Rough idle + CEL under hard acceleration
Thread Starter
Newbie
Joined: Apr 2024
Posts: 12
Likes: 0
From: Wisconsin
2008 CL65 AMG
Rough idle + CEL under hard acceleration
My 2008 CL65 has been having a rough idle and gets a CEL under hard acceleration. It also seems to be down on power a bit.
I took it to an indi shop and got the following stored codes:
20E1 - charge air coolant circuit, air temperature too high
200B - Right side CAT converter is insufficient
20A3 - Left side CAT converter is insufficient
2043 - multiple misfires
2047 - #6 cylinder misfire
Spark plugs were changed in 2020 at 60k miles and the car currently has around 83k miles.
Any thoughts on what could be causing these codes / rough idle (kind of feels like it's constantly misfiring)?
I took it to an indi shop and got the following stored codes:
20E1 - charge air coolant circuit, air temperature too high
200B - Right side CAT converter is insufficient
20A3 - Left side CAT converter is insufficient
2043 - multiple misfires
2047 - #6 cylinder misfire
Spark plugs were changed in 2020 at 60k miles and the car currently has around 83k miles.
Any thoughts on what could be causing these codes / rough idle (kind of feels like it's constantly misfiring)?
Member
Joined: May 2020
Posts: 247
Likes: 58
From: Fort Worth
2005 CL55 AMG || 2005 CL65 AMG || 1989 560SEC
I got multiple misfire codes and a charge coolant temp error when I forgot to reconnect my new intercooler pump. My working theory is the high air intake temp was causing predetonation (iirc the temps were over 200F). plugged my pump in, cleared codes, no more misfire. So, I'd guess your intercooler pump has a problem, or you have air in the system. Fix that first, then clear codes and see what still sticks.
Cat codes may just be bad o2 sensors, they do go out of spec over time.
I had a single cylinder misfire that became more frequent over time (especially under hard accel), and I had to replace a coil pack.
Good luck, have fun!
**also, if the misfire goes away on restart and comes back after hard accel, that's what mine did when the coil pack was going out. The coil packs tend to die more on a time basis than a mileage basis from what I've read- the epoxy/insulating material in the coil begins to crack, leading to shorts or resistance changes that burn out the pack. I've seen estimates of 7-10 years before coil packs have issues.
The constant misfire is the coil pack deactivating the #6 cylinder spark plugs. It's not a misfire, but zero fire.
If your valve covers are leaking, replace those while you have the coil pack replaced. they'll leak oil into the spark plug well then up into the coil packs, given enough time.
Cat codes may just be bad o2 sensors, they do go out of spec over time.
I had a single cylinder misfire that became more frequent over time (especially under hard accel), and I had to replace a coil pack.
Good luck, have fun!
**also, if the misfire goes away on restart and comes back after hard accel, that's what mine did when the coil pack was going out. The coil packs tend to die more on a time basis than a mileage basis from what I've read- the epoxy/insulating material in the coil begins to crack, leading to shorts or resistance changes that burn out the pack. I've seen estimates of 7-10 years before coil packs have issues.
The constant misfire is the coil pack deactivating the #6 cylinder spark plugs. It's not a misfire, but zero fire.
If your valve covers are leaking, replace those while you have the coil pack replaced. they'll leak oil into the spark plug well then up into the coil packs, given enough time.
Last edited by JustTXn; Jun 2, 2025 at 12:05 PM.
Super Member
Joined: May 2021
Posts: 554
Likes: 150
From: Netherlands
CL 600 '00 5.8L V12
How did the indie scan the car? Using proper Mercedes diagnostics, or using a generic ODB reader?
The car disables certain cylinders if it sees (through O2 sensors) that they are not combusting properly, however, if you're O2 sensor is faulty, it could disable cylinders whilst it shouldn't. The disablement of the cylinders end up as misfire codes on generic ODB scanners, but only show up as disabled to protect cats on Mercedes scanners.
I'd scan the car with a SDS setup and go from there.
If the car was already scanned using SDS, you might want to try and properly diagnose the O2 sensors. If those come out fine, check red sparkplug isolators, you can try the rental program at https://www.v12icpack.com/ to see if the coil pack or voltage transformer is starting to fail
The car disables certain cylinders if it sees (through O2 sensors) that they are not combusting properly, however, if you're O2 sensor is faulty, it could disable cylinders whilst it shouldn't. The disablement of the cylinders end up as misfire codes on generic ODB scanners, but only show up as disabled to protect cats on Mercedes scanners.
I'd scan the car with a SDS setup and go from there.
