Mazinger4: I don't have a separate fuel pump relay, in my car it is embedded in the MAS. I need to figure out how to run direct power to the pump to see if that's a problem. I think the fuel pumps/pressure are suspect. Thanks for the tip!

Neil: We have the exact same symptoms. I have a fuel pressure guage on order and am going out of town this weekend. The car will sit for a few days. Then I am going to connect the fuel pressure guage with a "T" and test it. I am sure it will stall, I just want to see what the fuel pressure is like when it stalls vs when it is fully warmed up. Last weekend it sat, and I loaded up the tools and let it stall. I sprayed varying amounts of ether (quick-start) into the throttle body and nothing happened. That somewhat tells me that the ignition system could be the culprit.

I also purchased a DMM with duty cycles. At idle, when the car is acting up and when it is running perfectly, the duty cycles are all over the place. Over 2500 RPM they stabilize at around 35%. This tells me that I might have a vacuum leak. I started another thread on hunting down vacuum leaks, and people have contributed some excellent advice there. I pulled up the carpet on the passenger side and checked the volts coming from the O2 sensor. They ranged from .01 to .9 volts. So that seems to be okay.

I checked the ignition with a strobe light and got unusual results. This also tells me that perhaps the EZL is the culprit. The wires, cap, and rotor are all pretty old, but I dislike the idea of throwing a couple hundred dollars on a guess. My car should be somewhat easier to trouble shoot because sometimes the rough idle progresses to a complete "refuse to start" syndrome. When this next happens I am going to connect the six spark leads to a set of six spark plugs that are arranged in firing sequence in a strip of aluminum bar stock that is grounded to the chassis. This way when I am cranking the car over I can verify that the plugs are firing consistently, brightly, and in the correct sequence. I'll post some pics of the rig when I'm done assembling it.

Regarding the switchover valve - thanks for checking that system. We now know that's probably not involved and you've saved me time there!

Regarding the fuel pump safety switches - I remember seeing somewhere that there's a way to interrogate the MAS, I think it is on pin 14 of the X11/4 plug but I'll need to go back to the CD there. I would have thought that this would cause a complete shutdown instead of rough idle/occasional stall, although I have heard of these symptoms caused by bad relays and pumps. I think this, possible vacuum leaks, and the EZL are where I'm going to focus. The fuel pressure guages should tell the story on the complete fuel supply system. I'll know alot more when I get back on Sunday afternoon and do another phase of testing.

Good luck and thanks for the tips! I'll keep things posted.

-Robert

__________________
89 300te 222,222
92 300e 190,000