Erratic idle sometimes

Hi,

 

Every now and then I get a strange idle condition where the revs rise to say 1200 then drop to say 500 until eventually she idles steady at around 800rpm. Goes up and down say 6 times before stabilizing. I've checked all the rough idle threads and the causes can be many. I'm not throwing any codes.

 

Just wondering if this could be an oxygen sensor (front and or rear) and the best way to test these. Also, what role does the rear 02 sensor play?

 

Thanks !!

Attached is a log of my crazy idle and one at cruise. Can anyone please guess as to what may be going on here?

Crazy_idle_20100223.pdf

Cruise.pdf

I don't know much, but it looks like it's time for a new front afr sensor for you. Either that or something else is causing your fueling to be all over the place. I obviously am not an expert

Hi,

 

Every now and then I get a strange idle condition where the revs rise to say 1200 then drop to say 500 until eventually she idles steady at around 800rpm. Goes up and down say 6 times before stabilizing. I've checked all the rough idle threads and the causes can be many. I'm not throwing any codes.

 

Just wondering if this could be an oxygen sensor (front and or rear) and the best way to test these. Also, what role does the rear 02 sensor play?

 

Thanks !!

 

Dont know if it makes a difference but do you have a manual or auto? Something like this was happening every so often with my 05 2.5rs (5-spd) It would happen when coasting with the clutch in. The idle would bounce like you describe until i stopped. If i would coast without pushing in the clutch it wouldn't happen. The dealer could never replicate it.

Yeah, a bit crazy hey. I do have a 5 speed and have noticed before this problem the clutch in coasting issue. Does the ECU look at clutch engagement !?

 

I plan to give it a sea foam treatment in case it is just crud buildup as the car now only does short trips. Failing that, I'll replace the o2 sensors ($$$$) then take it to a dealer if still issues

Actually I take back what I said. Both your front and rear AFR logged values are consistent with each other. So I don't know what it is. Sorry again. I still don't know much, but I think the values you're logging are a combination of useless and not completing the picture. Try:

1. rpm

2. engine load direct (not calculated)

3. ignition total timing

4. manifold relative pressure (psi) (corrected)

5. Mass airflow g/s

6. knock sum

7. primary wastegate duty cycle (%)

8. throttle opening angle

 

Could be something as simple as a vacuum leak, but not enough info to tell. I really don't know anything though

Thanks ClimberD, will do and post tomorrw.

ClimberD attached is the log.

 

What seems very strange (to me anyway) is the igintion timing. It seems to be all over the place. High when the revs dip and low when the revs rise. Is this just a symptom ?? What could be causing this??

erratic_idle_romraiderlog_20100225_190346.csv

wow that is an absolute mess. Tons of knock according to your ECU. I just don't have the experience or knowledge to tell you what's going on, but I suggest you PM someone who knows how to interpret logs, like Infamous 1, and see if that gets you something. Either something loose is tapping/rattling around against your engine at idle and tripping your knock sensor, causing your ECU to think it's knocking, or, it's really knocking a lot and you need to fix something ASAP. Don't be shy, and good luck. Can you get a log of when you are accelerating (if you're driving it anyways)? Good luck with this.

 

BTW have you posted this on RomRaider.com? those guys might be more receptive.

Thanks ClimberD. Yeah, maybe something is tapping? On power runs knock levels seem to be fine. Thing is though, I have a knock link and don't see any knocks. I wonder if my knock sensor is fried. I will take your advise and post on romraider.

Thanks ClimberD. Yeah, maybe something is tapping? On power runs knock levels seem to be fine. Thing is though, I have a knock link and don't see any knocks. I wonder if my knock sensor is fried. I will take your advise and post on romraider.

 

If your knock link is calibrated right (I only know how the TurboXS one works, off of the stock knock sensor...) then that would be a very good place to look. Do you have a second knock sensor that is in a different place than the OEM one? Might be your answer. I just don't want to guide you wrong with your money on the line...

Yeah, I have a knock link that is separate to the standard one and is configured on most sensitive setting. I may try to simulate the timing issue by tapping the engine whilst it is at idle and see if the revs drop.