I own a 2002 Saturn with the 1.9L SOHC engine and am currently experiencing a persistent P0340 engine code. I've already replaced the spark plugs and ignition wires, but the code returns every time. What should I check next to resolve this issue? The vehicle has 179,000 miles on it and I'm looking for cost-effective solutions before considering further repairs or selling it.
I replaced the engine control module (ECM) and coil packs in addition to installing new spark plugs and wires. Since all original components were used initially, the P0340 code disappeared—but a new issue emerged: a PO301 misfire on cylinder #1. The car runs fine under load but exhibits noticeable idle hesitation. I need to pass emissions to sell it, so any advice on what to inspect next would be greatly appreciated.
First step: double-check the installation of spark plugs and wires for cylinder #1, as improper seating or damage could cause misfires.
I resolved the PO301 code by replacing the fuel injectors. When I replaced them, I also changed the fuel filter. Afterward, I received a new P0170 code. I tested fuel pressure and found it was at 55 psi—below the recommended range. Switching back to the original filter restored proper fuel pressure, and after that, all emission monitors cleared successfully with no active codes.
Refer to the trouble code section of this forum for detailed explanations of P0340 causes and fixes. Focus on checking the camshaft and crankshaft position sensors, as well as their associated circuits.