P0740 What do I do?

[Ellipsis]

My 2000 S70 2.4L NA, 5 speed auto, 169,000 miles, keeps intermittently throwing code P0740 (Torque converter clutch circuit/open). It also throws code P1618, which I understand is a sympathetic code. When it does this, it will not drop below 3rd gear, making acceleration very slow. The only way to make it act normal again is to clear the codes. It will also often jerk while accelerating, even when these codes are not present. Most of my research has shown that this is a bad solenoid, but some say that it may just be a speed sensor (see: http://www.volvo-forums.com/t23073-tran ... p-mode.htm ), while others say it might be a bad torque converter. Any thoughts? What are the chances it's just a speed sensor? Thanks.