Weird throttle issue H6-3.0

[Ken2004LLBean]

I've been having driveability issues and a persistent CEL since an engine swap (see link to main thread below).  I noticed a weird thing while driving the car and monitoring live data.  When I am maintaining speed, or slightly accelerating, and then release the throttle (either to come to a stop, or reduce speed), I noticed the car goes from closed loop, to open loop, and it bucks for a second (feels like a downshift - I have an automatic trans).  Then, it goes back to closed loop after a second or so. It does this at local road speeds, and highway speeds, although if I let off the throttle at highway speeds, it does not revert to closed loop on its own; it stays in OL until I press on the throttle again.

I have had surging idle speeds, and also surging when coming off-idle from a stop, and every time the engine hunts/surges in rpms, the car has been in open loop.

Also, a few times while maintaining speed on local roads, when the rpm is around 1,500, I have felt the car losing power briefly (engine power, not electrical power).  This is when I am barely touching the throttle, so it's at or near its lowest position.

I have been trying to establish any patterns, and as far as I can tell, although I'm not 100 percent sure, it doesn't seem to be dependent on or affected by road speed, engine speed (rpm), engine temperature, ambient temperature.  The one common denominator for when the car goes into open loop/surges/bucks seems to be throttle position.  It acts up right around the lower edge of throttle position.

My simple live data scanner records throttle position at 13.7 percent when fully closed, and about 80 percent when fully open.  The car acts up in the 14 percent throttle position range.  It doesn't happen 100 percent of the time, but probably 80 percent of the time. It's a very annoying phenomenon.

The TPS is a brand-new OEM part purchased from the dealer. I have a second TPS that is also fairly new, which was installed by a mechanic when I was having wild idle surges.  I have tried switching both TPS back and forth, but have the same issues with both.

Unlike the H4 engines, the TPS on H6 engines is not adjustable.  There was a TSB on the throttle position sensors on the 2001-2004 H6 3.0 Outbacks, but the part I bought from the dealer is the new-and-improved TPS.  Still, I suppose it could be defective.

I find it odd that this TPS doesn't show full range of throttle opening percentages (i.e., 0-100%).  The one on the car now goes from 13.7 to 80 percent.  My other one goes from 14.1 percent to about 81 percent.  I took readings on a different H6 Outback (also a 2004), and its TPS read from 11.1 percent to 85 percent.

Mainly, though, I am curious: What would cause a warmed-up engine to go from closed loop, back to open loop? Is it normal for it to go into open loop when letting off the throttle? Can anyone with a 2001-2004 H6 3.0 Outback and access to live data while driving check on this to see if it happens with your vehicle?

-Ken

 

 

 

 

 

 

 

 

 

 

Edited April 7, 2019 by Ken2004LLBean
add info

[Ken2004LLBean]

Perhaps also worth mentioning: When I have key on, engine off, and activate the throttle, I can hear a solenoid inside the transmission pan humming/buzzing, and the more I push the pedal, the louder it buzzes.  I tried this with another '04 H6 car, and it did the same thing, and from what I've read, this is normal.

The mechanic did replace a solenoid in the transmission (described in the invoice as "solenoid B") following the engine swap, when the car did not shift properly.  The car shifted properly since.

So apparently, the TPS must send a signal directly to a solenoid in the transmission, which leads me to wonder if this going into open loop/bucking thing is a transmission-related issue?  My scanner can only read the ECM, not the TCM, but the transmission light does not flash, like it did before the mechanic replaced the transmission solenoid.  (BTW, I have checked and verified that the transmission fluid level is full.)