Solution - E46 330ci sticky throttle, power surge, step change in power, unpredictable acceleration

Hi all
I am just reporting back on the solution to my "sticky throttle" / "surge" / "sluggishness at low power" / "step change in
power" problem on my E46 330ci.
Just as a recap, the car felt sluggish in first gear and sometimes, although not always, the engine would suffer a surge in power, and the car would race off. A bit disconcerting on a roundabout.
If you don't want to read my story, scroll to the bottom where you can read the solution.
Anyway, I took it to the dealer, he reloaded the software and then passed the car back to me saying they couldn't find a fault (shame on you Flagship BMW Dealer who will remain nameless but is not too difficult to guess). I took it to an independent (www.claytoncars.co.uk), they couldn't find a fault code either, but offered to keep it for a few days to try and identify the problem. In the meantime, surprised that there was not a solution to the problem on the BMW Central Knowledgebase (if one so existed), I trawled the internet. I found about half a dozen other people who had suffered the same problem, one of whom found a solution (we will come onto that in a sec) and others who just lived with it between dealer visits. I also found a few other leads, such as clogged injectors (http://www.injectorcleaning.co.uk/spray.htm ), dirty MAF (http://www.fordscorpio.co.uk/cleanmaf.htm ) - The car has done over 100k miles.
I bought some fuel system cleaner (http://www.holtsauto.com/products/146.htm ) and put a HUGE dose in with the fuel hoping to clean the injectors etc. (was thinking of ultrasonically cleaning the injectors too), this didn't appear to do much, and I am currently waiting for some carb cleaner to clean the MAF (don't need it now!).
On the forum side, I had lots of responses, some just lived with it, others had had software updated, pedal positioning sensors replaced etc., but one guy (on this forum - thanks Paul!) found a solution when the Check Engine Light came on, fault codes pointing to a cam shaft sensor fault. Dinan replaced this and the O2 sensors at the same time.
My car had no faults stored...
I logged some data driving around town using my TekMate (http://www.tekmatetools.com /) and although the scanning rate is low, you could see the operation of the O2 sensors regulating Lambda probes - http://www.realoem.com/bmw/showparts.do?model=BN52&mospidG620&btnr _2982&hg&fgP), for normal operation (not foot to the floor) they should bounce between 0.9 and 0.1 in a sinusoidal fashion (some websites say they should go between 0.9 and 0.3), however, one of mine seemed to be sitting at 0.9 for extended periods of time, then down at 0.1 for extended periods of time. I was unsure whether this was the cause or the effect of the problem and indeed if my TekMate was quick enough to monitor these changes, was it missing some of the points on the sinewave?
I took the car for a second opinion, but not to the "no fault codes no problem" dealer, but to a Bosch injection specialist (http://www.lodwayservicestation.co.uk /). He put it on his machine, which in reality was no better then my TekMate, and we saw the same effect. He wasn't sure if it was the cause or effect but told me he had seen similar things on other cars and changing the lambda sensor had cured the problem.
I booked the car in to have the sensors changed, he offered me NTK sensors at 60GBP each (dealer price for genuine BMW ones - 160GBP each), however, when the time came, after leaving the car with him all day, he admitted defeat when he told me he didn't have the right tools for the job, even though he had spoken to the Snap On man etc. I was told that I had to take the car to a dealer as bespoke BMW tools were required.
Anyway, I wasn't going to be defeated, so I called my independent again to talk to them about changing the sensors. They told me the sensors did not normally fail and if there was no fault code they would not consider it worth changing them. I still wasn't going to be defeated, so I got the Bosch catalogue and looked up my vehicle, identified the sensors and ordered them from my local Bosch agent (http://www.bae-bristol.co.uk /) at a cost of 70GBP each.
I also needed some tools, I looked to my TIS (ETK dealer CDs that I got off EBay) and in the Bentley manual and checked the special tools needed. They didn't look so special, and I thought they looked a bit like some Snap On tools (http://buy1.snapon.com/catalog/item.asp?P65=&tool=all&item_ID 225&group_ID48&store=uk&dirĘtalog and http://buy1.snapon.com/catalog/item.asp?P65=&tool=all&item_ID 221&group_ID48&store=uk&dirĘtalog) so I attempted to locate my nearest Snap On van. The man with the van who supplied Bristol was not interested in returning my calls despite half a dozen messages (shame on you too - I wanted to spend money with you!!!!), but the man with the van near my parents (50 miles away) did return my call, he didn't have the tools I wanted, instead he had a Snap On Blue Point 7 piece Lambda Sensor tool set, LTS3768, which contained versions of the above, but black, of which I ended up only needing the 22mm (7/8 actually) slotted socket, used in conjunction with my flexi-head ratchet (http://buy1.snapon.com/catalog/item.asp?P65=&tool=all&item_IDg469&group_ID "8&store=uk&dirĘtalog). Sure, it was not plain sailing, it was fiddly, and it took about 1.5 hours to change the pair, but that included explaining to my neighbours, what I was doing, why I was doing it and how a lambda sensor worked! The worst bit was rerouting the wires, but a little bit of perseverance sorted that out!
Lo and behold, when I removed the lambda sensors, which were white like toothpaste, they had the same Bosch part numbers as the ones I was fitting (0258 005 259 and 0258 005 177).
I bought the car with 85k miles, and it misbehaved from then, but being new to the car I didn't know if it was me or it... Why did it (or they) fail so early? I don't know, there are those that say change them every 60k miles, or every 100k miles, my car uses 1 litre (or 1 quart) of oil every 1000 miles (which BMW say is normal) and this can't be helping.
Whatever the case, I fixed it, it has transformed my car and I am happy!
Summary ======= Sticky throttle / surges in power low down / step changes in power? Change your two pre-cat O2 sensors (in the manifolds)....
Thanks to all who corresponded with me and ultimately helped me find the problem.
Nick
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"Pashlipops" wrote

Wow! My hats off to you for being so persistent and dedicated to getting to the bottom of this. As far as early failing lambda sensors, the one on my A4 1.8T (a Bosch part as well, AFAIK) started throwing error codes as early as at 40K miles. However, it did not cause any surging or anything. Also, my g/f has an '01 Jetta with a 2.0 engine, and it also just threw an error code related to the O2 sensor... at 36K miles.
Cheers,
Pete
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It is interesting to note that this (or these) lambda sensors were not detected as failed. Gone (nearly) are the days when a good mechanic could identify the fault by ear/experience/understanding of the vehicle operation, instead we are left with reliance on fault codes only.
I had an email from a chap telling me that this was not the problem with his car as his exhibited the problem since new (along with many other people) and the dealers were at a loss as to what the problem was. There is no reason why the lambda sensor could have been defective from new, a bad batch perhaps, and since the DME couldnt throw up a trouble code, the dealer could not identify the problem. I bought my car secondhand, and it could have had this problem since new.
Next job is to solve my P1619, which looks like I need a new thermostat, and believe me, I wasnt sure if the lambda sensor was the whole cure, but reading the Bosch Automotive Handbook I understood that the lambda sensor is the kingpin of primary closed loop control.
Nick
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Mainly because dealers don't seem to have good mechanics anymore, but rely on fitters of new parts. Despite their sky high labour rates.
--
*I wished the buck stopped here, as I could use a few*

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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