3.0 X Auto, 210k miles, LHD
I have been experiencing hard shifting for several days now, mostly between gears 2-3 and 3-4. It's different out of sport mode-- can't articulate it clearly, but maybe less of a delay in sport mode but a harder jerk. This difference, however vague, made me think initially this is an electronic issue.
I drive a lot on dirt roads, and wash the car frequently- this is relevant because at first I suspected I had rattled something important into oblivion within the gearbox, then perhaps more likely loosened a sensor. I also later realized this started happening right after I washed the car, which has a known water leak behind the glove box.
I had the car scanned at AAMCO and had a long list of codes, many relating to electrical, but those related to the trans were P0706, P1780, and P1573 (throttle angle error). They assured me my trans was probably fine and that it sounded like a throttle position sensor (TPS) or transmission control module (TCM) issue. Regardless of what Jabba at AAMCO told me, aside from the helpful codes they gave, I read through this forum to see what others have experienced...

Here's what I've checked so far.

1.Removed the TCM on the driver's side.No evidence of moisture on that side, connections fine, circuit board looked brand new.
--Ordered 5-point torx security bits to make the next two parts easier--
2. Removed ECU plug on back left of engine bay, found no evidence of moisture entry. Cleaned with CRC spray and dielectric grease, reassembled.
3. Removed and cleaned throttle body (was very nasty, never removed before). Removed TPS and carefully sprayed with air compressor and tested movement. Visually and mechanically fine. Did not remove metal housing to check contact/tracks, nor did I check resistance or anything electronic (could maybe try with guidance). Found the 2-way plug on TB was entirely eroded away... wires still connectable.Cleaned and taped well for now.
4. Removed gas pedal and its attached module. Opened and inspected, the tracks and wipers looked fine, nothing bent.
5. Drained and added trans fluid twice during all of this.

Cleaning the TB has smoothed the idle and perhaps freed up some power, but the main issue of the hard shifting is still there. Sometimes it shifts all the way to 5 smooth as butter, but the jerky shift is always back soon. I have been driving very carefully since I noticed this, and can't correlate any particular input on my end that causes or prevents the hard shifts. I don't get "limp home" mode or a dash full of lights. Check engine light is not on right now (comes and goes due to a failing cat for the last 100k miles). Everything else about how the car drives seems perfect.

What I am thinking is:

1. TPS could be bad, since I only checked the shell. Anyone had luck with an aftermarket $12 TPS from eBay? (So many of the older threads on this topic lament the TPS being unserviceable and having to buy a whole new TB for $500-900... there are now TPSs for $12 and new TBs for $200 or less)

2. Based on S-Types, I have a clue to check the J-Gate and its sensors, though I'm not exactly sure what to look for.

3. Neutral safety switch on top of gearbox?

Agree or disagree? These issues are all new to me. I'm asking for any tips on what this could be or what to test next, or perhaps something I missed. Thank you very much!

 

I should add that I have owned the car for a decade and driven most of those miles myself, and this issue is entirely new. I have seen the car through many of the typical trans issues at this life stage that many others have experienced, and changed the fluid a couple handfuls of times over the years to find any mild slipping disappear. In this case, it is not slipping, just jerking into gear.

I understand how sport mode works, so I guess what caught my attention was not that it shifted harder, but the manner in which it shifted hard was different. Again, hard to explain, maybe irrelevant, probably a function of whatever is causing this.

For further introduction, I am in Southern California and the car is a workhorse. I don't baby it. I drive the vehicle hard (dirt roads, LA traffic, almost daily mountain descents/ascents) but not the engine/trans, which I almost never lay into.

Thanks again for your time! I hope by sharing this troubleshooting it will help someone else experiencing something similar.