Bmw 2.8 z3 surging idle

[tvralfagtv6]

For any one who has a problem with a surging idle i.e idles ok and then
suddenly starts to go from say 600 - 2000- rpm every couple of seconds. before
you go spending on o2 sensors , air flow meters etc. give a little thought for your little water temp sensor. I paid around 120£ for Bmw diagnostics test to tell me this. Hopefully this post saves someone some money one day. The sensor is around 11£ and interstingly has a considerable effect on the fueling cycle.

[pdavison]

Have an idling problem, but in my case just as the temp guage moves out of the blue sector ( as the thermostat opens) the engine stops. BMW have already replaced the thermostat twice anfd it worked for a while.

[rlk500]

I had something similar with my 2.8. Only used to do it in the cold. My independant suggested that there is a known issue with the camshaft sensor that can cause this. However, they ran the diags and said that the sensor was working fine. They then said that there were a number of Engine Management updates available, these were applied and the problem is gone.

[tvralfagtv6]

To be honest I am not overly impressed with the bmw management system it works great
when everything is new but is very sensitive to vacum leak this valve or that valve not opening correctly etc. Cars when they are older need a little bit more freedom
for error than the bmw system gives it.
My one used to do the idle surge just out of the blue zone before it warmed up fully. The temp sensor has 4 pins two out puts one i guess goes to the guage the other to the ECU. Although the guage on the dash was fine the input to the ecu was reading 140degrees c the ecu then leans off the engine goes to die the management catches it etc etc. one surging idle. I have bought a second hand airflow meter as a back up for the future

[rlk500]

Totally agree, my 1978 RS2000 idles better with a race cam and twin 48's..........the only reason it stops, either it runs out of petrol or I forget to turn the fuel pump on........