Cold start stumble question

I already looked up prior posts on this issue. I know that there was a lot of speculation regarding possible low battery, injector leak down, dirty MAF sensor etc. However, I haven't come across any definitive fix for it.
I have had my car for over a year now. During the first year, I had it stumble only two or three times. Once was definitely caused by me not waiting for the "OK" light, the other two seemed to be random. Now all of a sudden, for the past month, it has been stumbling on a cold start EVERY time!! I'm not happy about this.
My question is:
Why would it start doing this all of a sudden for no apparent reason? I use the car regularly, and take it for long spirited drives every time I use it.
I already tried resetting the battery and doing the proper drive cycle. I then tested the battery with a load tester and it showed 12.65 volts after a normal drive and 720 CCA. I also had put in a bottle of Techron a few months ago, along with new spark plugs (the Techron and plugs were done prior to having the cold start stumble. Ran fine for months after that as well).
I can't figure out why this is happening and it's driving me nuts. For now I'm just shutting down and re-starting for the first start of the day. It always starts perfectly the second time. I would also like to add, another Ferrari buddy of mine (in Texas) said that he is having the same EXACT issue! He said it was fine for the first year of ownership, now all of a sudden it stumbles on EVERY cold start, just like mine!
What am I missing? Any ideas?

 

Nope, the oil does not have any fuel smell to it.
I have a fuel pressure gauge that I can hook up for a reading. I'll try to find info in the WSM, but do you know off hand, am I supposed to check it while running? Not running? Sitting over night? I've been thinking about the fuel pressure as well, but didn't know what or when to check it. Time to read the WSM

 

Thanks!
I just looked in the WSM. Basically they say to start the car and check that the pressure is 3.45 bar when running. Then shut off for an hour and make sure that it stays at 2.7 bar.
If it doesn't hold, they say to check for leaks (very generic) and/or replace fuel pump, and/or replace boost control (I assume that's the pressure regulator built into the pump so I would need a new pump either way probably).
When it mentions "check for leaks" would that also mean checking for a leaky injector? If so, how do I narrow it down? Or do I just remove all the injectors at that point and send them out for cleaning/testing at a professional shop?
It seems pretty easy to remove them on this car.
I wonder if it's just a weak fuel pump? I guess I'll know soon enough after I test it. I'll try to do this test tomorrow and report back with my results.
By the way, the car works perfectly in every other way. The drivability is perfect, it's just the cold start issue that alerted me that there is a problem.

 

Thanks Curt, I'll keep updating. Hopefully I can get to the bottom of this!

Please let us know. As I mentioned I put in Techron already (I did it a few tankfuls prior to this issue happening)

Sorry, I forgot to add that the battery was fully charged at the time. I used to put it on the charger if I wasn't going to use the car more than once a week. Since this problem started occurring, I left it on the charger every night. Unfortunately that didn't help..... I was sure hoping that it was a battery issue. Do you think it's possible that the car is so sensitive, that even with more than 12.65V and 720CCA, that the power may still dip low enough to cause an issue?

 

I really don't know what they mean, but they seem to coincide with what the shop manual states.
Shop manual states:
- connect gauge
- start & idle engine
- gauge should read 3.45 bar (~50 psi)
- turn off engine
- check that pressure DROPS and remains steady at 2.7 +/-.3 bar (39 +/- 4.35 psi) for AT LEAST AN HOUR.

The part that I put all caps on is the parts that confuse me a little. According to the shop manual, it seems like the pressure is supposed to drop (or else there is a problem), and the pressure remains steady for at least an hour (that tells me that they don't expect it to hold pressure for 24 hrs)
I don't know if that was a language translation issue, or a comprehension issue on my part but I don't really understand what is "normal" based on the shop manual info.

Anyway, here are my personal results of my test:

-I started with hooking up the gauge after the car was sitting for 24 hrs without being started. Both left and right banks showed 0 psi.

-I left the gauge on the left bank and turned the KOEO (key on engine off), then checked the pressure. It was at 48 psi (pump prime)

-I started the engine, waited 10 seconds for the gauge to stabilize at 53 psi

- Shut engine after 1 -2 minutes of running then took reading after 10 seconds, 48 psi

- took reading 1/2 hr later, 45 psi
- 1.5 hrs later, 37 psi

Then I repeated the test with the right bank:

- KOEO, 48 psi

- Start engine, 54 psi

- shut engine after 1-2 minutes of run time, 51 psi

- 1/2 hour later, 51 psi (this was strange that it didn't drop???)

- 1.5 hrs later, 44 psi


Looking at all my data, it seems to fit into what the shop manual expects the readings to be:
They were both over 50 psi with the car running.
They were both 39 +/- 4.35 psi after sitting for at least an hour. (actually the right bank was slightly higher pressure than the spec in the service manual)

Based on all this info, can I assume that the fuel pressure is not a cause of my issue? Or a cause?
I'm thinking that it's fine at this point.

 

Curt,
Are you referring to my fuel system? Does it all appear normal to you? Should I move to another possibility? Assuming the fuel situation is normal, I now reset the computer, checked the fuel and charged/checked the battery. What would you recommend next?
Is it possible that I just got a bad tank of gas? I believe that this whole cold stumble issue is happening on the same tank of gas so far. I went through a little more than 1/2 of it so far, so a fill up is probably a solid week away from now (there is going to be some rain during the week....yes it WILL melt if I use it in the rain, LOL).

 

Should my next step be to clean the MAF sensors?
If so, how do I go about it?
Do I pull the air cleaner covers and spray cleaner in there, or do I find the proper security bit, and remove the MAF sensor out of the side of the air tubing to clean it?

 

Awesome! Thanks

 

Are there any vacuum lines in particular that I should focus on? Are there any lines that are buried under the side panels, by the gas tanks, or are they all by the intake manifold?

I used to have a 1986 Mustang Gt that had issues with the air bypass valve. I guess the valve acted as a choke sort of. If that thing got dirty, the idle would hunt around a bit and have trouble with cold starts. Is there anything similar on this car that you know of? I don't think that's the issue because in this case, 1 bank of cylinders is simply not firing at all, it's not just running rough. I just figured I would throw it out there since I'm at a loss.

 

I checked all of the hoses that were visible, and they seem ok. They are not dry rotted (they actually feel brand new and clean) and they are all connected tightly. The intake hose clamps were also very tight and the bellow tubes didn't budge at all.

I also had a problem that I posted about in the past. It never bothered me too much so I didn't follow up on it, but now I'm wondering if it's related to this problem I'm having now. The problem I've noticed since I bought the car is that when the engine is cold and I give it a little bit of abrupt throttle, the rpm's drop to about 500, then it catches and comes back up. It doesn't do this after the engine is warmed up for a few minutes, only from a cold start. I'm thinking that this issue may be associated to the MAF sensors. Is it possible that both problems that I'm experiencing are related?
Here is a video of the RPM drop:
[ame]http://www.youtube.com/watch?v=egob5AkPy1E[/ame]

 

I already put in Techron a few tankfulls ago. It was even before I had this new issue. I was trying to fix the issue in the above video, it didn't work