Why Engine looses power at stop or red light stops?

A diagnostic tool should be able to retrieve any trouble codes -- there may be some even with no warning light on. Codes could give you clues on where to direct your attention to resolve the concern. Since restarting the vehicle seems to correct the concern temporarily, it would seem that this should be something troubleshooting can pick up while the problem occurs. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops