95 Concord 3.5 Cold Start Problem

When the temp is 35 or colder it wont start, it tries. When the temp is
warmer fires right up and runs great. I got fault code for lean 02 sensor
and replaced them both. I get no fault codes(12) but nothing for the EMC.
Are there any other ways of checking out the computer? I have the shop
manual but not the electronics addendum. Thanx.

 

I had a bad idle when cold problem on an '89 Shadow 2.5 L. It showed no
codes. Someone told me to re-torque the throttle body to the manifold, and
that straightened it right out. I don't know if it will help you, but it
won't cost you anything, and it may work. What was happening in my
cicumstance is that when it was cold it idled terribly, (there was a slight
air leak between the throttle body and the manifold and it ran too lean).
Once it warmed up the parts expanded and it ran great. Re-torquing the
throttle body fixed it right up.

 

Further probing of the computer requires a scan-tool.

That said, there are a few possiblilites that spring to mind. If you
make the assumption that, "Hmm, maybe those O2 sensors weren't really
bad, but were actually SEEING a lean mixture..." there are a few things
that can cause that while leaving drivability pretty much normal. Check
the fuel pressure and see if its in spec. The computer doesn't actually
measure the volume of fuel it injects, it makes an assumption about what
the fuel pressure is and then gates the injectors long enough to put in
the right amount of fuel. If the fuel pressure is low, the mixture will
be lean. IF the fuel pressure bleeds off overnight, that can further
aggravate cold starting first thing in the AM. If the fuel pressure is
in spec, you might have a vacuum leak somewhere that could lean it out
enough to make starting difficult. Also, the charge air temperature
sensor or the computer's coolant temperature sensor could be faking the
computer into always thinking the engine or intake air is hotter than it
really is, and the computer would lean out to compensate (or more
specifically, fail to enrich enough to start when its cold.)