Finally got round to replacing the eccentric shaft sensor on my E86. For some background, the N52 uses variable valve lift and timing to negate the need for a throttle body. It is fairly common for these sensors to go eventually, but curiously when they do they don't throw a CEL.
Symptoms for me were:
1. Poor fuel economy (down about 15-20%)
2. Poor torque/lack of urgency down low. Now that I've fixed it, it feels much lighter on its feet and eager to press on but you mightn't notice unless you had a point of reference to compare to.
3. Slightly uneven revs at idle. Not all that noticeable unless you had something to compare to
4. Eventually went into limp mode at full throttle. It only did this once, and restarting the engine removed it. Again, no CEL at any point though. This is what prompted me to plug it into the C110 and then into INPA.
The engine is still able to function, albeit using a (usually redundant) butterfly valve to adjust air/fuel mix. I had noticed some of the above, but had put it down to the plugs or coils needing replacing. It was only when I plugged it in that the DME displayed;
1. 2A37 Valvetronic, Exzenterwellensensor: Plausibility
2. 2A59 Valvetronic Exzenterwellensensor: Guide
Did some googling, and apparently the eccentric shaft sensor can get inundated with oil and fail. Sometimes you can see oil in the connector (remove engine cover, unplug, check), but mine had no residue.
Finding guides wasn't that easy as I wanted one for the plastic top N52 (produced toward end of E86 production run), and also one for the Z4 in particular (the E90/E60/E81 ones require you to remove a whole load more to get to the valve cover, whereas it is quite simple with the Z4). These two were most helpful:
1. The Pelican Parts guide (albeit for the E90) together with
2. This youtube video which was the only one I could find for getting the valve cover off on a Z4 with the N52K engine.
For parts, I used the VDO Eccentric shaft sensor (from AutoDoc), which was £168. This was significantly less than the "official BMW part" (I think closer to £300),but turned out to be the same one (the one I took out of the engine was Siemens/VDO). There are cheaper versions of this part on eBay at around £50, but given the amount of time to do this repair I only wanted to do it once (and didn't want to have a potentially inferior product).
For tools, I used:
1. Socket set (including a deep set 10mm for two of the valve cover bolts that also have the harness grounding points on them. Yup - that was a trip to halfords today).
2. Normal spanners including a 10mm (you need them for removing the eccentric shaft sensor)
3. Female Torx set including E8 and E10
4. Torque wrench. You need one that goes down to as little as 9nm for the valve cover gasket bolts. This is important, you need to get this right or the gasket could leak.
5. Torx set for removing the valvetronic motor. By the way when removing the motor, I didn't bother with using an allen key to turn the motor to it's furthest point (as has been suggested to prevent the need for calibration). I just removed it, reinstalled when valve cover back on and let it self calibrate. This is done by turning the ignition on, waiting 5 seconds, turning off and then starting the car. No warning lights, no INPA needed to calibrate etc.
I also replaced the valve cover gaskets, valve motor gasket and eccentric shaft gasket (all from AutoDoc, all Elring). Though I didn't have any oil leaks, the existing gaskets were hard as plastic and it would have only been a matter of time before they leaked.
All in all, the job took about 5 hours. This included time spent cleaning the valve cover and the mating points, and some time indoors when it started to rain (I don't have a garage). I was pleased, considering I was quoted about £300 in labour at my (very reasonable) indy.
If I were doing the job again, I would get some gasket adhesive to hold the valve cover gasket onto the valve cover at a few points (especially at corners). The N52 doesn't have the half moons like the M54, but it is tricky getting the valve cover into place and the gasket can get snagged on the top of the engine. You don't want the gasket to be incorrectly seated! For me it took time, a few attempts and a second pair of hands.
If anyone is reading this and has any questions, please feel free to get in touch.
Symptoms for me were:
1. Poor fuel economy (down about 15-20%)
2. Poor torque/lack of urgency down low. Now that I've fixed it, it feels much lighter on its feet and eager to press on but you mightn't notice unless you had a point of reference to compare to.
3. Slightly uneven revs at idle. Not all that noticeable unless you had something to compare to
4. Eventually went into limp mode at full throttle. It only did this once, and restarting the engine removed it. Again, no CEL at any point though. This is what prompted me to plug it into the C110 and then into INPA.
The engine is still able to function, albeit using a (usually redundant) butterfly valve to adjust air/fuel mix. I had noticed some of the above, but had put it down to the plugs or coils needing replacing. It was only when I plugged it in that the DME displayed;
1. 2A37 Valvetronic, Exzenterwellensensor: Plausibility
2. 2A59 Valvetronic Exzenterwellensensor: Guide
Did some googling, and apparently the eccentric shaft sensor can get inundated with oil and fail. Sometimes you can see oil in the connector (remove engine cover, unplug, check), but mine had no residue.
Finding guides wasn't that easy as I wanted one for the plastic top N52 (produced toward end of E86 production run), and also one for the Z4 in particular (the E90/E60/E81 ones require you to remove a whole load more to get to the valve cover, whereas it is quite simple with the Z4). These two were most helpful:
1. The Pelican Parts guide (albeit for the E90) together with
2. This youtube video which was the only one I could find for getting the valve cover off on a Z4 with the N52K engine.
For parts, I used the VDO Eccentric shaft sensor (from AutoDoc), which was £168. This was significantly less than the "official BMW part" (I think closer to £300),but turned out to be the same one (the one I took out of the engine was Siemens/VDO). There are cheaper versions of this part on eBay at around £50, but given the amount of time to do this repair I only wanted to do it once (and didn't want to have a potentially inferior product).
For tools, I used:
1. Socket set (including a deep set 10mm for two of the valve cover bolts that also have the harness grounding points on them. Yup - that was a trip to halfords today).
2. Normal spanners including a 10mm (you need them for removing the eccentric shaft sensor)
3. Female Torx set including E8 and E10
4. Torque wrench. You need one that goes down to as little as 9nm for the valve cover gasket bolts. This is important, you need to get this right or the gasket could leak.
5. Torx set for removing the valvetronic motor. By the way when removing the motor, I didn't bother with using an allen key to turn the motor to it's furthest point (as has been suggested to prevent the need for calibration). I just removed it, reinstalled when valve cover back on and let it self calibrate. This is done by turning the ignition on, waiting 5 seconds, turning off and then starting the car. No warning lights, no INPA needed to calibrate etc.
I also replaced the valve cover gaskets, valve motor gasket and eccentric shaft gasket (all from AutoDoc, all Elring). Though I didn't have any oil leaks, the existing gaskets were hard as plastic and it would have only been a matter of time before they leaked.
All in all, the job took about 5 hours. This included time spent cleaning the valve cover and the mating points, and some time indoors when it started to rain (I don't have a garage). I was pleased, considering I was quoted about £300 in labour at my (very reasonable) indy.
If I were doing the job again, I would get some gasket adhesive to hold the valve cover gasket onto the valve cover at a few points (especially at corners). The N52 doesn't have the half moons like the M54, but it is tricky getting the valve cover into place and the gasket can get snagged on the top of the engine. You don't want the gasket to be incorrectly seated! For me it took time, a few attempts and a second pair of hands.
If anyone is reading this and has any questions, please feel free to get in touch.
. Its worth getting the reader, as you say before going any further with buying bits 
