I have a 2003 GMC Envoy SLT and I just had all 6 spark plugs and ignition coils changed -brand new- and the truck is running rough. I took it to AutoZone to check the codes and it sates that its the fuel injector. The sales guy suggested that I use Sea Foam Motor Treatment and run the vehicle for a few days to see if there is any trash in the gas tank to clear out. My only concern is that the Check Engine light is blinking when I apply speed. I know that that must be a bad sign. What can this be?

 

Yeah do not drive it if the CEL is flashing . You should probably have it towed to the shop . did he tell you the codes ? I would go back thru your plug and coil work . Sometimes these coil on plug setups do not sit on the plug correctly and can cause issues like you are seeing. If you did not see this issue before you changed them I would go back o9ver that before having it towed but dont drive it if it flashing , you run the risk of possibly ruining the cat .