2008 Pontiac Grand Prix codes P0300 and P0420
Asked by George Jun 18, 2020 at 06:48 PM about the 2008 Pontiac Grand Prix Base
Question type: Maintenance & Repair
Runs extremelly rough ran some fuel injector cleaner and running better but still
hesitates misfires and takes a long time to get above 30mph especially on a
hill. When first starts it wants to die unless I rev it up for about 30 sec. Any help
would be great.
4 Answers
3.8l naturally aspirated, the base model. If you push it down to the floor the rpm will go down when you let of it goes back up. It has me stumped I was thinking ecm and coils but random misfires doesnt seem to make sense with that.
Also it was getting between 21 and 24 mpg now it is getting 17 according to the computer
Clean the electronic throttle body. These engines have heavy carb build up there. Nexus Body on YT has a great video. Also make sure that your spark plugs are good.
Also based on the mileage drop, throttle body being dirty issue seems probable. However, the throttle body getting dirty is a issue that has slow onset. It usually shows up after 120km. If you have the throttle body being cleaned, get the maf sensor cleaned as well.
