snowleopard

Where do I start? Bought a 1995 4runner RV6 273,000k's and fell in love with it, everything seemed too good to be true until one day I went to accelerate from a set of traffic lights and what felt like someone had ploughed into the back of me with this horrific bang, but what actually happened was it slipped out of gear, it only happens on first, have tried mucking around with linkages but nothing, any ideas on what this could be? I can avoid this happening if i simply keep the stick pushed into first.

Also after coming back from a 2 week holiday I found a few oil patches below the truck, took a closer look and it looked like it was the valve gaskets so I changed them, the plenum and the pcv put it all back together and now the engine check light appears on the dash, the truck has no power after a test, went through the symtoms and it appears to be a fault with the ignition sensor, could this be the reason? Even after all this mess I went down this morning and noticed a few more leak patches and its definately not coming from the valve gaskets have checked everywhere and cannot determine the source of the leak, it appears to be running down both sides of the bottom of the engine, any suggestions? would greatly appreciate some help!