My 89 toyota is throwing a code 25 which is a lean air fuel mixture, I was wondering if this is a common problem and which is the best steps to diagnose the cause seeing how the book says it could be a number of things, when the truck is cold it idles high but runs strong, the warmer it gets it idles lower to the point of almost dying at a stop light if I were to run wide open and just take the truck out of gear it idles extremely low, I can down shift through the gears and it will usually be idling fine when I stop any info on this is greatly appreciated