Bit of a rattle

[yankeesiter]

A couple of times recently when I haven't started the Zed for awhile (7 - 10 days), the engine appears not to be running on a couple of cylinders and this is accompanied by a rattle when I start it. Left at idle speed, it clears out after perhaps a minute or two and the rattle disappears. I would guess the rattle is hydraulic valve lifters. The oil pressure is good at about 60psi.

 

When it gets over this little hiccup, everything is fine. Engine quiet as a church mouse with smooth acceleration.

 

The car has had a full service history at Nissans so I'm presuming that the plugs have been changed sometime before I bought it. Current mileage is 77k.

 

Finally on both occasions it occurred after I washed the car and put it away in the garage. I'm sure there is no connection - just paranoia.

 

Any ideas??