Hi everyone,

I'm in need of assistance and hopefully someone can point me in the right direction. A couple weeks back my coolant was leaking near my water pump so I did a quick fix and put the coolant additive to plug the leak. At the beginning of this week I noticed a pulsing sensation when I was around 2k rpm and crusing at 60-65mpg. My check engine light would come on then go off after a couple of miles . I went to the local auto parts store and borrowed their OBDII reader and got a "Random Misfire Detected" P0300. So I looked up the code and I got a nice big list of possible items to set that code off. Here is the list I got:

Open or short in engine wire
Connector connection
Vacuum hose connector
Vacuum hose connector
Ignition system
Injector
Fuel pressure
Mass air flow meter
Engine coolant temp. sensor
Compression pressure
Valve clearance
Valve timing
PCV valve and hose
ECM

My 4runner is at 157k and the usualy timing replacement is at 160k. I was thinking of changing my timing belt, idler pulley,tensioner pulley, water pump, plugs, plug wires. Am I going in the right direction or has someone had this problem before that can tell me what I need and don't need to solve this problem? Please help me out, it would be greatly appreciated since it's my daily driver and I can almost watch the gas gauge drop.

What year model and engine?

Misfires are usually electrical in nature, so start with inspecting (and replacing if needed)the plugs, wires and coil packs.

techno hit it dead on.

And year/engine/trans details are always helpful.

Are there any indications of oil in the coolant? I hope not. I had an engine with similar symptoms, that was caused by blown head gasket. Check that MAF sensor, too.