o2 sensor not cycling at idle

[ramsack]

i have been reading and searching all day about this. all my measurements are with a multimeter connected to c-56 (oxygen sensor check connector) in the passenger side kick panel.

my old o2 sensor cycled when in cruise or light throttle. with the old o2 sensor the car would start idling really bad sometimes say in a drivethrough like the car has cams, and the exhaust smelled like a carbureted car (not really rich, just that muscle car exhaust smell.) basically not idle, but every other point in closed loop. so i got another one because i have been having high idle while coasting issues.

so the new one makes my creeping idle disappear about 95% of the time now. i have tested for boost/vac leaks, ignition system is fine, coolant temp sensor is on the money, tps voltage is 0.46v, closed throttle switch is functional. tested at the o2 connector for 12v, got that on the red wire, both grounds have good grounds, and i can assume because it's logical that the signal wire has good connection because i am reading it inside the car. tried messing with fuel pressure, it was a little low, about 33-34 psi, so i raised it to about 37, no difference. sitting at idle the o2 sensor will sit around 40-50 mV, and cycle upwards once every like 3 seconds, and sometimes will do a repeat soon once, but it's never ever steady.

i really don't know what else to do here. it seems like it is stuck in open loop? i may have a small pre-O2 exhaust leak, i really have no idea how to test for this. i haven't had the car rough idle and stall with the new o2 yet, but just once right after i put a new positive battery terminal on today, so i think that was just due to the ecu being reset because it cleared right up. also with the old o2 when it would idle like crap and stall, it would carry on for maybe 2 or 3 more start-ups and then clear up. the only thing i can even think at this point is maybe ecu. the caps did leak, and i did replace them, and the board traces got all bubbly a bit, but the ecu works and the car drives fine and is perfect in every aspect except the o2 not cycling at idle.

anyone have any thoughts? thanks.

 

[toofast82]

Yes, in closed loop, it should cycle as you are aware for correct operation.

Do you have a custom chip in the ecu, where closed loop was turned off possibly? If you send me the .bin file, i can confirm this

Is the wiring to the coolant sensor in good shape? 1gs have a tendency where it splits from the connector

I would look into the ecu board damage. Send it to steve or jeffo and have them check it out. When i had my ecu socketed, my ecu had a ton of trace damage but still ran.

 

[ramsack]

i had socketed the ecu myself, as i am good at that, and i was missing the stock eeprom because the previous owner threw it out, so steve here on the boards burned me a stock e931 chip. if i give it even a little gas and idle it to maybe 1000 instead of 750 it will cycle. i guess the wiring from the coolant temp sensor to the ecu would be good to check. the car usually runs like total ass when it is cold. about the board, if i get this o2 stuff figured out without having to send it out then i won't have it fixed because i plan to just get an aem standalone.

EDIT:

just tested the resistance between pins 20 and 24 on the ecu plug (being unplugged from the ecu) and it was 600 ohms, which is about right for the temperature at which the car was currently.

 

[ramsack]

got a reading of the o2 when the idle goes crazy. it just stays at 8 mV. still no idea what else to even consider besides the ecu, in which case i have nothing to compare it to.