Well, a bad o2 screwing up Fuel/air ratios can actually wipe out a cat, which is not something you want to pay for. Sometimes paying a mechanic for diagnostics is worthwhile, Engine misfires are difficult to nail down without something to monitor the changes you make. For instance, did changing the coil actually change anything or did the car just adjust?

You could have multiple problems, or it could just be a weak fuel pump. Clogged fuel filter (I've never seen one cause rough idle, but its possible) Bad power stage (I change a lot of these, I keep a good one at the shop just to swap out for easy diagnostics now) bad coils or a bad injector, etc. I'd also take whatever the autozone tool spit at you with a grain of salt, better to have a real scanner on it. Find an independent, don't goto the dealer.

 

Thanks again for the advice, I'm happy to get it, whether its from the same person or a bunch of different ones, thanks for your help NHolzschuh and please post as much as you'd like! I looked at that thread and what RandomAudiOwner said, along with doing some more research. Now, I'm a little worried that it might be the catalytic converter, which would suck, they sound expensive. From my reading on misfires, it sounds like if you drive around for long with a misfire, that can ruin a cat, too. Also, on that thread you linked, one post says that the P0136 code means that its the "downstream O2 sensor and that means a bad cat". My misfire first happened only a week or so ago, I drove the car as little as possible since then, although its my only transportation, so I had to drive here and there, I probably put 100 or 150 miles on it at the most since the misfire started and most of that time it was running fine, the misfire would happen here and there and then go away, it was only in the last day that it started happening all the time and I knew I had to do something right away, but I didn't drive that many miles when it was actually misfiring, could a cat get ruined that quickly, assuming it was OK before the misfiring started? I sure hope its not a bad cat, but I'm starting to wonder because before the misfiring started, the car idled just fine and now when I start it, it won't hold an idle, although the misfiring now seems to be gone and since I replaced the coil in the misfiring cylinder, it runs great other than not holding an idle.

 

well the good news is if it is the cat, you can go to a junkyard and pull one and they'll usually last you more then long enough till you can buy a new one, sometimes depending on how long the car was there you could potentially keep that cat for as long as you own the car(I've seen it happen).

now the bad news with that is its not EASY to remove nor reinstall, if you have good enough friends you could find someone to cut it from the junkyard car then spend some sweet time putting it on your car.

 

Didn't sleep too well, I was probably dreaming about the car! I got up early and did some more searching about the cat, misfires, etc. then I took it out for another short run. Same thing again, when I started it, it fired right up, stumbled a bit and died. I'm able to get it going by feathering the gas a bit and getting it into drive, then it seems to drive fine, although it died at the first stop I came to. Once it gets above idle, its real smooth, as smooth as it ever was since I've owned it, the misfire sure seems like its gone, so the new coil pack seems to be the fix for that, but I'm still trying to figure out the idle problems. I drove it for another 20 minutes or so and the CEL still hasn't come back on since I cleared it last night, but something is still definitely not right with the car.

One thing I read in another thread about a bad cat converter is that it will cause the engine to run rough at higher rpm's, which mine isn't doing, although I only saw this mentioned once, maybe that's not correct all the time. Before I cleared the codes last night, it did have both the P0422 code (Main Catalyst Below Threshold-Bank 1) and the P0136 (O2 Sensor Circuit Malfunction-Bank 1 Sensor 2), both of those codes I see popping up in a lot of threads related to possibly bad cat's.

This all again revolves around the fact that I'll be tight on cash for the next week, once I start my new job next week, everything should be fine money-wise, but for the next week, I'm on a real shoestring budget, no extra cash for buying parts or taking the car in to figure out what's up with it. I don't have to drive much, I have to make a trip today, about 40 miles round trip on the highway, but other than that I don't see having to do too much driving, my new job is 1 mile from home and I can eliminate any unnecessary trips till I can get fixed whatever needs fixing the week after.

I guess my questions now are:

-I'm still wondering if I could have ruined my cat that quickly, by driving about 100 miles total with a misfire that only happened occasionally over the last week?

-Could it still be just a bad O2 sensor, or is it a bad cat that's causing the idle problems?

-Even if the whole cat is ruined, if I do limited driving for the next week (I'm sure I could keep it under 100 miles including the 40 miles I have to drive today) and baby it as much as I can, am I risking causing any other problems with the car? Its my only transportation and I just can't spare any money this week on fixing it.

 

Did you ever look to see if the suction pump was dissconnected like the thread I showed?

 

I left to take the trip I couldn't avoid this morning (about 40 miles round trip) and everything was going ok like it did after I replaced the coil last night. It did stumble and die at the first two stops, then it was running great, nice and smooth and holding at idle when I came to a stop. I got on the highway and made it maybe 7 or 8 miles when it suddenly started running like crap, apparently misfiring again. I got off the highway right away and started taking side roads back to the house so as not to stress the motor too much. The CEL came on soon after and soon after it came on, it started flashing. It stopped flashing after a couple of minutes but stayed on then. As I was driving back, it started running smooth again for a while, then went back to misfiring again. The CEL stayed on and flashed again for a minute or two, then went back to solid on.

The auto parts store is right by my house, so I stopped there and got the scanner again. This time, it only showed 2 codes:

P1300-something about fuel system dealing with misfires?

P0303-cylinder 3 misfire

So, cylinder 3 is the same one as was on the misfire code last night before I cleared the codes. I replaced the coil pack in #3, so that shouldn't be it, unless by some small chance I got a bad coil out of the box. I did find one thread on another forum that mentioned that if you have P1300 and P0303 in combination, that its a clogged fuel injector and that you should clean the injector and change the fuel filter-could this have something to do with it? It just seems weird to me that the problems come and go, the car will run real smooth for a while and then start misfiring again, then go back to running smooth, back to misfiring, etc. etc.

Pbrules10-I forgot to check the suction pump like you mentioned, I'll go out and check it right after this, thanks!

If it would be a clogged injector, how would I remedy that-would it be as easy as running some injector cleaner through my gas tank, or is it more involved than that? Heck, that might be a good thing, then I could take the new coil pack back and get my $60 back!

 

The rough idle can easily be a vacuum leak, And the misfire can easily be a bad injector. With the AZ scanner you can easily swap injectors between cyl. 3 and another one, head back to AZ and rescan. If the miss moves, then it's the injector. You can do the same with coils, but you replaced that one so i'd focus on different causes.

 

PBRules10-now I can't find what you are talking about, I thought I saw it earlier, maybe I'm going nuts.

Now I'm going to take a look at swapping the injectors and going back to AutoZone and rescanning like randomAudiGuy mentioned. I'll be back!

 

Take a look at the picture in my thread again. Try finding it, it could be the problem! I went crazy for a long time trying to find the problem. Turned out to be a little piece of disconnected plastic.

 

60.00 for 1 coil pack? my local autozone has them for only 23.00 each!