OK, I searched and found some ideas, but no luck yet. And this seems so specific, thought maybe the description would trigger someone to nail the problem. So this is long...

Some weeks ago I was messing with the air intake and broke the little breather hose. So I DIY a hose and tape temporarily and had no problems.

Took car in to dealer for regular maintenance - they did coolant and brake fluid change. They also ID'd a leak in the rear main engine seal and a PS leak, but told them to hold off on that for now. They drove the car back to me (abt 100 mi of interstate) and dropped it off.

A few hours later, I took the car across town, and it began idling rough at stoplights. Made the car shake a bit, the gauge lights would dim when it chugged, it seemed to get worse the longer I sat at the lights. When accelerating, it would clear up and run normally. This happened several times. Eventually it got rough enough to kick off an amber "engine fault" light, CEL, and "reduced performance".

Hooked up to code reader and got these
P0302 - cylinder 2 misfire detected
P1313 - misfire rate catalyst damage fault - Bank 1
P1316 - misfire rate exceeds emissions

Based on some searches here, seemed like a leaky breather or intake might be the problem, so replaced both with new. No change, same symptoms.

So I am looking for other suggestions on what it could be. I am hoping maybe the dealer tech forgot to connect something, or some other problem similarly simple I could fix.

Another detail I have not mentioned: it smooths out when you give it some gas and/or get it up to speed, although the rough idle does return slightly when going up hills at speed.

Any ideas or suggestions? I've never had any other engine issues in 5 years I have owned the car. I'm also going to talk to the dealer about it, too, both looking for a quick fix and getting in their shorts in case they need to do something serious to make it right.

Thanks in advance to the brain trust here.

 

I don't know were in the order of trouble shooting this comes into play...but I'll just point out that when the coil packs have been through thousands of heat cycles they begin to breakdown and are a common cause of intermitant mis-fires....

 

I'd go along with Jazz Cat, the easiest thing to do would be do swap the coil/spark plug to another cylinder, run the car and recheck the DTCs, if the P030x coincides with the new position then you have found the problem.

 

Well, I swapped the #1 and #2 coils, and took it for a drive.

At first, it did have have the same rough idle problem, and got bad enough to trigger the amber light, reduced performance, and engine fault lights. So I was just waiting to read the codes to see if it was now #1 that was the problem.

But as I headed home, the rough idle went away. Gave it several chances by stopping in middle of roads (rural area) and waiting, but no problems at all. As if it cured itself.

So now IDK what to think. But I am not going to look a gift horse in the mouth. I will see how it responds over a week or so and post an update. Maybe it just got some bad gas, and it is working its way through.

 

Sounds like a coil/plug combination, bad plug in #2 with a weak coil.
Change to a strong coil and it burns the crud off.
I can't see your mileage but new plugs might be in order.

 

I had the same problem with my 99. I connected to an analyzer and it read # 3 cylinder misfire i swapped coil #3 to cylinder #2 hooked it up again and got a #2 misfire 60 bucks at parts geek.com for a beck arnley coil and i was running brand new

 

Did they spill some coolant that ended up down a spark plug hole when they changed it ? It only takes a small amount to cause a misfire when the plug / coil contact gets wet. The covers are not water tight so if they spilt a bit it could run along the top of the cover and seep in.

 

Well, took it for another drive and had worse problems than ever. Now had codes with misfire in #1 (as expected/hoped) and #8 (not encouraging).

I ordered 4 new ignition coils from partsgeek, and installed them. I replaced #1 and #8, and saw that 6 and 7 were pretty rusty looking, much worse than the others. So pulled those 2, but will keep just in case. When replacing #8, there did look to be some coolant down there! Good call spuddyo. Mucked out as much as possible with a paper towel.

As an aside, all the holes had a little burned up looking oil in them, just cruddy residue, not enough to pool. Except #2 which had a little, and #8 as described above. I have bought new coil covers, since some savage broke the connection grommets by torqueing them down with an air hammer apparently. And found several of the retainers have come out of their holes, so JBWeld time on those this weekend.

So put in all the coils, and started up. Immediate "gearbox fault" and code for TCM won't talk to CAN. Oh crap. Did I bump a wire? Something else. Searched threads for help. Someone mentioned battery issues...

So I checked my battery. 10V. Jeez. Got new battery. Put it in, and ALL is now well. Car runs fine, no codes, no misfires. Nice kitty.

I tested the voltage on the new battery - 10V !?! My multimeter must be miscalibrated. So maybe I didn't need a new battery, and I just needed to reset everything - I had not disconnected it when I changed the coils, maybe that was dumb.

My guess is that I had at least 1 iffy coil, the coolant in #8 making that one iffy, and an iffy battery. Add it all up to problems. And the gearbox thing was probably just from not disconnecting the battery, and solved when it was disconnected. So I probably bought more coils than needed and maybe a battery that I didn't need, but the battery was 5 years old, so sooner or later I would have had to do it anyway.

Anyway, drove it to work and back yesterday, and she is as good as ever. Hopefully that is the end of this issue. Thanks to all for help, and hope this will help someone in future.