Hello All! Its been years since I've been here but now I have some information to share, and need some advice too.

I had what can be described as a surging idle. Sometimes car is fine, but with increasing regularity until it occurred on every journey and then immediately after turning on. At speed there was no noticeable problem. The when idling, the revs would drop till the tacho hits zero, then rev to correct itself causing a surge in power. If in gear this forces the car to lurch which is embarrassing.

LHM came on onece or twice. Sometimes started in low power assuming 6 cylinders. Sometimes the red check engine light came on.

I took the car to a garage on dec 12th, and got it back two weeks ago no better, with a bill for 1x new MAF and 3 hours labour. Joke. This is the test procedures I have taken.

1/ Pull individual fuel pumps fuses
RESULT: pulling the fuse for pump 1 makes no difference, pulling pump 2 fuse stops the car within 3 seconds (on the next idle sag before the high rev)

Because the garages misinformation (telling me DK motors are at fault) I went through the following

2/ Rebuilt and cleaned DK motors. No change. Open and close cleanly.
3/ Swapped Coils over. No change.
4/ Swapped MAFS over. No change.
5/ Garage had seen the CPS sensors were sending a signal, though one went off - presumed it was the aftermarket chips, removed these and then the CPS were both reporting RPM.
6/ Spraying easystart to check for vacum leaks
7/ New fuel filters
8/ Battery check - they are fine I get about 50 starts from a charge without running (during my testing).

Car is in good condition with having the folling parts replaced under my tenure
Rotors & Caps
Sparkplugs & complete spark lead set inc sensors
Intake manifold gaskets
Was chipped, but now BMW standard chips back in
Fuel lines
Injectors professionally cleaned and flow matched
Vacum return hoses + valve (crank ventilation?) Other vac lines to DK motors as well
Banjo bolts
Lambda / O2 Sensors

Ok at this point I'm fairly sure its not the sparking or the fuel flow lines. Something to do with the fuel pumps because it runs fine with one fuse out - when put back and pulling the other one it dies straight away. Runs fine at speed.

Assuming no CPS problems, I cracked on - this is the procedure to test your fuel pump system

1/ Check fuses 23/24 - Replace - try shorting with copper cable in case
2/ Relay checks (blue in EML box) - tested resistances and heard the clicking. Swap over & see if problem swaps sides (mine did not). Run on approx 1.5V in closing the 12v power to pump.
3/ Short relay 30&83 sections (see diagram on side of relay) this provides power to the pumps for sure. Listen individually. Note that one relay also activates the DME cooling fan (scared me).
4/ Check that you get 12v at the fuses from the relays.
(NOTE: Relays only active when running or cranking, sometimes for 1 second on making position 2, but not always)
5/ Remove rear right hand (UK driver side) seat and access plate. Remove and re-insert round 3 pin cable. As you look at it top pin ground (grounded by DME) Left hand pin pump1, right hand pump2.
6/ Check continuity from fuses and relays to these pins.
7/ Put small wire into each pin of the connector and re-attach. Tricky. Use these to check you are getting 12v as expected from the front (in case a wire from front to back is bad).
8/ I have checked resistances across these pins. Ground to either pin is ~1.5 +/-0.5 Ohms, pump1 to pump2 is (suprisingly) about 1 Ohm.

At this point I still had no joy. Everything is as expected. Continue!

9/ Remove pumps
10/ Check the bolts to the pumps
11/ Jury rig fuel pump to a 12v battery. Beware sparks + Fuel!
12/ Compare pump operations - few seconds so they dont burn out. Beware about 200ml of fuel will eject!

At this point I find an anomoly - Both pumps gush from the top mounted ejection port, at visually the same rate. Pressure unk at this point. However! Pump 1 (the one that was detected bad by pulling the fuses) also leaks fuel at the top of the pump, near the electrical contacts. Seems to be coming from the white bearing at the centre of the pump.

I'm assuming this is the problem, but before I order the £400 assy (both pumps, housing and level meter) from bmw (they only have the full thing) - I'd like to ask if anyone has experience of this kind of fault with a pump.

If no one knows I will swap the pumps over, re-install the pumps and then see if the fuse that upon movnig causes the car to die swaps as well. For my own refernce its currently fuse 24 that I remove to cause this death.

Best regards to all. I'll try to add a picture of the top of the pump in a moment.

Nathan