Stumbles at Idle

[JMI]

The Car: 1989 535i Auto 125,000 miles

The symptoms: Happens only at idle (about 700 rpm). The engine will start to stall, rpm dropping off, and then will surge momentarily to about 1100 rpm and then settle back to 700 rpm. Sometimes it will completely stall. I can usually prevent this surge/stall by slightly stepping on the accelerator.
There appears to be no regular pattern when this happens except maybe when slowing quickly.
Stomp test gives 1444 - no code.
Can't find any vacuum leaks, but have not ruled that out altogether.
Have cleaned ICV throughly. It buzzes when engine runs. Resistance is in range -approximately 40/20/20.
Throttle Position Switch checks out OK.
Tempted to change out ICV but don't want to spend $145 bucks for nothing.
Been wondering if it could be a fuel delivery problem but wouldn't that show up at any speed?
Any ideas what to try next?

TIA

Jim

[632 Regal]

fuel pressure or vacum leak is my guess. Did you reboot the computer yet?

[JMI]

fuel pressure or vacum leak is my guess. Did you reboot the computer yet?

Did the shogun reset if that's what you mean.
Wouldn't a vacuum leak be more steady instead of this intermittent deal?

Thanks

Jim

[califblue]

if you would have used the Search feature ...you would have found this...
http://www.bimmer.info/forum/showthread.php?t=21305

[JMI]

if you would have used the Search feature ...you would have found this...
http://www.bimmer.info/forum/showthread.php?t=21305

Going to check the crank position sensor and the oxygen sensor now.

Thanks

[JMI]

Going to check the crank position sensor and the oxygen sensor now.

Checked the crank position sensor (pulse generator) and the resistance between pins 1 and 2 is 540 ohms on the dot. So that's good.

The oxygen sensor is going to be a little harder to test... have got to find it first

Jim

[BillionPa]

if you have never replaced it, it would be good to do so, since it affects fuel econ as well.


.... check your distributer and ignition coil.

[JMI]

if you have never replaced it, it would be good to do so, since it affects fuel econ as well.


.... check your distributer and ignition coil.

The oxygen sensor was replaced by PO about 20,000 miles ago. Replaced distributor and rotor as well as spark plugs and ICV, that still hurts. Still no go

About the ignition coil, as per Bentleys:
Primary Coil, terminals #1 and #15 should = 500 ohms + or - 10% / reading below 200 ohms.
Secondary Coil, terminals #1 and #4 should = 6000 ohms + or - 10% / reading 9700 ohms.

Would tend to indicate it was bad but I'm wary of throwing more expensive parts at the problem. I have a hard time understanding how if the coil is bad that it only shows itself at idle.
Could someone explain that?

Thanks

Jim

[BillionPa]

have you replaced your DME relay?

[JMI]

have you replaced your DME relay?

Replaced DME & Fuel Pump relay a while back - 5000 miles ago.

Jim