Rough Idle And Engine Off In Waiting

[awze]

I have read this forum a few times before, but never post a thread. I would appreciate anyone can provide help with my problem.

My 94 LS400 now is just about 120000km because I drive another car in the winter. The car is very well maintained and has no big problem before. But last year it got a problem when the gas price in the summer of 2008 in Canada hit $1.38/litre for regular. I filled up with premium gas ($1.5/L) from an Esso gas station in North York, Toronto. Just out of thte gas station about 10 meters, my car engine went off first time when moving and it went off about more than a dozen times during my driving back to home about 40km. Two times happned in waiting the traffic. The engine could be restarted immidiately. I though the gas had problem, so I bought one can of Sea Foam put it into gas tank and run out the most gas filled from Esso on a long highway drive. The problem was disappeared. The car was running smoothly like before. After about two weeks, the CHECK engine light and TRAC OFF light came on when I was driving. It sometimes went off, but it would come up again sometimes when driving fast on highway. I went to my mechnic and they told me the fuel line regulator malfunction. So they replaced using Toyoto part, but the CHECK engine and TRAC OFF still com up after driving more than half hour, then it developed very rough idle and engine sometimes goes off for suddenly low rpm while waiting in traffic. The CHECK engine and TRAC OFF, and rough idle won't come up every moring in the first harf hour my driving. It looks like the problem is not come up in cool weather. I droved one night to airport and it didn't have the problem on whole trip.

When first time the CHECK engine and TRAC OFF came up, I got the engine check code 25. But I got Code 25 and Code 31 on recently check engine. I got all four oxygen sensors replaced today with Denso sensors, but the rough idle and engine off problem seems get worse.

I am stucked here and hope anyone can give me some clues.