00 SW2 Running rough
 

Occasionally my 2000 SW2 will run rough, like it's only firing on 3 cylinders. It happens randomly but only when warmed up and usually when my wife is driving it. It finally got to doing it enough that it's done it for me twice now.
The first time it ran like that for about 15 minutes of the 45 minute drive home from work. Didn't seem to matter what I did behind the wheel it didn't get any better until I got on the twisties 10 minutes before getting home and then it started running right over the course of a 1/2 mile.
Couldn't find my code reader that night but today it did it again and at times it seemed like it was running on only two cylinders. The good part is it did it all the way home and I was able to get the code reader hooked up while it was misbehaving.
Initial code set:
P0133
P0404
P0405
P0420
P0731
Cleared the codes and after several minutes of chup-chup-chup idling it set the following code:
P0302.
I looked them up and it appears to be the EGR, Cyl 2 misfire and CAT codes (along with the usual tranny code for an unfixed problem there).
Great! I pulled the EGR valve and it did seem to be sticking and need cleaning so I cleaned it up and got it working smoothly again.
Before I put it back on I looked at the ports where it mounts and they looked unbelievably good. I thought for sure they would be all carboned up and stuff but besides a very thin coating of carbon they were wide open.
So, I put the valve back on, re-attached the connector (which looked to be in excellent condition by the way) and cranked it back up.
chup-chup-chup....
Ok, maybe the plug's a little fouled from not firing for a while. Ran the car for a few minutes, revved it up a few times (no, not redline) and no change.
Maybe I'm being a little impatient and it'll clear up if I give it more time but for now I'm ready to pull plugs and see what I can see.
Not going to happen tonight but that's the plan.

Anyone have any thoughts, experiences that might relate and could help?

P0404 EGR open performance
P0405 EGR circuit low
P0420 Catalyst below efficiency threshold
P0302 Cylinder 2 misfire
P0133 Heated Oxygen sensor slow response bank 1 sensor 1
P0731 Gear 1 incorrect ratio
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Your EGR cleaning was definitely a good first step. It's not at all uncommon to clean an s car EGR, put it back on and have the car run like poopy. If it's so gummed up that movement is impeded, you're dislodging a bunch of crud and sometimes little shards lodge where you can't see them.

Pull the EGR and clean again. I fill it up w carb/choke cleaner, let it soak for 30 min, then pour out, refill, work the pintle to free it up, pour out, and rinse w carb choke cleaner with the straw that comes with the bottle attached to focus a high pressure stream. Rinse it at least 3 times as long as you think you should. Check pintle movement and reattach.

If you still get p0404 and P0405 it may be an issue with the EGR position sensor itself or possibly the EGR solenoid. Check the EGR fuse. Could also be an issue w current not getting to the EGR solenoid to actuate it or no voltage current at the EGR , meaning nothing is happening when the solenoid is actuated.
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Sounds like you are tracking down the cyl 2 misfire.

The P0133 is the front O2 responding too slowly, meaning the feedback to the ECM regarding air fuel mix is wrong as a function of time. You may be running at times way too rich and at times way too lean. All depends on how slow and how reduced the sensor's output range is. Point is, this is very likely contributing to the poor performance. Also, if you are running super rich you may actually be dumping raw gas into the catcon which accelerates its death.
P0420 may be a false code triggered by the front 02. Won't know until you replace the front 02.
P0731 gear 1 incorrect ratio -- if 1st gear is not problematic, may be a solenoid in the valve body gunked up or going bad. I'm not a tranny guy by a longshot, but most problems w the TAAT transmissions in the s cars are with the valve body solenoids and the input shaft nut. Internal failures do happen, but hold back on chasing them down until you've checked the other possibilities.

I'm going to see if I can round up some plugs today and replace what's there. Last tune up was about 4 years ago so eh.. could use 'em.
Derf, I'll pull that EGR again and give it a couple more cleanings just to be sure although it was moving easily after I cleaned it yesterday. I used a combination of Gumout carb cleaner soak, using the straw to blast it out both ways and using compressed air (from a can) and it's straw to blow it out both ways. I'll put a meter on the valve and the connector to see what I can see this time too. If I can find out what the wiring is on the valve I might bench test it too.

There's also a possibility I have a coil going bad and I'll be checking that too.

