e28 warm weather woes

[Monty Hogan <hoganm@xxxxxxxxxxxxx>]

My wife's '86 535i is misbehaving--again.
It starts fine when cold, but when the engine is up to temperature (less
than a minute on really warm days) it starts to bog down/hesitate and
becomes difficult to keep running. Once the engine has been run/warmed and
you turn it off, it's very unlikely for it to start again and keep running.
You have to wait a couple hours for the engine to cool again before starting
once again. With temperature being the big factor to this behavior, I tested
the Coolant Temp. Switch. Seems to be fine. I've replaced some suspect
vacuum hoses, checked the intake bellows, the air-flow sensor/flap, replaced
the air filter, checked the oil filler cap seal and dip-stick seals, tried
disconnecting the Oxygen sensor to see a change in the condition (no
different), and disconnected the thermo-temperature switch to keep the
cold-start valve from getting the signal to avoid sending extra fuel into an
already warm engine, if the switch was malfunctioning. With no luch as of
yet, I'm getting the feeling it's either leaking fuel injectors, or a
leaking cold-start valve that's allowing too much fuel into the mixture when
the car has warmed. Also suspect is the fuel pressure regulator (vapor
lock). My questions are these: 1) can the cold-start valve, if faulty/eroded
still leak fuel even when it's shut off from any electrical signal (I'm
assuming yes) and 2) what's the first steps I should take to diagnose the
problem (and am I even on the right track?)?  Any insight is appreciated!

MMH
87 325is
83 R80RT
Wife - 86 535i 

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End of bmw-digest V9 #1841
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