Surging while cruising at 1900 RPM

[silverstreak18]

This looks suspiciously related to the OBD emissions diagnostic drive cycle software routine the ECU runs when cruising on the highway between 50-60 mph while below 3,000 rpm to test the proper functioning of the oxygen sensors. My car runs fine but I needed to do a drive cycle to get OBD readiness to pass emissions in my state since I had just reset ECU errors using MHD. (Everytime you reset errors or reset adaprations you reset OBD emissions readiness.). While doing the highway cruising portion I watched in amazement STFT1 and STFT2 cycle regularly up and down between values of 2 and 10 (IIRC). My car didn’t surge at all. RPM must have been around 2400 in 5th gear.

Mine will start swinging too, but will go negative and back up to 15 or so. I have to either be on the throttle or completely let off to go away. Throwing in the black bov spring today instead of the yellow, will see if that makes any difference.

 

[Jeffman]

My STFTs may also have dipped negative to positive during the highway stage of the drive cycle. I really don’t recall exactly. But it was a large noticeable amount.

 

[Rcboosted2007]

My STFTs may also have dipped negative to positive during the highway stage of the drive cycle. I really don’t recall exactly. But it was a large noticeable amount.

Your tune

 

[Rcboosted2007]

http://www.e90post.com/forums/showthread.php?t=1120250

 

[Jeffman]

I think you’re referring to closed loop fueling at WOT when STFTs can spike high or low depending on ones tune?
I’m referring to STFTs cycling up a down when the ECU is in its self diagnostic mode for emissions testing purposes. All US street cars go into this open loop mode regardless of tune.

 

[Rcboosted2007]

I think you’re referring to closed loop fueling at WOT when STFTs can spike high or low depending on ones tune?
I’m referring to STFTs cycling up a down when the ECU is in its self diagnostic mode for emissions testing purposes. All US street cars go into this open loop mode regardless of tune.

Whats the cause?

 

[Rcboosted2007]

Im not sure if you changed vanos solenoids yet. My car surged on freeway( pulsating power) with NO vanos codes.

 

[Jeffman]

I had gotten VANOS codes once
around 50K miles and then again at around 60K miles. Took them out, cleaned them up and switched them around when I reinstalled them. Took care of the codes each time. Maybe next time I’ll put in new ones.

Btw - I never got the pulsating power people are talking about in this thread. I was just proposing a possible source of the surging problem.