Oil pressure readings on gauge (again?)

[allenjdmb]

Sorry if this is too much like the post a few down, but not quite the same issue. 89 126 300SE with M103 USA. Runs great, good fuel economy, had top end done about 10 k ago. Gauge tells me, after a while of running and normal temps, that pressure is dropping to nearly zero. I know I need to confirm with a manual gauge. I'm told that on the 6 cyl cars there is a bypass valve(?), and that frequently there will be a slight buildup in the oil filler housing. Mostly it's just irritating, but I do want to make sure it's not a problem. I'm sorta thinking that the car's idle speed is a bit too low, and that may be making it seem worse than it really is. But there is no adjustment for idle on this setup, right? Any experience in improving that? If I manually hold the accelerator to 1000 RPM at idle, the pressure is fine, up over 1 bar. Thoughts? Thanks for your help.