If the car was already scanned using SDS, you might want to try and properly diagnose the O2 sensors. If those come out fine, check red sparkplug isolators, you can try the rental program at https://www.v12icpack.com/ to see if the coil pack or voltage transformer is starting to fail
Thread Starter
Newbie
Joined: Apr 2024
Posts: 12
Likes: 0
From: Wisconsin
2008 CL65 AMG
How did the indie scan the car? Using proper Mercedes diagnostics, or using a generic ODB reader?
The car disables certain cylinders if it sees (through O2 sensors) that they are not combusting properly, however, if you're O2 sensor is faulty, it could disable cylinders whilst it shouldn't. The disablement of the cylinders end up as misfire codes on generic ODB scanners, but only show up as disabled to protect cats on Mercedes scanners.
I'd scan the car with a SDS setup and go from there.
If the car was already scanned using SDS, you might want to try and properly diagnose the O2 sensors. If those come out fine, check red sparkplug isolators, you can try the rental program at https://www.v12icpack.com/ to see if the coil pack or voltage transformer is starting to fail
The car disables certain cylinders if it sees (through O2 sensors) that they are not combusting properly, however, if you're O2 sensor is faulty, it could disable cylinders whilst it shouldn't. The disablement of the cylinders end up as misfire codes on generic ODB scanners, but only show up as disabled to protect cats on Mercedes scanners.
I'd scan the car with a SDS setup and go from there.
If the car was already scanned using SDS, you might want to try and properly diagnose the O2 sensors. If those come out fine, check red sparkplug isolators, you can try the rental program at https://www.v12icpack.com/ to see if the coil pack or voltage transformer is starting to fail
They thought it was a coil pack, and when they went to replace the pack they noticed that the pack was fine, but two spark plugs were covered in oil. He went ahead and replaced those two spark plugs and is going to take the car on a few lengthy test drives Monday and reevaluate.
He suggested that if the new plugs fix the problem, then just keep driving the car. The other option would be to do a compression test (which I'm thinking of doing just for peace of mind).
My question is, where is this oil coming from? The car does use a quart every 1000 to 1500 miles, but I have never noticed any smoke at start up / idle / or acceleration. Could the two plugs being covered in oil be the result of valve cover gaskets, or is this more likely a terminal condition like piston rings / valve guides?
Last edited by vinewanderer; Jun 7, 2025 at 11:20 AM.
Member
Joined: May 2020
Posts: 247
Likes: 58
From: Fort Worth
2005 CL55 AMG || 2005 CL65 AMG || 1989 560SEC
IIRC cylinder 6 is on the passenger side nearest the firewall.... My misfire was there as well, and those were the only two sparkplugs that were horrendously gunked up on that bank.
My car was burning a quart every 1000 miles, then bumped up to a quart every 100-200 miles recently. My pet theory is turbo seals, been meaning to look at the intercoolers and see if they're oily inside.
I thought it may be a PCV issue as well, so i replaced my oil separator (drivers side of engine, between upper metal radiator neck and valve cover)... maybe a slight change, if any, in consumption. Then, my engine puked a large a mount of oil from the filler on a hard pull through a curve, so I figured there was a pcv leak/sealing issue there. Replaced the cap just last week, and I now have to exert some force to pull the oil fill cap off with the engine running from the (newly present) vacuum.
.... That is to say, I wonder how much turbo oil seals rely on help negative crankcase pressure?
I'll let you know if I see a difference in consumption, which would probably directly translate to fouling of plugs in the cylinder that's one of the closes to the actual throttle body mounting point.
My car was burning a quart every 1000 miles, then bumped up to a quart every 100-200 miles recently. My pet theory is turbo seals, been meaning to look at the intercoolers and see if they're oily inside.
I thought it may be a PCV issue as well, so i replaced my oil separator (drivers side of engine, between upper metal radiator neck and valve cover)... maybe a slight change, if any, in consumption. Then, my engine puked a large a mount of oil from the filler on a hard pull through a curve, so I figured there was a pcv leak/sealing issue there. Replaced the cap just last week, and I now have to exert some force to pull the oil fill cap off with the engine running from the (newly present) vacuum.
.... That is to say, I wonder how much turbo oil seals rely on help negative crankcase pressure?
I'll let you know if I see a difference in consumption, which would probably directly translate to fouling of plugs in the cylinder that's one of the closes to the actual throttle body mounting point.
Last edited by JustTXn; Jun 7, 2025 at 05:04 PM.
MBWorld Fanatic!
