AzzHauler

iTrader: (3)

...when I first start the car after it's been sitting (read:engine cold), it runs so much better than when it warms up, part throttle-wise? It's in open loop until the o2 sensors heat up right, then goes to closed loop? But still reads off the maf the whole time? Runs just perfect, then the o2's start swinging around trying to get that 14.7:1 afr, and I can feel slight sputters here and there even with constant tps, and every so often a little 'buck' on shifting. Any ideas?

jimmyblue

iTrader: (11)

The mixture loop doesn't maintain a constant
0.500V O2 sensor. It lets it bounce, I think
it dithers the mixture on purpose and looks
for an -average- 0.500 (or whatever). So if
you look at the sensor voltage it's all over
the road. When it gets into the outlying
areas the road gets a little rough. My car
popped at idle since new.

At cold, I believe there is some built-in
enrichment in the open-loop settings. You
miss lean; you would have to be stankin'
rich to have a misfire stumble.

wrencher

iTrader: (2)

Cold the pcm is running the open loop program,a fixed fuel program based on load & tempurture. Hot it is in closed loop using o2 & sensors to obtain 14.7 -1.

ChrisB

It's running a bit richer until you reach a certain temp threshold - and typically you will achieve a better/more stable idle to the rich side of stoich (it just won't be as fuel efficient/good on emissions).

Chris