Random Missfire

[Shipe12]

Hi i have a 99 GST and i have a random multiple missfire code i have replaced everything but the coil packs. In the diagnostics it says you could have a vaccum leak thats causing the missfire. Could a missfire cause the car to run at a lower In Hg or do i have a vaccum leak for sure, because my car idles at 10-15 In hg. thanks for any help.

 

[T is for TURBO]

Man, I don't remember what idle vacuum should be... but for some reason, I think it should be about 18 with stock cams. So a vacuum leak could be the culprit. Also, your CAM sensor could be shot.

 

[DSM-sagacious]

If its a vacuum leak you can find it with a boost leak test.

 

[PieEyedPiper]

Is this a P0300?

If so search for that CEL and you'll find plenty on the topic. From my experience, you'd be lucky if it was ignition related.