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I have a 2003 cadillac deville and for the past two weeks i have had a p0300 code. I have pretty much all new parts in this car and im tired of trying to guess what its problem is. At idle, the car jerks /stumbles. When put in gear, seems to get worse. Have checked for vacumn leaks, new coils, new plugs, clean egr, replaced plenum duct, cleaned maf sensor, cleaned throttle body, new map sensor, cleaned iac, new tps, new cat, i really dont know what else to do. The car also jerks when trying to pick up more speed and seems to struggle. Any help will be appreciated. Engine light flashes sometimes.
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Try checking more internal like a head gasket. Try a leakdown test and a compression test. Maybe you are losing compression in a cylinder causing the random misfire.
When the engine light flashes, at least on my vehicle, there are multiple misfires occurring and loss of power. If you got the P0300 code using a scanner with bi directional control you may be able to check each fuel injector by disabling them 1 at a time to find out which cylinders are misfiring. If you just have a code reader then you won’t be able to do this check.
Just a little update. I notice that the symptoms are not as bad when the ac is off. Also when the ac is on, at the time i get the jerking, i also get a chirping sound from the passenger side under the hood. Ses light flashes but does not stay on. Also tried new cam sensor.
The P0300 is a general misfire code and your symptoms go along with that. The light flashes when it detects a misfire that’s severe enough to damage the catalytic converter or other engine components. The fact that it’s severe might make it easier to track down. As pointed out above I think a power balance test might be a good start because it can help nail down the offending cylinder(s). Once you’ve found them then you can check to see if you have a mixture problem such as a vacuum leak, an ignition problem (however you mentioned new plugs), or a mechanical issue. Don’t rule out a mechanical issue. Unfortunately the Northstar engine is prone to head gasket issues. If you DO find that to be the case know that you can’t just replace the gaskets. You also need to drill out the head bolt holes and install new thread inserts, if not the problem is likely to come back due to the head bolts pulling the threads right out of the block causing a loss of tension on the gasket.
Good luck and keep us posted.
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