Try checking air vacuum connections, particularly the EGR plastic box (odd shaped) and the connection where intake air comes to meet the manifold throttle body. For example, in my 98 LS400 one of the many times I removed the big black piece connecting to throttle body manifold (near center of engine bay) ; I didn't make the rubber and hose clamp perfectly 100% and I had random things happen very briefly and intermittently. These events were: VSC off warning light, check engine warning, randomized low acceleration power, and most importantly - extreme automatic transmission gear change. Hope this helps!