torque converter woes
Hello! I have a ’95 BMW 325i convertible with an auto tranny (GM made A4S 310R model I believe). 89,000 miles. I'm having a problem where the transmission doesn't "like" having the torque converter locked up. When I'm cruising on the highway in 4th gear (say, at 60 mph), the torque converter will normally NOT lockup, so the engine runs around 3,000 RPM. However, if I press on the gas a bit to accelerate, the torque converter locks up! Makes no sense... If I then push the throttle around halfway down, the torque converter unlocks (makes sense), and if I push further it drops to 3rd gear (also makes sense). The problem is that I would think the torque converter should be locking up when I'm cruising at highway speeds, and should unlock only when my foot comes completely off the gas or I'm asking for significant acceleration.
I spoke with a local transmission shop, and they suggested that the throttle position sensor may have a "flat spot" in the resistance measurement it sends to the computer, so the computer thinks I'm barely touching the gas and doesn't lock up the torque converter. Since this isn't a throttle-by-wire car, I thought this made a lot of sense, so I tried a new TPS sensor. No change.
I purchased this car in 2005 (66,000 mi) and changed the trans. fluid and filter back then with Redline D4 ATF. I changed it again last month to see if the torque converter behavior would change, but no luck. Has anyone noticed this with their car? Any ideas/suggestions? Thanks in advance!