Edmunds Answers



  • karjunkie 06/30/10 8:35 am PST

    To rule out any serious internal damage, I would check the compression on each cylinder to be sure there is no burnt valves or worn piston rings. If compression is good, above 125 psi, on each cylinder, then it is likely you have a simple and inexpensive problem to fix. The random misfire codes P0300-308 are usually caused by a vacuum leak so check for any hose coming off the intake manifold that looks cracked damaged or loosly connected. This would cause the rough idle you mention. Replace the PCV valve right away as I am sure it never was changed and it can cause these problems when clogged. Easy and inexpensive to do. Finally, I strongly suggest you clean the throttle body with TB spray cleaner and also clean the EGR and IAC valves attached to the TB with the same spray. A clogged WGR or IAC valve is going to cause a rough idle too.


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