The CCV (crankcase ventilation system) is awry somehow. I had a hard-starting issue on my Jeep that was temporarily resolved (for about 5k miles) by disconnecting the tube that connects the valve cover to the intake manifold. I plugged the manifold vac end. Smoother idle and easier starts resulted, but I had the smell you describe under conditions you described. Venting into the intake tube resolved the smell, and my idle is still smooth, but now it's hard starting again. I think blowby coats intake manifolds and makes for hard starting...

Anyway, check the lines from your valve covers. Make sure they go where they should and aren't cracked or disconnected.