Hard start & rough idle when cold

[Bill Green]

1985 4KQ with 2.2 L starts and idles fine when warm. But when trying to
start cold it cranks longer than it should before starting and stumbles and
idles rough until it warms up. Once warm it idles and starts normally
although the tachometer says it is idling at 950-1000rpm and no matter what
I do it won't go lower. 

 

I've checked for vacuum leaks and have found none, the air filter is new. I
checked the cold start valve and physically verified it was working. The
coolant temp sender checks out fine as does thermal time switch. The O2
sensor is new and reads .5v with very little fluctuation. The duty cycle for
the ISV reads 32% + 5% -0. Using Huw's adapter harness I found that the
differential pressure regulator reads 15-16 milliamps when idling warmed up.


 

I bought a kit to test fuel pressure and using it found the system pressure,
differential pressure and bleed down pressure are all within spec. Timing is
set according to spec. Plugs, wires, dist cap and rotor all new. 

 

Often when trying to start cold it will fire for just an instant when first
turning over. I have assumed this is from the cold start valve. But then it
will just crank and crank until finally starting. 

 

Would the initial firing indicate the problem is not leaking injectors? Any
thoughts on what the problem is? 

 

Thanks in advance.