I have a 1994 GMC Safari and it cranks but will not start. The repair shop found the valve stuck open and said they cleaned the carbon out of it. 2 days latter, it will not start again. The shop said I should just replace the valve. Before I spend $200 for the part, I want to make sure this is the actual problem. I know the EGR can cause rough running, but will it cause the car to just crank and not start?