91 500 SL fuel pressure regulator
 

My engine has a miss at idle but smooths out over 1500 rpm. Someone told me the fuel pressure regulator might be leaking internally. Where is it located and how can I test it? Thanks in advance for you assistance.

I haven't done much with the V8 so can only offer generalities.

Electronic fuel injection has a vacuum referenced fuel pressure regulator at the end of fuel rail. ( fuel and a wire running to each injector )

I _think_ you car has CIS, in that case the fuel distributor is what controls fuel. ( thin steel tube running to each injector , no wire )

This car probably has 2 distributor caps , check the caps for carbon tracking, measure resistance of plug wires, pull plugs look for a bad one.

I have the exact same issue in my '95 SL. I'm swapping out the plugs this weekend (unsure of when that was done last.. for all I know they're original like everything else I've found) and will report back.

I have changed the distributor caps (2) and both rotors and all 8 plugs. The spark plug wires all have the same resistance and look fairly new. The plugs I pulled out all looked very good and were all clean. All cylinders have good compression +- 5 psi of each other. I am puzzled.