4.3 s10 runs rich. -20 STFT begin while engine still cold

1997 4.3 s10 had irresponsive O2 sensors and lean condition. The new sensors i got seem to work normal looking at the graph but i got the wrong part number.

i dont know if they are the cause of my rich condition because also my MAF sensor is reading 7 or 8 g/s at idle and even putting a rag to restrict some flow of air i still get a high reading. i can only get a low g/s reading if i create a vacuum leak.

now i have the correct part number for my O2 sensor but is it going to fix my rich condition or should i try something else first?


the correct part is 25312200 and by mistake installed the delphi 25612200

Typically you should see 4-4.7 g/s at idle on this engine. 7-8 will cause a rich condition.

What is the idling RPM? Is it elevated?

What is the CALD LD at idle? Anything higher than ~30ish indicates the MAF is reporting on the high side.

Regardless of what O2 sensor you installed the MAF at idle is way to high.

Did you try cleaning the MAF hotwire?

rpm at idle is around 650 but it acts weird on cold startup it rises to 1500 and drops quickly to 650

im sorry what does CALD LD mean?

i did clean it and made no change. then i also tested a new maf sensor and the reading was still the same

BrunoPecego wrote:

what does CALD LD mean?

I think he refers to calculated load...

Load stays around 3 to 5% at idle.

Does the pcm opens the IAC valve if it cant cut off any more fuel? my trims are maxed out and i get a 8g per second MAf reading