Ive been stressed to the max with rough idling problems. I am in the automotive industry in Australia and i had these rough idle problems that just came and went also for 6 months - just out of warranty. Upon asking a BMW specialist, he told me that all E46 vehicles need the coils to be changed as they are faulty - use Bosch instead of Bremi. Did that and went perfect for 4 days then back to rough idling. Then the PVC hose was changed- all great for 4 days and then same again. Frustrating......
I took it to a BMW dealership who had it for a week and all they could come up with was "you need a fuel additive". what a load of crap and waste of $180 as the problem came back after 4 days. Then they got it back and took a further week to tell me that my eccentric shaft is worn, with rockers and lifters , my oil is all sludged, and would cost about $5000 to fix!! BMW state that as i did not use long life oil that they wont provide any "goodwill assistance" as i did not use the long life oil. The stange thing i noticed was it happened when my wife did short trips. I travel 50km to work and i seldom have had the problem, yet as soon as the short trips start, the rough idle problem starts- guaranteed!
The bottom line is that they found my oil to be sludged and hence accordingly the sludge plays havoc with the valvetronics which confuses the computer into thinking that injectors are faulty. I had 2 instances of injector 1 reporting faulty, and another where injector 2 and 3 were faulty. This is of course impossible, as I have only done 37 000km.
I did not know of having to use long life oil, and ive only replaced the oil once since 2005 (after 19687km) and did so with Motul 4100 turbo light which is on the BMW approved list but ive since been told "NOT on the list for the N42 E46 engine!! ". Motul state that there oil doesn't not sludge and wanted a sample to prove so, but the dealer failed to read my email and answer me to comply with my repair conditions, so that evidence is destroyed now.
Despite all this they took all up 2 weeks to come up with this diagnosis for repair.
I started to enquire through people i knew who knew people and came across a startling discovery : a mechanic who has only just left working in a BMW dealership and was called "the whiz kid" told me the problem with my car immediately without even looking at it : He stated that the N42 engine has a breathing problem in the sense that the PVC valve can get very easily clogged and when this happens the separator cant flow properly and this sludges your oil, which in turn plays havoc on the valvetronics which cause your engine to rough idle sporadically due to all the mass sludge in your engine!! He should know as he did these warranties (if people were lucky enough to get it within the 2 year period by doing enough km to warrant a having a 2nd service at 40000- and he did TONS of them. i was unlucky (and ripped off) as i didnt do enough km to warrant a 2nd service within the warranty period. Another of my staffs friends at a dealership said that they replace the "rockers and lifters" regularly. I know its not the proper technical name for them as they are "or lifters and oar shafts".
I couldnt believe my ears. BMW stuffed me around for 2 damn weeks until they discovered this out. He even told me an instance that on a new 7 series the pvc valve actually broke down and went into the engine and completely ruined the engine!!
When i got back to work, I contacted more ex bmw techs and, also techs from with each dealership that our staff know told me EXACTLY the same prognosis - without even seeing my car as they know this problem. EVERY dealer, except the state's flagship dealer (owned and run by Head office) that repaired my car, admitted the problem and all knew it was an incredible task for ANY car to go 25000 with only 1 service. I innocently went by BMW's computer recommendation to replace the oil when it said to and that was my downfall- sticking to the BMW recommended service interval.
Of course the typical mechanic out there doesnt see these problems , as they recommend to change the oil typically every 10 000 km or 6 months, so even though they DONT use the long life oil - their customers dont get that rough idle problem. Strangely enough, many (not all) BMW customers using this long life oil, have got this same problem as me and many of you.
I was called a few days later by "the whiz kid" and he invited me to the workshop and he had a dead identical car to mine - build date 11/04 with 38 000 km BUT it was serviced the once at at BMW dealership with the long life oil. Well to my amazement, he showed me all the evidence i needed - a blocked pvc valve, sludging down the pvc hose and the manifold etc, so its obvious that in many cases - not all- that the long life oil (supposed to last 25000km) makes no difference either as the oil WILL sludge.
I' m taking my fight up to BMW as i have so much hard concrete evidence.
I hope this info help you out somewhat.
