89 Formula 350. What are some possibilities as to why my car is not going into open loop operation? (just noticed this)
Also stumbles off idle when started after allowed to cool...but not only when cold, if idling until up to operating temp. then when throttle applied will still stumble until it revs out of it.(this has been going on for some time).

 

Probably mean closed loop operation? This is where the fueling is controlled via feedback from the O2 sensor. How can you tell it isn't going into closed loop?

As for the stumbling, I would start with the basics: plugs, cap, rotor, plug wires, clean the throttlebody, check timing, check fuel pressure.

On a MAF car it is important to not have any airleaks after the MAF. Check the MAF bellows between MAF & TB. Connections must be tight, no leaks, check for cracks or splits in the bellows.

The MAF itself may be bad, tap on it (gently) while engine is running, any stumble means either bad MAF or bad connection(s) to MAF. Disconnect MAF and see if the car runs better. If so, MAF may be bad.

Other possibilities are leaking injectors or a bad TPS sensor.

RBob.

 

thanks for the reply... I noticed with an ezlink scanner, while at full throttle it showed it was in closed loop... should be open. I didn't really look into it or check it upon cold start to see what it indicated(open or closed).

 

Closed loop during WOT is normal. Learn is turned off, BLM locked at 128 if was less then 128, locked at whatever it was if > 128.

RBob.