This '91 190E is new to me, and I am attempting to work out its problems.

In trying to diagnose a cold idle roughness, I decided to inspect the Bosch plugs, partly based on reports here. Cylinder #2 was right at .040", and #1 and #3 were only a hair more - which I adjusted to .040". Plug #4 was a different model from the first three, and gap was larger than any of my gauges - at least .060", and apparently designed to be that way. Temporarily, I readjusted to about .040" (kind of angled funny outer electrode now) and the problems have pretty much cleared up, as well as overall driveability and off-idle throttle response.

My question is regarding what the correct model plug would be. This is a CA model, if that makes a difference. Plugs 1 to 3 are currently H8 DCO, and plug 4 is HR9 DCY, which I am certain is wrong. The Bosch site lists H8 DC - how is that model different?

Thanks. Steve.