The CIS system on the M110 engine uses a separate electronically controlled cold-start valve. It is basically one single fuel injector that sprays into manifold, enriching mixture. Device is controlled by a thermo time switch, which turns on power to the injector. If the injector leaks or runs too long, and overly rich condition exists causing poor idling and greater fuel consumption (poor mileage). Check thermo time switch by unplugging electrical connection at cold-start valve. If rough idle condition persists when power is disconnected, injector is likely leaking or spray pattern is diminished (caused by a dirty nozzle). It is more likely the injector is faulty than a fault of thermo time switch exists.