Have 1990 Montero,replaced computer fixed engine light problem,but I am getting a scraping noise from drivers side vale cover,mechanic told me its the timing belt just this make sense.

The timing belt is not under the valve cover. It's behind the plastic covers on the front of the engine. If the scraping noise sounds like rubber, maybe it's the timing belt.... if it sounds like metal on metal, it's something else. Try removing the oil fill cap on the driver side valve cover to see if the noise is from inside the valve cover. To check for a frayed timing belt, remove the black plastic cam sprocket cover in front of the driver side valve cover, start the engine and watch the belt at idle. If the belt is frayed, change it very, very soon.

Frank

Woo, I was right on the ECU thing. Yeah, like Frank said, remove the plastic timing cover on the driverside. That is the easiest. Just 2 10mm head bolts. Could it possibly be the idler pulley bearings? Are all the belts tight?