Why does a bigger cam cause a rich cold idle? When the outside temp is lower than 50* my 350 idles rich and rough. Warm it idles fine. My cam is small, 206 intake duration, 212 exahust, 110 lobe separation. Just curious, if the computer is in open loop why it runs rich & rough, the amount of fuel shouldn't change until the O2 sensor is looked at in closed loop, right?

 

Yeah but if your idle MAP voltage is too high (too low of a manifold vacuum), the ECM will dump more fuel into the engine UNLESS you have custom burned an EPROM to compensate. Seems to me that 110 lsa is too low...

 

I thought that 110 lsa was too tight as well. But thats what compcams gave me as the best for my combination. 12-249-4. Low vaccum at idle would cause a rich mixture, but shouldn't idle vaccum be the same cold or warm? I will get some readings tomorrow. Is the map sensor looked at in open loop?

 

If idle vacuum is higher when warm, that sort of indicates a vacuum leak but can also relate to rings and stuff like that.
EVERYTHING except the O2 (lambda) sensor is looked at in open-loop. Closed-loop simply adds the O2 sensor to the equation.
In fact, the car will barely run without the MAP and coolant temp sensor.