Troubleshooting rough running - got a ScanXL graph!

[jimstolz76]

Yeah, the car is in park while it's warming up. You can drive the car while it's doing this and it will still click over and suddenly run fine just the same as if you left it sitting in Park.

The spike after the white line was me hitting the gas. I should record again with the throttle position on the graph.

Cool program! Probably total overkill for what I'm doing, but that's half the fun.

[thehunterooo]

looks like a good program, im sure it has many more applications that can help you in the future

getting that new reading will help

i wonder, if all else fails, perhaps look at all of your fuses in the hood and inside of the car to see if any have gone bad, and maybe if all that does not work then take it to the dealer to see what it could be, or maybe replace the ECU (they are on ebay sometimes for cheap)

but in the end my gut says the TB is at fault

[petrified.rabbit]

sound like your primary o2 sensor is taking too long to heat up, skimmed the rest, any codes ? i missed that answer.

[thehunterooo]

seems like its just a mis-firing code, which is very helpful, would that sensor cause such a rough idle?

[serega12]

ahh i read the other thread again, the car is doing this to warm up, but doing it in a poor fashion, disconnect your battery for an hour or so and reset the ECU if you have not already, thats my first guess

You could also pull the ECU fuses in the fuse panel in the driver's door jam area. Should do the same thing if you have them out for a little while. No need to wait for half hour.

[jimstolz76]

sound like your primary o2 sensor is taking too long to heat up, skimmed the rest, any codes ? i missed that answer.

p300 - random misfire. It's like searching the internet for "causes for a headache" LOL

If the O2 sensor is bad, any idea what I should be looking for? I can pull voltages from it (i think) in ScanXL but not sure what I'm looking for. Maybe i'll just set it to monitor that and try another recording today. I'm really just looking for whatever changes at that 1 minute mark when it smooths out.


Appreciate all the responses.

[petrified.rabbit]

the o2 sensor wont accurately set the fuel trims until its warmed up. the primary o2 in the aveo is heated. so it comes up to temp really fast (not sure how fast) definitely under a minute i would think.

if its not coming up to temperature as soon as it should for whatever reason, that would prolong the high idle the car has, until the o2 heats up to send a proper signal. but when the signal is in and out of range until its fully heated, the ecu could jump between o2 signal and warm up, creating a rough idle.

check the o2 signal and engine load comparatively on a scan tool and see how the coincide?

older cars used to not have heated o2 sensors, so it would be in warm up, or open loop, or preset fuel trim, longer, but as part or stricter emissions we now have heated o2 sensors to get the fuel trims matched asap.