So... no odb2 codes showing.. I've always had a slightly rough start but idle smooths out quickly... I replaced fuel filter and pump about 6 months ago and all 4 O2 sensors within the past month...
when testing fuel pressure I get 35 psi when turning key on but engine off. Immediately when I start the engine it drops to 29 psi and stays there.
Two questions... 1. should the "running" psi be 34-37 as well ? 2. If so what would cause this drop ? fuel pressure regulator or leaky fuel injector or both ?

Oh... 96 D1, 4.0L

thanks in advance.

 

The pressure drops at idle because the fuel pressure regulator is working, allowing excess fuel to return to the tank. If the pressure didn't drop while idling the engine would run rich and probably quit. The rough start seems like a Rover thing, allow the pump to run until it quits before turning the motor over, probably the plenum could use TLC with a good cleaning, trumpets, plenum, throttle bore and plate, IACV and circuits and the PVC noodle. I would check the throttle for wear and air ingress on either side of the plate. Valve gear being worn or out of adjustment can cause rough starts too. The tune on these make them run richer than what you'd think throughout the band, you could make diamonds out the carbon they create.