I have the same problem with my EF as you do - and I mentioned it last time you did

My amizing advice is take it to a mechanic, pay lots of $$$$, get him to fix it - then tell me what he did

I've had no luck finding the problem either - but one clue is that it doesn't do it on LPG! So you can rule out stuff like timing, coil etc.

Like yours, its very much temperature related, but you could also look at it as being time related - if the engine is let sit for ages, it gets cold, and perhaps the fuel pressure regulator slowly releases the stored fuel pressure? Not likely unless your fuel pump struggles as well, because that wuold prime up again almost instantly after starting, and you don't have a problem idling do you?

I am still leaning towards the intake air temp sensor, as I replaced the coolant temp sensor just recently to try and fix this - its still the same.

TPS - not likely as you would more than likely see the problem all the time.

MAP sensor - possible, but i don't think likely. (Do a "goose" test in diagnostic mode and see what pops up)

Maybe snap0964 can advise on my next suggestion: The ECU has routines for all running temps. Cold start, warm up, warmed up, WOT etc. I was thinking of doing the following as a test procedure only. Maybe you could unplug the Coolant temp sensor, replace it with a resistor of a value that tells the ECU that its going to be a cold start, then drive the car for a bit.

If you see that the problem seems to remain for as long as you have the resistor plugged in, it might indicate that the problem is to do with the fuel metering in the "cold start" routine.

If, on the other hand, the problem is there, and disappears after the normal warm up time, you might be looking towards another component that is faulty when cold, and seems to come good once it reaches operating temp.

What I might do when I have some free time next, is do this in the opposite manner - I'll work out what the coolant temp sensor resistance should be at normal operating temp, and i'll put in a temporary resistor and start the engine from cold. My guess is the engine won't hesitate at all, if its a learned cold start routine that is faulty. When I say faulty, I don't mean the ECU, just the data that the ECU may have been learning and accepting as gospel every time its cold. I don't even know if the ECU learns when its cold - thats something someone else on here may be able to help out with.

I'll try this with the Temp sensor, then the Intake air temp sensor, and go from there. I'm as stumped as you are, but it can't bee too serious, as my LPG runs 100%

what makes you think its the head gasket? Loosing coolant or compression?

Milky oil?

Oily Milk?