When i start my 245 up in the morning, after it has been sitting all night, it will start and run fine. But then i might stop the car for a little bit while i go into the store, or whatever, for 10 or 15 minutes. The i start it up again and if this is the second time since i started it up after it had been sitting all night it will give me little accelorator responce. I could slam my foot on the gas and it wouldnt react like it should, like i have no power. so then i let it idle for a few minutes and the car will idle somewhat rough, then it will correct itself and idle fine with much better gas pedal responce. this problem is progressive the more and more i turn it on and off. I took it to a mechanic and he suggested the air mass meter. I foung a used on that worked, and the car seemed like it had a little more power but it still had the problem at start up. Could it be my leaky head gasket, fuel pump, o2 sensor?

The later models have a minor issue with warm starts, but your year shouldn't, and the problem you describe is more severe than normal.

I suspect that an injector is leaking down the fuel line pressure into the intake manifold and flooding a cylinder.

Run a can of Techron or other injector cleaner through it. If that doesn't help, pull the injectors and get them cleaned/rebulit. They are probably due for new O-rings anyway. I have seen mentions on this board of shops that do good injector work mail order, if you can do without the car for a while.

This is a tough one I think. I think it unlikely to be the head gasket, or fuel pump, O2 sensor maybe. But if the O2 sensor I would think it would occur whether you stopped or not.
I'd guess the engine is flooding when you stop the second time. Perhaps a leaky injector dumps fuel in during the stop, and it is too rich upon restart.
Only other mechanism may be a faulty engine temperature sensor, which is open or reads too high and is making the ECU run too rich.
How is your gas mileage?
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744 & 745 16v 4+OD, 245 SE auto, 242Ti 4+OD, 245DL auto parts car