Code P0300, no throttle past 1,500 RPMs?

  • 2.0L
  • 4 CYL
  • 170,000 MILES
Car has p0300 and when you press on accelerator pedal it will rev up to 1,500, but stops there like a rev limiter almost, occasionally stalls when let off accelerator completely, sometimes will go to 3,000 RPMs at first but then slowly drops.
Misfires are about even across all cylinders.
New plugs, a couple of new coils.
Disconnect MAF car runs the same try substituting MAF with known good did not work.
Pcv valve is new.
Intake manifold is new with runners and they do move.
Throttle body moves as it should isn’t dirty and seems to be within spec.
Under smoke test we get some smoke from PCV housing and a small hose under intake, but they’re pretty small, I don’t think they’re problem.
High pressure fuel pid is at spec on live data.
There is also a broken wastegate solenoid one of the air hoses but it looks to have been that way a long time the hose was just sitting customer made it Sound like one day no throttle response, so I plugged the solenoid hole doesn’t leak air for testing purposes.
What else should I look for?
Are small air leaks enough to limit RPMs like that? The misfires get worse with load, at idle there are none.
Saturday, April 8th, 2023 AT 3:21 PM

1 Reply

  • 44,365 POSTS
Let's remove the spark plugs to see what they look like, if there are black, I would check for exhaust system blockage. Replace the spark plugs with new at the correct gap. Here is a guide to help you check the system and I would remove the exhaust headpipe to see if that fixes the problem.

You can use a vacuum gauge and snap the throttle to see if the vacuum recovers quickly. Please go over this guide and report back. Unload images of the spark plugs as well.
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Monday, April 10th, 2023 AT 9:46 AM

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