This is not a question I'm just putting this out there for people to help with lean running issues this is my case. So decided I had 5 days off work nice mini vacation/public holiday spree so was going to replace some things on my 2006 C180 Kompressor with the sport package. M271 engine so I was taking the time to replace the PCV valve and hoses as well as 2 pulleys and the serpentine belt while I am at it. Had no problems but I wanted to do it as preventative. Got in nice and removed Airbox with that horrible to reach spring clamp if you don't have the right tool, removed intake manifold, fuel rail, injectors and throttle body. Decided to replace all the injector o-rings and intake manifold gaskets all 5. Removed the eaton supercharger and started cleaning it all and man was it dirty, had the car about a year now and serviced it myself once when I got it replacing all brake discs and pads, oil, oil filter, fuel filter, air filter and cabin filter. Bought spark plugs then but decided for cheaper NGK copper v power plugs as my budget was tight after it all. When removed the old bosch platinum plugs I saw they were still good so put them right back after a cleaning with a brass brush. Now back to the cleaning and replacing of hoses and valves etc. did all the work was very meticulous when installing new hoses, seals and gaskets. Previous people that worked on car torqued the intake manifold and fuel rail bolts so tight it bent the fuel rail brackets so had to straighten them back up. After almost dying with a jack deciding to buckle while I was busy inserting the 6ton stand for the car got out fast enough when I heard a creak but damn side sill got damaged, will search for one at a scrapyard. Anyway all said and done everything back together and decided to put the new cheaper copper plugs in. start the car and after 5 minutes of idle get P0171 lean on bank1 code and CEL. First impulse was vacuum leak so checked for vacuum leak with MAF spray at all points that could be leaking where I worked, nothing.. Okay take car for spin after clearing code and checking short term fuel trim, idle 25% damn thats high but driving the car and stepping on gas it hovers between -5% and 7%. Still not right, thought I hurt MAF sensor when cleaning? check MAF readings all good... Okay what the heck, check MAF with multimeter, tests all good. Check O2 sensors even though I did nothing with them, all reading good.. Injectors maybe? Nope all good, I cleaned the throttle body really good it was pretty dirty but but not so bad, check throttle absolute position and all seems okay according to ECU. What can it be??? Car runs fine but idle is not good when coming to stop but mostly its fine, no CEL. Checking STFT but still high 25% at idle. Speak to mechanic buddy of mine and he mentions before looking at vacuum leak what spark plugs do I have in? Tell him the NGK LFR6A-11, he says "Wait you don't have OEM spec platinum or Iridiums in? Change them back and test again!" Get home and swap them, bam problem all gone STFT 0.00% idle and all good again. Buddy tells me he had a similar problem with a chev lumina V8 once with cheaper spec plugs.

So learned something new, never cheap out on plugs even though it says its an alternative for your car. Spark plugs can make your car run lean so check there first if you did a change and getting lean errors. Stick to the good stuff! Apparently he says the resistance are different in the plugs and the coils are specd for the OEM plugs with their specific resistances

 

hello I have the same problem as you write about. but what spark plugs did you put to fix the problem?