Herm

About one week after I replaced the starter on my 1993 LS 400 (150,000 miles), the engine light came on with error code 25 and 26 (fuel mixture rich/lean), it went out on it's own, the code was stored in memory.

I cleared the memory but the engine light came on again with code 25 after about another week of driving every day.

Any common causes for this error ? Since the problem started about a week aftetr I had the whole top of the engine off I'm afraid there may be an intermittant connector somewhere

19psi

check your vacuum lines. those old lines are brittle and can crack easily and you won't even know. a cracked vac. line will cause codes like you have. get some carb cleaner and lightly spray the upper intake area or wherever you took off vac lines while hte engine is running. if you have a leak, the engine will change sound and speed when the spray hits the leak.