A idle air control valve won't cause engine miss fire codes.Seems like the miss fires are on all the same back and with it only being at idle I would suspect a vacuum leak.So how did you look for a vacuum leak?

Just looked visually for vacuum leaks is there a better way...?

You feel quite certain it would not be the timing belt being out of time causing three misfires.... And is there a definitive way to make sure it is not the timing belt (it is only 5000 miles old)

Thanks Rolfe

If one of the cam timings on that that bank of cylinders jumped it could cause miss fires at idle and not while driving. You would have to pull the timing cover and line the marks up to check that. I would rule other things out first though.The best way is to use a smoke test to find vacuum leaks.Then second best way is a scan tool that reads live data while watching the fuel trims and spraying carb spray. The third best is let it idle get some carb spray spray around All the vacuum lines vacuum sources and intake manifold and gasket.If the rpms go up down or stumbles stalls etc you found a leak.

I will try out your vacuum leak advice....
You feel a vacuum leak could cause misfiring in only three cylinders one – three – five..?

You would say after vacuum looks good. The next step would be to check the timing belt...
Wouldn't it be rare for a 5000 mile timing belt to jump...?
Could the tensioner be bad. It was also replaced...?
Thank you Rolfe

Let's try the vacuum leak and go from I doubt a new belt and tenisor jumpped if it was installed correctly.