Starter Problems/IAC/Evap(?)

toyota
tundra

#1

I have a 2003 Toyota Tundra v6 that starts up just fine when it’s cold but not after it’s warmed up. After it’s warmed up it will crank and not turn over. When this happens, I have to give it gas while starting to get it to turn over. Or, if I turn the key to the on position and wait about 10 to 15 seconds it will start. I suspected it might be an IAC issue but after taking it to Autozone, they hooked it up to a code reader and it indicated a P0456 issue. The check engine light has not come on for this. Sometimes, I can also smell gas when I have to step on the gas pedal to start it up (makes sense actually)…but I have also smelled gas after turning the vehicle off after driving it. This smell comes from under the hood. Any idea on what could be the culprit? Could it be as simple as a bad gas cap? Thanks in advance.


#2

The DTC P0456 indicates a very small leak in the EVAP system.

That could be the reason you’re smelling a gas odor. But that wouldn’t prevent the engine from starting.

Turning the ignition on for 10-15 seconds wouldn’t solve the problem because the fuel pump only runs for a second or two and then shuts off when the ignition is turned to on.

The problem is most likely with the IAC valve.

The IAC valve controls the engines idle under all conditions. Including when starting the engine.

If the IAC valve is failing to allow air into the engine when attempting to start it, the engine won’t start. But as soon as you step on the gas pedal, this opens the throttle plate. This allows air into the engine and it starts.

A faulty IAC valve usually won’t turn on the Check Engine light because it’s an engine control device. And not an emission control device.

Tester


#3

Another idea, the engine is flooded for some reason. That would explain why it won’t start when hot, and why pushing your foot on the gas pedal helps get it to start when hot. When you push your foot on the pedal, all that does is open the throttle valve so more air goes in. Which would balance out too much fuel.

  • You may have a fuel injector which leaks fuel into the intake manifold when the engine is turned off. A fuel pressure test is one way to check to see if the fuel rail pressure is holding or not with the engine turned off.

  • Purge problems in the evap system can sometimes cause overly rich operation.


#4

So would it be a canister issue under the truck or under the hood? So many places to go with this…if it was a fuel injection leak, why would it be able to start without a problem when it’s cold? And is there something about the gas agitation that could cause excess pressure on the evaporate system causing a small flooding of fumes into the air intake(?)…maybe? I’m trying to wrap my mind around this without spending a fortune on replacing parts that don’t need to be. The only code the engine is throwing is the 0456. So that seems to be the main culprit. Damn I don’t know.


#5

I used a Lucas Complete Engine Treatment additive to a full tank of fuel yesterday and today (85 miles in) it hasn’t had the issue. Starts up just fine hot or cold and faster than before (less cranking). Could my issue have been a dirty fuel injector?


#6

The canister is usually in the engine compartment. The problem wouldn’t usually be the canister itself, but the purge valve.

If the injector was slowly leaking gas into the engine when the engine was off, that would make for a very rich mixture on the next start. But a rich mixture is exactly what is needed for a cold engine to start. But an overly rich mixture could prevent a warm engine from starting. Ask me how I know this … lol …

No. But pressure can develop in the evap system when the temperature in the fuel tank rises. What’s supposed to happen in that case is the developing pressure drives gas vapors into the canister, which holds onto the gas but allows clean air to exit. When all that works, the pressure doesn’t get too high.

Yes.


#7

Depends on the vehicle

I’d say a canister is just as likely to be underneath a vehicle


#8

So, new info. I got a new gas cap and the truck doesn’t have the P0456 code anymore, but at almost half a tank of gas, the problem seems to have come back. It still has a rough idle and I’m thinking it might be more of an issue with the IAC and or dirty/clogged fuel injectors. Thoughts?