Hard starts with Castrol Syntec 10w-40

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Oct 30, 2003
Bakersfield, California U.S.A.
I just recently switched to Castrol Syntec 10w-40 from the German Castrol I had in before. Vehicle is a fuel injected 383 stroker motor. I have never had starting trouble untill now (motor normally fires up very fast....and sounds mean)

Motor will start fine for first two seconds ..... untill oil pressure rises, then it stumbles over for a couple seconds. Sometimes it will die completely. I'm at a loss
and dont know what to do.

I pu this oil in because it was a thin 40 weight (85.4 @ 40*C and 13.1 @ 100*C on a recent VOA) but had no idea it would act like this

I should mention that my throttle body is modified for idle reasons to accomadate the more radical cam, but not sure if that would affect it that much.
I know nothing about that Yankee motor (
), but I don't see how the stumbling and stalling could possiby be oil-related. I'd rather suspect a problem with the idle control valve (if that engine has one), the MAF, the coolant temperature sensor (not kidding!) sensor, or the throttle position sensor.
The reason I look to the oil is because there was absoutely zero issues before the oil change, and the churning/stumbling is directly related with the oil pressure rising. Could it be lifter related? I normally would never "blame" such an incident on the oil, but I'll look into what else it could be. I keep an eye on this engine very carefully i.e. check plugs, sensors, under engine, connections, etc. on a regular basis. However, I know the claim sounds hokey.
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