Lock Up Complaint: Issue 52, page 39, offered an in-depth look at torque converter lock-up. Although the author was specifically talking about the '98.5 and newer trucks, this tip applies to torque converter lock-up on Turbo Diesels '94 and later.
As documented, many people have replaced the TPS or APPS, transmission temperature sensor and numerous other parts trying to correct the ongoing converter clutch problem with varying degrees of success.
Well, for all of the shadetree mechanics in Turbo Diesel land, before replacing any parts or wasting time connecting a scan tool or voltmeter to the electrical circuit, start with the easiest step first.
I have found the cause of the lock-unlock problem to be a frequency-induced electrical noise into the ground circuit of the battery which causes a fluctuating voltage signal from the TPS to the PCM.
The Solution: Locate the 10-gauge ground wire that runs from the negative post of the passenger battery to the back of the alternator. This wire is often tan with a black stripe.
Starting at the back of the alternator loom where the tan/black striped wire heads for the battery, wrap the wire with a piece of tin foil about 4" - 6" in length. Wrap the tin foil with black electrical tape to secure it in place.
Road test the vehicle. If the problem is corrected, smile.