P0300 RANDOM MISFIRE

2002 TACOMA 5VZ-FE, 110k miles


My son came home from work one day and complained of :

· rough idle

· no power on acceleration and engine would choke upon acceleration until he let off the pedal

· funny rattling noise when engine is revved up at idle in park

· CEL on

Upon test driving the truck myself, all the symptoms he mentioned were there. At idle, it sounded like he had a mild racing cam on there. I pulled the code with my scan tool and got P0340 (camshaft position sensor), and P0300 (random misfire). I cleared the codes, but they returned within minutes of running the engine.

I replaced the Camshaft position sensor and the P0340 code went away, but the P0300 code remained and the truck still ran like crap. I’ve searched some of the forums and every test that I thought would solve the random misfire didn’t help.

· Changed spark plugs & wires

· Checked OHM readings on coil packs

· Switched out the coil packs, igniter, fuel injectors, & maf sensor from another Tacoma

· Changed fuel filter

· Checked fuel pressure

· Checked for vacuum leaks

· Cleaned the throttle body

· Compression test

· Seafoam in the fuel tank and straight in the intake manifold

· Took apart the ECM to see if there were any obvious burns or shorts

Nothing was helping!!!

I decided to take the timing cover off and check the timing marks. The water pump was leaking really bad and had a lot of caked up coolant around it. I set the Crank gear to TDC, and looked at the Cam gear timing marks. Sure enough, they were off! Not by a tooth or two, but the timing marks on both Cams were at about in the 2 o’clock position. The leaking water pump must have stretched out the timing belt or something.

I bought a timing belt set with tensioner, idler pulley and water pump set, did the job and slapped it back together. The truck runs like a champ again. Hope this info helps someone out.


ALOHA \m/

 

Nicely diagnosed. I always like to read when someone knows their shit and doesn't just throw parts at a problem! Good that you changed the fuel filter too, mine was so dirty I cannot believe it is marked as a lifetime part.