A good, tough problem- 300e occassional stall after warm-up

[r_p_ryan]

I have a 92 300e that occasionally stalls at idle after about a 10-minute warm-up. It will refuse to restart for approximately 20 minutes. Then it will restart fine but hesitates off idle and runs fine when RPMs get above idle speed. No dash lights are illuminated when the car is stumbling off idle and there are no trouble codes. After about another 15 minutes of driving it runs perfectly with no hesitation. So it runs fine when cold and runs fine after fully warmed up. Seems to happen if the car has been sitting for a couple of days. Last week it on a freeway off-ramp and had to get a push to the side to wait 20 minutes. I can definetly do without that experience again.

I've removed and resoldered the OVP, no difference. It is Hungarian and the larger internal coil heats up. That seems abnormal to me. I also checked on my 300te (which runs fine) and the OVP seems warm also.

What does the idle switch do? I connected a multimeter to the idle air valve (read 8v when cold, went down as the car warmed up) and watched as I activated the idle switch. I also removed the plug to the switch and directly bridged it. Nothing seemed to happen at the idle air valve, in other words the voltage didn't deviate. Is that right?

What's the best way to measure fuel pressure (I have two 300e's, so I'm fine with purchasing tools that are reasonably priced)?

Thanks,
Robert