Here's the deal. I have a 2000 Tacoma 3.4 with the 5vz-se engine. I had a couple of codes thrown from the ECU. I replaced the the Mass Air Flow sensor, The Throttle Position sensor, bought a new gas cap, plug wires, plugs, fuel filter. The truck runs an idle at around 1000 RPM but idles so rough it seems as if though it's running on just two cyclinders. The truck also tries to stall if your foot is not left on the gas pedal. I checked the truck for compression and all cyclinders were within 5 lbs. of each other. They registered at 185-190 sq.in.lbs. I can also smell raw fuel that is being dumped into the cyclinders. What would be causing this problem? The codes that were thrown were PO171,PO120,and PO450.

 

PO171 - System too lean
You probably either have leak in the fuel system or a blocked injector

PO120 - TPS malfunction
Replace TPS sensor

PO450 - Evaporative emission control malfunction

 

Yeah I replaced the TPS and MAF plus the gas cap. This truck does not have any power whats so ever. I just can't seem to get the truck to have a normal idle. I also unbolted the cat to see if I may have had alot of back pressure it didn't make a difference.

 

You might be able to smell unburnt fuel from a lean misfire (p0171) - the first thing to check would be fuel pressure, which could also cause your lack of power. If fuel pressure is low, replace the filter and recheck. If it's still low you probably have a bad fuel pump - FYI if the pressure is low and you decide to replace the pump first for some reason, replace the filter also - a clogged or restricted filter can kill a pump

 

I've replaced the fuel filter to no avail. Pretty sure pressure is good.

 

Check for vacuum leaks. Easy but not exactly the safe way to tell is to spray brake clean or ether around vacuum hoses. If the idle goes up then you've found the leak.

 

If the evap purge valve was stuck open,there could be your raw fuel smell...Also would raise idle speed ..technically its an unmetered vacuum leak...Pinch off that hose comming to the manifold from the canister...and see what happens..

 

check over your wiring harness also, sometimes when your getter multiple codes and your truck isn't running right it could be due to a bad ground

 

x2 check the ground that is on intake

When did this problem start?

 

Problem Solved!!
Here is what happened. We tried everything under the rainbow and everthing finally came down to the timing belt. The water pump had leaked coolant through the weep hole and coated the timing belt causing it to slip. Both cams were way off. The timing marks were off by one tooth. We noticed that the coolant had formed into a hard surface behind the belt and the belt was soaked with coolant. After we replaced the timing belt with a new one, lined everthing up and put the thing back together. We started it up and it purrrrs like a kitten. Thanks for everyones advice in the troubleshooting. We found the gremlin and put a hammer to em!

 

So did you replace the leaky water pump too while you were in there?

Please tell me you did.

 

appreciate the posting of the solve.

 

wow, i never would have thought that would have been the problem

 

You bet we did. The coolant that was trapped behind the timing belt was hard as a rock. There was no aluminum shavings in it either. The chunks of coolant would dislodge fall on the gears and cause the belt to actually lift off the cam gears. We used brakleen to wash the whole area out before we installed the new belt. We were suprised it would even start. The cams had to be off by at least 20-30- degrees. We think over time the belt was slowly walking on the timing gears. The brother-in-law works for a shop in Washington state. He too has never seen this happen before either. He seems to think everything was off by at least three teeth. The old belt didn't have a mark on it either. It was still really plyable, No cracks, All teeth were still on the belt.

The culprit:

 

this is why everyone should have never gone away from good old green antifreeze, it never made these big buggers. when i worked at a cadillac dealer i seen so many cars screwed up because dexcool had hardened up

 

Very interesting.

 

:thread hijack: Yeah but it helps me find exactly where the leak is coming from LOL. Find the pink crusty stuff and I know where coolant is coming from.