(1973) 450sl idle /warm-up/wires/parts????????

[zeggate]

My car idles a tad rough. I start car and the rpms are at 1000, it runs for about 15 minutes then drops to 700 rpms. I've had the injectors changed, checked for vacuum leaks. The indie mechanic
says I need better spark plug wires (BERU). Is there something that's being overlooked? Is the warm up time normal. I've read on other posts about the manifold pressure line sensor but can't
locate it. How can I test the plug wires? thanks in advance.