What could it be?

[selavia]

Diagnosis help appreciated: Not a BMW; it's a 1996 Camry V6, auto. 122k miles

The problem: Inconsistent start timing. Sometimes it will crank and start within a split second, other times ignites after 2-3 seconds, sometimes 5-6 seconds, other times as long as 9-11 seconds. Additional, when it take 9-11 seconds the car will hesitate slightly at start up and you can sense the automatic choke, (do cars still have that?) or whatever the equivalent to that is, kick in and rpm idle around 1500rpm for less than a minute before falling to 1000 where it usually idles when cold. It always starts though.

Things already Replaced & maybe helpful bits:
Spark Plugs. (Old plugs were clean, just worn; no oil deposits, no corrosion, nothing) (NOTE: this car has coil packs and no spark plug wires or distributor)
Fuel Filter (I think, I'm not sure)
Fuel Pump has been checked, fully operational
Fuel Injectors cleaned (with Redline S1-1) 2-3 times
Throttle body was removed and cleaned thoroughly
MAF Solenoid was replaced (was triggering a Code)

The car has a cold air intake. The filter sits behind the driver's side air dam which is for the brakes. The car has been lowered as well. (I was wondering if the CAI is the cause for the uneven starts; I am not sure if this conclusion makes any sense) I suggested to the owner to put the original air intake system in, but he says he is 100% sure that is not the problem.)

I'm thinking there is a problem with the air coming in the engine on start up; so I'm also thinking MAF meter or sensor (temp sensor).

Any thoughts, suggestions? Really just looking for input and suggestions. I had posted one of these before a different Toyota and I found Kirby's advice resolved the problem, so I'm hoping for some more nuggets of wisdom.


Thanks, Sean

 

[Kirby]

The fuel pump probably has a back flow check valve in it, so that the gas does not drain from the fuel line when it is not running. The fuel pump can be fully operational, but the check valve can leak back, starving the fuel supply on start up.

Is there a pattern - overnight it takes longer to start, while if it's a quick restart after 15 minutes, it fires up faster? If so, that's very typical of a leaky check valve.

 

[selavia]

Kirby, that's very stereo-typical of the problem; after sitting for +4hrs, it does it, but if started right after that, starts normally.

Where would one likely find the check valve and how would you test it before replacing (if you can)? I guess what I'm asking is do you have to replace the fuel pump, or is a part of the fuel pump?

 

[selavia]

Kirby, do you think the sending unit should be replaced as well or just the pump?