Oil consumption is high, at least a quart every tank of gas. I've been getting complaints from the ECM about the CAT for some time now and it's on my to do list to replace it and the O2 sensors but it's been running well otherwise for now (excepting of course this occasional misfire situation). Most every car I've owned has been an oil burner or leaked or both so I've become quite used to it to the point I probably don't give it enough consideration. Oil's cheap compared to car payments so I tend to not worry about it as long as it's running well and get's me where I'm going.
It could be though that it's getting bad enough for long enough now that it's fouled a plug in addition to messing with the CAT and the O2 sensors. I'll see when I pull the plugs today.

Plugs indeed. Figured you had already pulled. Use the stock NGK plugs. Copper, .040 . Anything else and you are asking for totally avoidable problems. Might want to throw in a compression check while pulling all the plugs before dumping money into the vehicle.

If this repeat cleaning does not get rid of the EGR codes, it is either not getting voltage/ current, it is a solenoid issue, or the EGR position sensor is defective, in which case you must replace the entire EGR valve since the position sensor is built in.

All of that oil will indeed poison both the oxygen sensors. And it will trash your cat con. Go for the front sensor first of course. Then the rear. Then try to get ahold of a scan tool that records real-time data and see what the voltage levels are in real time for the oxygen sensors. That way you can determine if the cat is doing anything at all.

Use the denso labeled equivalents of the GM oxygen sensors. The OEM GM sensors are actually denso sensors anyway. The denso labeled ones are about 25% less cost wise and are identical. Again, using anything else may cause totally avoidable problems. If you choose not to, at least stay away from the bosch sensors.

definitely needed plugs. Couldn't get the NGKs locally so I grabbed some AC Delco just to get going again. Figured I'll order the NGKs from Rock Auto & swap 'em out when they get here.

https://cimg5.ibsrv.net/gimg/www.sat...d72f45f63a.jpg
bad plugs

Hey look at that! ACDelco plugs. I'll bet they were out of the NGKs last time too and just like this time I planned to replace them only to forget.

Yeah, forgetting seems to be a thing here because after I installed the fresh plugs and started it up I heard a noise that shouldn't be there. Sounded like a lifter tapping. Checked the oil and there was none on the stick. After all of 5 seconds wondering how that could be I finally remembered that the last time I gassed up it was a quart low but I didn't have any extra oil in the car so I just drove the 10 miles home where I had a case of it.
Completely forgot about it. Great.

Put two quarts in and it sounds a little better but still has a dead cylinder. Here's hoping it's just a collapsed lifter that needs some extended gentle driving to get it working again. We'll see tomorrow.

I really hate how the memory starts to get flakey as one gets older!

After this morning's drive it looks like it's permanent damage. Still got lots of power considering but it's most likely a cam lobe got wiped. I think I'm going to start keeping a pack of sticky notes and a pencil in all the vehicles. Looks like it would be well worth the investment.

Still driving it
 

Due to the usual circumstances I'm forced (well not really "forced") to continue to drive this poor car as is. I can tell by the fluctuating speed of the starter motor when I crank it that I have little to no compression in one cylinder. Not the first time I've had to drive a car like this (oh, the memories) and while I expect it to trash my already marginal CAT it should be able to go for awhile as long as I don't thrash it.
Unless the timing chain breaks.

I bought this car with 110k miles and it passed the 200k mile mark a while back. I've never replaced the timing chain and even if the previous owner replaced it right before they sold it (I don't know) it still has over 100k miles on it. Now that I've damaged the engine from lack of oil I've thinking about that chain.

The s chains have proven quite robust.
Search on s car timing chain failures on the site. You'll find very few.

Even on low oil cars.

I searched as you suggested and you're right, I can't hardly find any threads here on broken S car timing chains. I searched some other forums and found a thread where someone went to replace their timing chain as PM and discovered that the sprockets were missing teeth (20 missing on one sprocket alone) and the chain had worn a groove into the metal of the sprockets but the engine had not been making any timing chain noises or having any running problems. That definitely counts as being robust!

Knowing that takes a little of the edge off of driving this thing. Of course something else can always go wrong but for now it seems it's just a malfunction in the valve train for the #2 cylinder.
I'm just a little extra stessed right now because our 2nd vehicle is having tranny issues again that left my wife stranded in the middle of the road for a few minutes until she could get the electronics to reset again.

The local Pick-n-Save is going to have a 50% off sale this coming Saturday. I think I'm just going to pick up a whole engine for half price @ $93. I can swap it out and rebuild the old one at my leisure.