i noticed a few days ago that if i was coasting at about 40 mph and then floored it, i would chug (miss) the second i hit 50 mph. the car would chug 3-4 times and then be fine.

car got hot the other night running the air while at idle for a while. the car then starts running really rough. i shut it off and let it cool down for a few hours and then it ran fine.

i was running errands today and at about the time it got to running temperature, it started running really rough again.

at high rpms it seems fine, but at idle seems slightly rough and seems worst ant about 2000-2200 rpms.

i scanned with vagcom and got the codes in the title for random/multiple misfire, misfire cylinder 2 and misfire cylinder 6.

my first thought is coil packs, but would it be likely that 2 would go bad at the same time?

being as it is cylinders 2 and 6, i assume that those would be seperate icms, so i am assuming that isnt the problem.

dirty maf? something else?

all ideas and suggestions appreciated. i have tried using the search function but i am getting wayyyyyyy too many possibilities

i had timing belt and all associated goodies replaced probably 2 or 3 weeks ago and it has ran fine since then, so i assume it isnt anything to do with that

my last fuel fill up was probably a week ago but cant remember if it was before i had the initial chugging problem or not so i cant rule out a bad tank of gas.

i just really dont want to have to go through replacing a ton of things to find out which was the culprit. im still thinking that the coil packs are where i should start, but dont think that it makes sense for two to go bad at the exact same time

also, dont know if it is relevant, but my battery gauge has been reading slightly lower than normal for the last week or so, and the battery is less than a year old, would an alternator have anything to do with misfire codes? maybe the new accessory belt has stretched and needs tightening? or does the tensioner automatically account for that?


should i start with cleaning the maf? replacing fuel filter and running a new tak of gas through? replacing the two suspect coil packs? replacing icm?

 

btw, i have no cel on even with the car running rough and throwing misfire codes

 

My first guess is that it has something to do with the timing belt change. I wouold retrace my steps and be sure that the belt isn't losing a tensioner and gettign too much slack in it.

 

As of the drive to work today I now have a cel that flashes from 2200-2800 rpms so I'm driving at about 3000rpms

there is also a bad smell now. The voltmeter is reading normal again.

I didn't do the timing belt and u fortunately the guy that did leaves for his 2 week trip to china this morning.

If it was the timing belt would it only be one cyl per side? Wouldn't all of them be misfiring on one side? Would it have run fine for 3 weeks after the timing belt change?

 

i now have a solid cel and a p0303 misfire cylinder 3.

its getting worse, im assuming ishould probably stop driving it.

right now im thinking the timing was slightly off when the new belt was put on and the valves are slightly being tapped by the pistons causing the problem to manifest slowly but surely?

 

Get the compression tested to be sure the cylinder is okay. Then replace the coil in that cylinder with a known good one.

 

If your pistons tapped your valves, you wouldn't have a rough idle, you would have no idle, so let's relax a bit and rule that out. Your problem is wandering around, if your diagnosis is accurate, so this means a fueling or air measurement problem. First, make sure all intake hose clamps are on nice and tight. The "then floor it" would pop a hose off for a minute, then it might settle back down and work fine for a while. Next, check all wiring connections to make sure they are fully seated, particularly the coil packs, the ICMs and the MAF. After you have done this, clear your codes, run the car some more and see if the problem reoccurs. If so, a CTS might be at fault or an A/C compressor going bad.

Let us know.

Bob

 

well, so far all the hoses for the intake look good, all electrical connections look good. the one problem i did see was a vacuum line. if you follow the ones off of the diverter valves, they hit a tee. they come out of the tee with an inch long braided fabric hose that hits a metal line. this inch long one looks like it may be leaking and there is even a pile of the dried out braided material sitting on the engine under it like it has started to just fall apart, so im going to try to replace it today.

i replaced the number 2 coil pack with a new one, and for a while that was the only cylinder showing a misfire (which baffled me), but the other ones eventually came back on. the spark plugs dont look so hot, so im going to try to replace those and then i think the next step may be the icm. any idea which one controls which cylinders? im sure that since the misfires are on both sides of the engine that i will need to replace both icms, but i keep reading that a cylinder 2 misfire is usually an icm, so im gonna try it and see what happens.

i also have a code popping now for an o2 sensor. ill post which one when i rescan it. im hoping i havent damaged it by driving with all the misfires.

i updated the cts about 4 months ago, so i dont think that is it.

i do have a bad fan control unit that needs replacing, so im hoping the heat didnt do any damage, though all this started after the one and only time the car made it over the halfway point on the temp gauge.

 

on a whim i flipped the airbox around and connected wires to the opposite icm that they were originally attached to. instantly the misfire went from cylinder 2 to cylinder 5. so the winner is.....bad icm




question is, is there another name for the icm because i cant find anything listed at the parts stores

 

Just spell it out. Ignition control module. They are everywhere.

Something curious though... What about the other misfires? Cylinder 3? Cylinder 6? that you mentioned???

I would follow the vacuum lines carefully and replace as much as possible. These old lines get so brittle. There is a good chance that the guy who did the belt may have broken a few without knowing.

FYI, most of the seasoned techs working on these warn customers that there is a good chance that some vacuum lines as well as the PCV line may be broker during the procedure, before doing the TB job.