A customer (in this case a friend, too, so I won't be making any money!) brings me an 87 190E 8v stick shift with an odd propensity for EXTREMELY poor running in wet weather... a real problem here near Seattle. The car seams to do OK after a day or two of dry weather, but after a day in the rain, the car will start but stumble at idle, rev but not pull load, and go out like a light when the throttle is held down, with an occasional spurt of acceleration. A prolonged warm up makes the car driveable, but the tendencies do not disappear in the rain. I've already put new cap,rotor,wires & fuel filter on the car, and checked the fuel pump relay (OK, and appears to have been recently replaced), even bypassed the relay (hot wired the pump) with no success. The OVP seems good (no other symptoms of over-voltage, but I haven't done the full diagnostic set on that), and the deceleration switch can be disconnected to no avail. The diaphragm pressure regulator, over pressure return valve, and pump (mechanical) shouldn't be sensitive to weather(?). I am going to look at (and maybe hose down) the pump tonight and see if the motor is water tight, but the day is dry so the car is running. Is one of the "brains" a likely culprit (i.e. ignition control module or injection control module)? Any notorious switches (i.e. throttle position, temperature, etc)? The weather dependency points towards electrical, but the behavior seems like cross-over. Any ideas?