[darwood]

I'll share my experience of an issue I just had with my STi.

About 2 weeks ago when the car was warmed up the rpm's would surge about +-500 rpm's from where the throttle was set. So if I was running at 3000 rpm's the car would surge from 3500 rpm's to 2500 rpm's. Now this occurred while in neutral or gear. This also caused a nauseating drive since there was the constant acceleration followed by acceleration.

This behavior also subsided while rapidly accelerating but of course came back as soon as I maintained a constant throttle. Based on these observations I thought it might be the O2 sensor doing whacky things. Since the car seemed fine when it should have been in open loop mode, but as soon as it went closed loop it didn't run so well.

I took it into the dealer and the replaced the "air fuel ratio sensor" and the problem went away.

Now I also have a question. What the heck is the "air fuel ratio sensor"? As far as I know the O2 sensor is what determines what the ratio is and adjusts accordingly. Is this some new type of sensor or is it a fancy name for the O2 sensor.

[Singletrack]

Originally Posted by darwood

I'll share my experience of an issue I just had with my STi.

About 2 weeks ago when the car was warmed up the rpm's would surge about +-500 rpm's from where the throttle was set. So if I was running at 3000 rpm's the car would surge from 3500 rpm's to 2500 rpm's. Now this occurred while in neutral or gear. This also caused a nauseating drive since there was the constant acceleration followed by acceleration.

This behavior also subsided while rapidly accelerating but of course came back as soon as I maintained a constant throttle. Based on these observations I thought it might be the O2 sensor doing whacky things. Since the car seemed fine when it should have been in open loop mode, but as soon as it went closed loop it didn't run so well.

I took it into the dealer and the replaced the "air fuel ratio sensor" and the problem went away.

Now I also have a question. What the heck is the "air fuel ratio sensor"? As far as I know the O2 sensor is what determines what the ratio is and adjusts accordingly. Is this some new type of sensor or is it a fancy name for the O2 sensor.

The 02 sensor is what determines A/F ratio so more than likely the guy just used the wrong terminology.

-st

[darwood]

That's what I was starting to suspect. Funny thing is when I took it in I said that it probably was the O2 sensor. I think the service rep also mistook the wastegate sound as the motor misfiring since that's what he wrote on his writeup when I brought it in. I don't really know why he thought it was misfiring. I was less than impressed with the guy.