I am having a regular saga trying to diagnose my idle/ECU/fuel issues. With the J3 chip in, engine cuts out for a second or so, several times, just before reaching operating temp; but not with J3 removed. I have left the chip out to try to diagnose the underlying issues.

Symptoms (with J3 chip removed):
- rough, jerky idle
- hunts 700-900 rpm, especially after giving it a burst at WOT
- poor fuel consumption
- cloud of grey smoke on hard acceleration

Testing done:
- TPS is new, shows 4.08v at idle, .61v at WOT
- O2 sensor shows constant .8v at idle, varies between .7 and -.1 (reverse polarity!?) at anything above idle with no load. Snapping open the throttle gives instant -.1v (negative), then comes back to .7 or so. Sensor shows 9 ohms resistance.
- coolant temp sensor works fine (.8v at operating temp)
- have swapped ISC valve, no difference
- have swapped ECU, no difference (still cuts out with J3 chip in)
- plugs look fine: white to light brown insulators, no fouling
- only diagnostic code is cam angle sensor, but can cam sensor cause this?

Anyone have any ideas? O2 sensor out of range? Vacuum leak? Fuel pressure regulator? Thanks all.

Done a bit of research. The O2 sensor is supposed to read between .1v and .9v, and the ECU will try to keep it around .45v, equivalent to 14.7 AFR. If the sensor is contaminated (by silicon, damaged insulator, etc), it will show a lower voltage, and the range will shift downwards.

If mine is reading -.1v to .7v, that would suggest a downward shift of .2v. So, if the ECU is trying to achieve .45v, it is actually over-fueling, as the true voltage is .65v. Is that rich enough to show the effects I am seeing? Also, the fact that it doesn't move from .8v (full rich) at idle must indicate a problem.

Hey Dude,

Had all those symptoms on my BA V8, turned out to be the MAP Sensor. Your's might have a MAF sensor instead of a MAP Sensor, or it might have both. Check all your vacuum lines too.

Good Luck,