Joined: Feb 2012
Posts: 2,667
Likes: 1,238
From: Phoenix
222 S-65
Guys RE: Oil consumption with your bent-12. Most of these cars were purchased by Octogenarians who never give it a WOT test. The rings fail to seal well when they don’t get a proper thrashing. Really. With it running well be sure to plant your right foot on the mat accelerating through as many gear ratios as there is room for. Daily. My first S-65 burned a quart every 800 miles or so when I bought it at 58,000 miles. Took until 70,000 miles of daily thrashing with regular maintenance and oil consumption dropped dramatically. Have instructed many to do the same with similar results through the years. It takes a while but it works.
OP get your charge cooling pump working/replaced and be ready for the treat that is bleeding all the air from the charge cooling circuit.
Coil packs happen in 221 cars. Clark is a good resource.
OP get your charge cooling pump working/replaced and be ready for the treat that is bleeding all the air from the charge cooling circuit.
Coil packs happen in 221 cars. Clark is a good resource.
Thread Starter
Newbie
Joined: Apr 2024
Posts: 12
Likes: 0
From: Wisconsin
2008 CL65 AMG
Thank you for your advice! Funny enough this Friday my mechanic advised me the same, to "get on it", whenever I can. Guess I was always worried I'd blow the engine doing that, but happy to hear the contrary!
Trending Topics
Member
Joined: May 2020
Posts: 247
Likes: 58
From: Fort Worth
2005 CL55 AMG || 2005 CL65 AMG || 1989 560SEC
Guys RE: Oil consumption with your bent-12. Most of these cars were purchased by Octogenarians who never give it a WOT test. The rings fail to seal well when they don’t get a proper thrashing. Really. With it running well be sure to plant your right foot on the mat accelerating through as many gear ratios as there is room for. Daily. My first S-65 burned a quart every 800 miles or so when I bought it at 58,000 miles. Took until 70,000 miles of daily thrashing with regular maintenance and oil consumption dropped dramatically. Have instructed many to do the same with similar results through the years. It takes a while but it works.
OP get your charge cooling pump working/replaced and be ready for the treat that is bleeding all the air from the charge cooling circuit.
Coil packs happen in 221 cars. Clark is a good resource.
OP get your charge cooling pump working/replaced and be ready for the treat that is bleeding all the air from the charge cooling circuit.
Coil packs happen in 221 cars. Clark is a good resource.
I did not have to bleed my coolant circuit, what I did was top it up every day or two for about 2-3 weeks, would squeeze the upper soft coolant hose to burp any bubbles accumulated there. 62-68C iAT on moderate acceleration in 96F weather, AC on. Checked for bubbles by bleeding one of the nipples at the top of the circuit after a drive to check for aerated coolant.
MB World Stories
The Best of Mercedes & AMG
New Electric Mercedes-AMG GT 4-Door Coupe Unveiled: 10 Things You Need to Know
Verdad Gallardo
6 Mercedes Models That Did NOT Age Well (But Are Somehow Still Cool)
Verdad Gallardo
Manual Mercedes? 6 Times Sindelfingen Let Drivers Have All The Fun
Verdad Gallardo
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Verdad Gallardo
8 Classic Boxy Mercedes Designs That Have Aged Like Fine Wine
Verdad Gallardo
Flawlessly Restored Mercedes 190E Evo II Heads to Auction
Verdad Gallardo
Electric Mercedes C-Class Unveiled: 11 Things You Need to Know
Verdad Gallardo
Mercedes EQS Gets A Major Update: Everything You Need to Know
Verdad Gallardo
5 Underrated Mercedes-Benz Models That Don't Get the Love They Deserve
Verdad Gallardo
SPONSOR
Joined: Apr 2021
Posts: 846
Likes: 559
From: San Jose, CA
11 E550, 16 AMG GTS, 13 S550
secondary coolant pump is going out
__________________
Alpha European Autotech
Purchase Amsoil at 25% off from me
Chris Tran, Retired Alpha European Autotech Owner
Amsoil Independent Dealer #7236674
Alpha European Autotech
Purchase Amsoil at 25% off from me
Chris Tran, Retired Alpha European Autotech Owner
Amsoil Independent Dealer #7236674
Thread Starter
Newbie
Joined: Apr 2024
Posts: 12
Likes: 0
From: Wisconsin
2008 CL65 AMG
The coolant code ended up being an erroneous stored code that fortunately hasn't come up again. My issue ended up being the two plugs for cylinder 6 being covered in oil. The mechanic replaced those plugs last Tuesday and told me I need to drive the car harder. So far I'm a week out from the fix with no issues!
