1998 s90 bizarre behavior at high speed and start
 

So here's the situation. When the car is being driven over 60 miles an hour and it seems like it's warmer out or the engine has been running for a while, it starts hesitating at high speed.
But, This is the weird thing. I can tell if it's going to hesitate when I start the car. If it takes more than a couple seconds of cranking before the car turns over, I know when I get to the highway it's going to hesitate at high speeds. If it starts normal, within a second or so of turning the key, I won't have a problem. We've had screwy Spring weather but it seems like this problem shows its head when the outdoor temperature is above 60 degrees but that could be coincidemce.
Oh, and none of this happened when I had a loose engine oil cap that was spattering oil. After replacing the cap, this all started. Coincidence?

Any thoughts?

recently replaced the plastic molded air intake boot by the throttle because it had a huge crack in it, I thought that might solve it oh, but it didn't.
thanks!!

there is one connection between the oil filler cap and the intake - that's the PCV system. The PCV is supposed to run the blow-by gasses from the crank case into the intake. If you have a bad oil separator (aka flame trap), it can create a vaccuum leak or allow oil to be sucked into the intake. Now the tie in to the oil filler cap is if you have a PCV system issue and too much crank case pressure, the old filler cap probably allowed pressure to bleed off vs going through oil separator - and putting on a new cap changed that dynamic. Well, that's my theory :-) next step is to test for positive crank case pressure (ie do a "rubber glove test" or have a shop measure the pressure) to see if its in spec. You can also try pulling up the dipstick as a vent for the crankcase pressur to see if that cures your hesitation as well.

thanks for the theory, will check it out!!