Miles: 209,394
Fault: P0301 misfire on cylinder 1
Preceding fault symptoms: car was running normally at idle and the stumbled momentarily only to recover. Upon starting from a cold start the next day the car had a rough idle, low power and a misfire. Upon driving to diagnose the car ran roughly, then the rough driving cleared up after 40 minutes. The fault returned upon starting the car from a cold start the next day and presented a P0301 CEL code
Steps taken:
-replaced ignition coil, plug wires and plugs with recommended NGK, no fix
-did vacuum hose visual inspection and leak test with propane, no leaks detected
-did leak test around cylinder 1 head gasket, no leaks detected
-compression tested all cylinders: 1-156, 2-160, 3-160, 4-160
-replaced fuel injector on cylinder 1, no fix
-replaced fuel pump assembly, no fix
-swapped MAF and MAP sensors, no fix
-replaced air intake junction box and throttle body assembly upon discovery that they had both been overheated and damaged, no fix
-replaced camshaft sensor, no fix
-fuel cap is new
I am really perplexed as to the problem? I keep going back to a possible intake valve issue but the compression test indicates that although cylinder one is slightly low it’s still within tolerance?
Since the cat was recently replaced I’ll replace the O2 sensors along with the crankshaft sensor since I have them but I’m not confident that this is the problem?
Does anyone have any suggestions? I am shade tree wrenching without OBD mapping?
