1997 Chevy K1500 P0300 and P0100 Codes: Rough Idle, Hard Start, and Misfire Diagnosis
I own a 1997 Chevrolet K1500 and am currently struggling with persistent engine issues. The truck started exhibiting a rough idle, which led me to replace the spark plugs—this did not resolve the problem. The check engine light would come on and off intermittently. After replacing the exhaust converter (which was found faulty), the idle improved slightly but starting became difficult. A month later, I noticed the muffler was failing and replaced it. However, the check engine light remained on. A diagnostic scan revealed P0300 (Random/Multiple Cylinder Misfire Detected) and later also P0100 (Mass or Volume Air Flow Circuit Malfunction). I replaced the distributor cap, rotor, spark plug wires, and coil pack. Unfortunately, the rough idle worsened. I pulled all spark plugs again and found that cylinder #5 was wet while others were dry. After removing and replacing cylinder #5’s plug, the issue persisted. I tried using injector cleaner with no improvement. Upon rechecking cylinder #5, the plug was now dry but showed a slight rich condition—indicating it was firing. I took the truck to a shop for further evaluation. They confirmed both P0300 and P0100 codes during diagnostics. I’m at a loss as to what’s causing this. Any insights or troubleshooting steps would be greatly appreciated. Mike
Let's break down the trouble codes first: - P0300: Random/Multiple Cylinder Misfire Detected - P0100: Mass or Volume Air Flow Circuit Malfunction If you're certain all cylinders are receiving proper spark—especially cylinder #5, which previously had a wet plug—then components like spark plugs, wires, coil, distributor cap, and rotor can be ruled out. Given that cylinder #5 was initially wet but now shows normal (though slightly rich) readings with firing confirmed, it strongly suggests a leaking fuel injector in cylinder #5. Excess fuel could have caused overheating of the converter and muffler, which may explain their failure. I recommend replacing the fuel injector on cylinder #5 immediately. A compression test is also advised to rule out mechanical issues. The P0100 code indicates a potential MAF sensor issue—this should be addressed as well. However, start by checking for vacuum leaks in hoses and intake manifold (a common cause of these symptoms). Also inspect all electrical connections under the hood for looseness or corrosion. Note: The MAF error may have been triggered by excess fuel from cylinder #5. Therefore, fix cylinder #5 first. After replacement, reset the codes and monitor idle behavior. If the issue persists, investigate vacuum leaks and then consider cleaning or replacing the MAF sensor. For more details on these codes, refer to: https://www.obd-codes.com/trouble_codes/p0100.php Trouble codes provide limited insight—using an OBD2 scanner connected to a laptop or mechanic’s diagnostic tool is essential for accurate diagnosis.