Chasing down low power/ stumble problem

Hello all, I have been reading threads on here for a while and decided to join.
Alright, here goes:
I bought a 2002 Tacoma 3.4 (156,000 miles) back in November. Shortly after, the engine light came on. PO300, PO303, PO306. Turns out, it was a bad ignition coil, so I changed it as well as spark plugs (the double tipped kind as recommended) and wires. I still had a problem with what appears to be a flooding issue at a cold startup. You go to give it gas and it bogs down for about 30 seconds and then clears up. Also, it has a low power condition as highway speeds. It won't hold a hill, and when it goes to passing gear, it maintains speed but does not accelerate. Every now and then when you quickly press the gas pedal, it will stumble for a split second. I checked the mass air flow readings and had 87 grams per second, which was within range. So, I thought the converter could be bad due to the bad coil so I had them checked. The front one was bad. I changed it yesterday to no avail. Now I guess I have to start throwing more parts at it. The check engine light has not came on since the coil change. Clean air filter, good oil. Shifts well. Any help would be appreciated!

 

If its stumbling under load and you're having problems with power, my first guess would be the fuel filter. If its missing from insufficient fuel, the knock sensor could automatically retard the timing to the max value and cause your poor performance. A fuel filter is where I would start. As far as flooding, how does your fuel consumption compare to normal? If you're really dumping fuel, yes, it could obstruct the cat and also cause a lack of power (which you could verify by dropping the cat to take a look). Or, you could drop the cat and give it a short drive to see if the power returns (not too long else you risk burning the exhaust valves from lack of back pressure).

 

I'm sorry. I left that part out. It has a new fuel filter. I already changed the cat. No change in symptoms. Fuel consumption is about 11 MPG highway. The mechanic seems to think it is the mass airflow sensor. It is reading 86.5 grams/second to a target of 87, which I thought was ok, but who knows. The dealership I bought it from is sending me a check for a new one. I should have it within a week or so. Also, I have to put new valve cover gaskets on it, but that shouldn't affect performance according to the mechanic.

 

P0300 is random misfire
P0303 is cyl 3 misfire
P0306 is cyl 6 misfire

Both cylinders are on the back of the engine.
Check all the wiring back there, and going back there, check the plugs, they could have a crack. Rule out all the free stuff.

 

I looked at the drawings and cylinder numbers and #3 is (looking at front) middle left. 6 is right rear. After I changed the coil, that problem went away. I Believe the truck had multiple problems when purchased. I pulled the new plugs out after 1000 miles and they looked great. No carbon tracking or cracks. I also turned out the lights and looked for sparks from the new wires and they looked good. Hopefully a MAF will straighten it out. I ordered one yesterday from rock auto. Love those guys!

 

Update. I put a brand new MAF sensor and still no change. I am taking it to a mechanic tomorrow probably. Guess I will have to bite the bullet and pay up. I am willing to bet it is a fuel delivery issue. Bad regulator (too much fuel) or bad fuel pump (too little fuel). Almost seems like too much fuel. Who knows at this point.

 

Another update. The truck is driving the mechanic crazy. He checked the fuel system. Good pressure throughout. Good filter. He checked the timing and it was dead on. Cam sensor is ok. Crank sensor is ok. He said it was running rich and the computer is trying to lean it out. He pulled the exhaust off from in front of the 1st cat. No change. He seems to think the exhaust is clogged in the manifold or crossover. I guess he is going to try to get it off and see what happens. He has had it for almost 2 weeks. Ill keep you guys posted.

 

I am having similar issues and about out of ideas....

 

Engine coolant temperature sensor? If it dies, it may fail where it indicates your coolant is cold, thus flooding the truck...however, the codes seem to contradict that thought. ECTs are cheap though.

 

I'm gonna guess... the EGR Valve is stuck open or closed.

 

I got it fixed! ! After 3 mechanics and 3 months of trial and error, the Toyota dealership found it. They started out by checking the timing and the mechanic saw the harmonic balancer wobbling. After further inspection, ALL of the pullies were loose and moving back and forth on the crank shaft. Someone had changed the timing belt and they didn't install the key back properly. This caused the key way to become loose. The end result was the crank position sensor was about 15 degrees BEHIND top dead center due to the loose pulley. The computer picked up the signal and retarded the electronic timing. The mechanic changed the crank pulley, Idler pulley, tensioner pulley, front main seal, timing belt, all the drive belts, and changed the oil all for $1,100. I saved a lot on labor because they already had the parts off. This truck runs like a DREAM now. I can't even feel the engine running. I hope this helps someone and restores some faith in the dealerships. I got the work done at Reinhardt Toyota in Montgomery Alabama. Thank you all for the help!!