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&mospid=47620&btnr=11_2982&hg=
11&fg=50),
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=11225&group_ID=144
8&store=uk&dir=catalog
and
http://buy1.snapon.com/catalog/item.asp?P65=&tool=all&item_ID=11221&group_ID=144
8&store=uk&dir=catalog)
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_ID=67469&group_ID=228
&store=uk&dir=catalog).
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