A C182 pilot discovered his mixture control cable had severed; preventing him from adjusting the mixture for his descent and landing from his 9;800 FT MSL cruise altitude. With the assistance of ATC he managed a slow; low power arrival and safe landing at a diversion airport.

Narrative

During cruise at 9;500 FT MSL; I noticed that the aircraft was running high cylinder temperatures; including oil temperatures. I first enriched the mixture; but observed no changes on the EGT or other temperatures on the engine. I proceeded to troubleshoot. I noticed that moving the mixture control in and out didn't change any aspects of the mixture on the engine. I furthered pulled the mixture control to the point I could see the cable from the panel!At this point; I alerted Approach of a possible problem and that I would continue to the destination and maintain my current altitude; fearing that whatever mixture setting I had would cause the engine to shut down at a lower altitude if I did a fast descent.I then noticed that conditions outside were getting worse; so to maintain VFR I asked for a lower altitude and a very slow descent so I would have time to recover the engine in case of a potential stalled engine. This took over an hour and by the time I got to 7;000 FT the engine started running rough. I managed to put the throttle settings at below 13 inches; maintaining a very small amount of power to continue the descent. The Controller switched my status from precautionary to an emergency when I told him my engine was running rough.The Controller then vectored me toward ZZZ airport. I advised the Controller that the ceiling at this point was around 1;800 FT. I had managed to go through a hole on the descent; but now the ceilings were around 1;800-2;000 FT and the reduced visibility from smoke and clouds caused me not to have the airport insight when four miles out. I then asked the Controller what instrument approaches were available and he told me there was an ILS approach to Runway XX. I got out my approach chart and asked for vectors to final on the ILS.I had no more than 9-10 inches of manifold pressure at this point; but I was able to locate the airport about one mile out. I told the Controller I had visual and proceeded to land on the 7;000 FT runway with no incident or damage to the aircraft. I landed with a tail wind as I feared I would not have power to circle to land on the correct runway.I told the Controller immediately that I was safe. I then called the FSS; closed my flightplan; and finally thanked Approach and asked him if I had to report anything to him or the FAA. He said all they were worried about was if I was safe or had any damage to the aircraft and I said no. The next day a Mechanic said that the mixture control cable had come apart leaving me whatever mixture setting I had.