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Mercedes Benz A140 P0304 Fault: Hesitation and Low Cylinder 4 Compression - Diagnosis & Repair Advice

Model: Mercedes Benz A140 Fault Code: P0304 Posted: 2011-04-28 11:54

Hi everyone, I own a 2003 Mercedes-Benz A140 (1.4L petrol, manual transmission) with the check engine light illuminated and fault code P0304. The car runs smoothly under normal conditions but exhibits a slight hesitation when stationary or during idle. I've already replaced the spark plugs, inspected fuel injectors, and checked all ignition cables. The only notable finding is low compression in cylinder 4—measured at approximately 80 psi (well below the expected range). A friend suggests that the issue may be caused by a faulty intake valve inside the engine, recommending replacement of this component. I'm seeking expert validation: Is this diagnosis plausible for my vehicle? Any insights or alternative troubleshooting steps would be greatly appreciated. Best regards, Turbo

Related fault codes

P0304

Comments (4)

Anonymous 2011-04-28 14:34

The term 'air valve' is likely a misstatement—intended to refer to the intake valve. This clarification is important for accurate diagnosis and repair.

Anonymous 2011-04-29 07:14

Thanks for the helpful correction! My name is Paul L—I currently have an A8 and am preparing for my Level 1 license. I've been following this forum for months. Though I’ve shifted careers, I still do my own vehicle repairs. Looking forward to more discussions from you all!

Anonymous 2011-04-29 07:30

Jeff Compton wrote: WTF is an air valve inside the engine? Hi! I believe he meant the intake valve. Apologies for the confusion—just a terminology mix-up. Thanks for pointing it out! Turbo

Anonymous 2011-04-29 07:49

Your friend's theory has merit. While low compression in cylinder 4 is concerning, before replacing any components, consider performing a leak-down test to confirm whether the issue stems from valve sealing or internal engine wear.