Been having this ongoing problem with the 1989 535i stalling at idle. Have checked all the sensors/switches, ECT, CPS, TPS, and AFM. Replaced the ICV, distributor and rotor, and plugs.
Today I checked the O2 sensor which has less then 20,000 miles, it was OK.
I also finally got a fault code I could read (the CEL stays light now) it is #1222 which in my car means too rich/lean an idle.
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So as for the fuel pressure test I did today. With the car idling, the pressure was 35.5 psi. Seems low as per Bentleys (43.5 psi, +/- .9 psi). Pulling the vacuum hose off the Fuel Pressure Regulator caused the pressure to rise (as it should per Bentleys) to about 45 psi. With engine running and slowly clamping down on the return from the FPR the pressure rise rapidly till it was off the gauge (0-60 psi gauge).
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This appears to suggest a bad FPR? If it was the fuel pump the pressure shouldn’t jump as the return is clamped, right?

That does sound a like a bad FPR. Replace it a see what the idle pressure winds up at.

old school bump. I have this problem right now and the indy shop cant figure it out. Any help???PLEASE!

What was your residual pressure? Key off engine off and wait two minutes after running.

I just completed installing a FP and FPR. My problems were intermittent and I could not isolate the problem.

If you slightly clamp off the return line, with a properly operating pump, the pressure SHOULD rise (Jump) as the pump is trying to push the fuel and it can't get it anywhere. Be careful the pump can put out a fair amount of pressure and you can blow something else.

As suggested by bmdubside, check pressures once shutdown and if it drops, isolate it to the supply side or return side.

You can also perform a volume test - it is in Bentley's.


Don