l don't have the 129 specs, but usually the idle relay sends between 3 and 4.5 volts to the valve. The higher the voltage, the more the relay is trying to slow the engine down. Be aware that a cheap repair for a bad relay or valve is to put a restrictor like a washer or dowel with a hole in it in the air path behind the valve. This cuts the air and slows the idle.

You can test your cold start injector by removing it, reconnecting the gas and electricity, sticking it in a jar, and cranking the starter. Do disconnect the coil so the engine won't start. You should get a small puff at 50 degrees.

The Bosch copper plugs are very hard to find. I have been using the Champion equivalent (N20-somethingY). Everyone seems to have poor luck with the platinums.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe