406oc.co.uk

While trying to diagnose a weird braking fault I have I think I've made my 406 lose power. Sound like turbo loss from reading other posts. I was checking vac circuit which included the two solenoids EGR and turbo valve I believe. I also changed the air filter as it wasnt done in a while. Way I see it I've upset either of the following ECU, vacuum solenoid valves or possibly air sensor when changing filter. I'm getting no warning lights. Any tip on what to do to diagnose? Does no warning light mean no error codes to read?

Mike