Recently I started experiencing hard start for the Isuzu Bighorn (with 4JX1 engine). I consulted my mechanic who indicated that I had contaminated diesel which I suspect happened during the last time I filled the tank. The fuel was drained and the engine behaved normally after pulling the vehicle while on gear spread 3 for a long distance. The engine started ok and I left run for three hours with a hope that the bad fuel will clear from the system.
After a month of inconsistent/troubled starting, the engine can start, but the idling is not even and sometimes it is too low. When I leave the engine to run for sometime (like 30 minutes), it stabilises, However, if I switch off the engine, the problem recurs again.
Please advice on what could be the problem.
.
Regards

George