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1997 Chevy Pickup P0300 and P0171: Random Misfire and Lean Mixture Diagnosis

Model: 1997 Chevy pickup Fault Code: P0171 Posted: 2006-03-03 19:23

I'm having trouble diagnosing a persistent issue with my 1997 Chevrolet pickup 4.3L engine. One morning, the vehicle wouldn't start—when I pulled the spark plugs, they were wet. I replaced the spark plugs, wires, cap, and rotor. The OBD2 scanner showed two codes: P0300 (random multiple cylinder misfire) and P0171 (lean mixture in bank 1). After that, the engine stumbles both during cold starts and at highway speeds. Although the P0171 code has not reappeared, the P0300 code and stumbling behavior return intermittently. Fuel pressure is confirmed as normal. I've already replaced the coil and cleaned the MAF sensor, but the problem persists. I'm now out of common 'swap-out' components and need help identifying what else to check. Any suggestions or diagnostic steps for this 1997 Chevy pickup with P0300 and P0171 codes?

Related fault codes
P0171P0300
Comments (9)
Anonymous 2006-03-04 14:50

Check the EGR valve—common cause of misfires. Intermittent stumbles may also point to a vacuum leak around the intake manifold. These are known issues on older Chevy pickups with 4.3L engines.

Anonymous 2006-03-05 16:53

Thanks for the tip! The EGR valve is beyond my current skills, so I'll try checking for vacuum leaks using a can of ether or brake cleaner.

Anonymous 2006-03-06 10:32

For vacuum leak detection, use a propane torch (unlit) with a hose attachment to reach hard-to-access areas. Alternatively, spray ether, brake cleaner, or throttle body cleaner around the intake. When you find a leak, the idle should spike or drop noticeably. If the idle remains steady, check fuel trim values via an OBD2 scanner—this can help confirm whether there's a lean condition. Good luck and please keep us updated!

Anonymous 2006-08-25 21:30

Quick question: I was going down a hill at 985 feet and my car just didn't respond—I thought it might be related to elevation, but I'm not sure if that's relevant. My vehicle is actually a 2005 Chevy pickup, not the 1997 model mentioned in the post.

Anonymous 2006-08-26 11:28

I'm not clear on your question—could you clarify what you're asking about elevation or engine behavior?

Anonymous 2006-08-27 23:04

Bobby: If your car is still under factory warranty, consider having the dealer address the issue. Warranty coverage may cover certain mechanical failures like EGR or vacuum system problems.

Anonymous 2007-11-15 18:23

Regarding the P0300 code on my Chevy—my dealer suggested loosening the distributor and adjusting it to clear the misfire code. I'm not sure if this is a valid fix, but they claimed it resolved the issue temporarily.

Anonymous 2007-11-15 23:25

Check ignition timing and ensure the distributor is securely mounted and properly timed. A loose or incorrectly set distributor can cause intermittent misfires and poor performance on older 4.3L engines.

Anonymous 2007-11-16 08:09

Are we still discussing P0171? This behavior seems inconsistent—especially since the lean mixture code has not returned, yet symptoms persist.