.

I would not replace the MAF as it does not sound like a MAF related issue. If it was then you would be missing on all cylinders randomly. Since it stays on number 4 its best to check that wire and spark plug before doing anything.

[twilson9849]

Yeah I got the spark plugs and wires replaced two days ago and I had the problem before and after then but yeah I think the fuel filter and valve cover gaskets will be next on my list, but does anyone think there might be anything else at all or does this sound those a safe bet?

[KingJust627]

If you all don't mind, can I contribute to this conversation some more? I myself am having an issue with cylinder 4. Misfire... but the weird thing is I can pop the hood open, pull the wire from the spark plug then plug it back in and the misfiring (rough idle) goes away. I've replace plug 4 already properly gapped. I've ohm'ed tested wire number 4 and wire number 1 to compare and the resistance is pretty much identical. It's temperamental when it wants to throw misfires then clear itself up. Just thinking back to my car knowledge, these weird actions towards the symptoms on cylinder 4 lead me to a grounding issue of some sort... but I know I maybe wrong. I can't think of anything else at the moment for the randomness to just cylinder 4 misfire. Please excuse me if there is any thought that I maybe highjacking the thread, i'm not. I'm justing adding to the conversation. If the OP feels that i'm thread jacking, I will respectfully bow out. Thanks!