05 CLK320 Cabriolet stumbles and hesitates - been troubleshooting for two years
Thread Starter
Junior Member
Joined: Jun 2008
Posts: 27
Likes: 0
2005 CLK320 Cabriolet
05 CLK320 Cabriolet stumbles and hesitates - been troubleshooting for two years
All,
I welcome any suggestions you may have for how to troubleshoot my 05 CLK320 cab. I swear I had her fixed three months ago but the troublesome idling problems have returned.
Here is the chronology of work done from 2021 to now (including a couple maintenence items not related to this problem). Note that the car is driven only occasionally so the mileage has only advanced by about 1,500 since 2021. All of this work has been done with the car in the 110-111.5k mile ballpark.
5/15/21 replaced valve cover gaskets and vent gasket on drivers side - had to replace one sparkplug as old one broke when removing
6/26/21 replaced EGR valve; replaced all breather hoses based on kit from rockauto; replaced MAF sensor; found oil leak from breather hose that connects below the MAF sensor, driver side that was causing a drip on the exhaust and burned oil smell, now fixed
7/31/21 replaced fuel pump and fuel filter; car still stumbles at idle after warmup
9/19/21 replaced rear brake pads and sensor (right)
11/15/21 changed oil and filter even though not driven much
10/12/22 Performed smoke test and believe there may be a leak around intake elbow below MAF sensor; replaced upper and lower gasket seals around intake elbow under MAF sensor in hopes of fixing intake air leak that is causing lean fuel trim codes. Performed extensive driving and OBD sensor data collection/analysis. CEL codes have included lean B1 and B2 codes (P0171 and P0174). Those may now be fixed revealing several cylinder misfire codes, including multiple misfires and cylinder 4 misfire. Removed plugs and they show clear need for replacement. Large gaps, I think on the thin wire Bosch platinum plugs. Also several plugs hard to unscrew. One plug (#4F) not tight in socket. Ordered new plugs.
10/17/22 replaced spark plugs with bosch OEM double platinum (7422); cleaned all plug hole threads by grinding 3 channels in one old plug's threads (like a tap and die) and running in and out of each plug socket. Worked like a charm collecting crud in the channels. All plug sockets now easily accept plugs allowing me to hand thread all the way to bottom. Ratchet only needed to tighten. OBD diagnotics indicate all systems now working correctly. Hesitation, misfiring, and poor drivability all seem to have been corrected. No incidents of any idling issues, stalling or other symptoms previously exhibited. Idle stays stedy at ~600+rpms. Engine runs very smoothly and reliably again.
10/21/22 completed mercedes driving/idling procedures to set the emissions tests. OBD scanner indicated car ready for state emissions test. 110,750 miles Passed test! Registered for two years!
10/21/22 Thorough cleaning of interior and exterior, including pulling the seats to clean carpet. New wiper blades.110,750 miles Problems appear to be all solved and she is running like new again.
7/22/23 Drivability problems have resurfaced in the past 3 months 111,500 miles, I am baffled and chagrinned to say the least. Have used the OBD scan tool to collect data. Now analyzing it.
So, attached are csv files for two trips in the car. I am analyzing them but I am having trouble developing a theory for the cause.
Some notes and observations:
Since I have failed in the parts replacement strategy I am loathe to do any more of that until I do a better diagnosis. The next parts replacement candidates would be the upstream O2 sensors, though. Everything I have read suggests they sould be replaced about now anyway. But who knows? I sure don't.
As for the smoke test I did, I found it difficult to isolate the TB so I could see whether smoke was exiting somewhere it should not. If there is another way to do it I am all ears. I stretched/secured a latex glove over the intake and injected smoke through a breather tube until the glove expanded like a balloon. I never really saw any clear problems but the immediate TB area was still flooded with smoke and made it hard to tell for sure. I also sprayed TB cleaner around the engine while it was running but never found any change in the idle that would have been associated with spray finding its way into the air intake.
Any thoughts/suggestions/theories you may have would be greatly appreciated.
I welcome any suggestions you may have for how to troubleshoot my 05 CLK320 cab. I swear I had her fixed three months ago but the troublesome idling problems have returned.
Here is the chronology of work done from 2021 to now (including a couple maintenence items not related to this problem). Note that the car is driven only occasionally so the mileage has only advanced by about 1,500 since 2021. All of this work has been done with the car in the 110-111.5k mile ballpark.
5/15/21 replaced valve cover gaskets and vent gasket on drivers side - had to replace one sparkplug as old one broke when removing
6/26/21 replaced EGR valve; replaced all breather hoses based on kit from rockauto; replaced MAF sensor; found oil leak from breather hose that connects below the MAF sensor, driver side that was causing a drip on the exhaust and burned oil smell, now fixed
7/31/21 replaced fuel pump and fuel filter; car still stumbles at idle after warmup
9/19/21 replaced rear brake pads and sensor (right)
11/15/21 changed oil and filter even though not driven much
10/12/22 Performed smoke test and believe there may be a leak around intake elbow below MAF sensor; replaced upper and lower gasket seals around intake elbow under MAF sensor in hopes of fixing intake air leak that is causing lean fuel trim codes. Performed extensive driving and OBD sensor data collection/analysis. CEL codes have included lean B1 and B2 codes (P0171 and P0174). Those may now be fixed revealing several cylinder misfire codes, including multiple misfires and cylinder 4 misfire. Removed plugs and they show clear need for replacement. Large gaps, I think on the thin wire Bosch platinum plugs. Also several plugs hard to unscrew. One plug (#4F) not tight in socket. Ordered new plugs.
10/17/22 replaced spark plugs with bosch OEM double platinum (7422); cleaned all plug hole threads by grinding 3 channels in one old plug's threads (like a tap and die) and running in and out of each plug socket. Worked like a charm collecting crud in the channels. All plug sockets now easily accept plugs allowing me to hand thread all the way to bottom. Ratchet only needed to tighten. OBD diagnotics indicate all systems now working correctly. Hesitation, misfiring, and poor drivability all seem to have been corrected. No incidents of any idling issues, stalling or other symptoms previously exhibited. Idle stays stedy at ~600+rpms. Engine runs very smoothly and reliably again.
10/21/22 completed mercedes driving/idling procedures to set the emissions tests. OBD scanner indicated car ready for state emissions test. 110,750 miles Passed test! Registered for two years!
10/21/22 Thorough cleaning of interior and exterior, including pulling the seats to clean carpet. New wiper blades.110,750 miles Problems appear to be all solved and she is running like new again.
7/22/23 Drivability problems have resurfaced in the past 3 months 111,500 miles, I am baffled and chagrinned to say the least. Have used the OBD scan tool to collect data. Now analyzing it.
So, attached are csv files for two trips in the car. I am analyzing them but I am having trouble developing a theory for the cause.
Some notes and observations:
Since I have failed in the parts replacement strategy I am loathe to do any more of that until I do a better diagnosis. The next parts replacement candidates would be the upstream O2 sensors, though. Everything I have read suggests they sould be replaced about now anyway. But who knows? I sure don't.
As for the smoke test I did, I found it difficult to isolate the TB so I could see whether smoke was exiting somewhere it should not. If there is another way to do it I am all ears. I stretched/secured a latex glove over the intake and injected smoke through a breather tube until the glove expanded like a balloon. I never really saw any clear problems but the immediate TB area was still flooded with smoke and made it hard to tell for sure. I also sprayed TB cleaner around the engine while it was running but never found any change in the idle that would have been associated with spray finding its way into the air intake.
Any thoughts/suggestions/theories you may have would be greatly appreciated.
