Narrative:

Departed [in the evening for return flight]. The weather was marginal winds [which] had decreased; ceilings were around 2;000-2;800 with precipitation along entire flight. Departed north bound activated VFR flight plan. [Within about 25 nm] we confirmed we were going to have to stay low along [the highway]. To the west there was blue sky; we decide to climb to fly VFR on top back to [where] there was VFR conditions at with sky clear. As we climb to VFR conditions we were on top at 9;000 feet MSL as we continue north we were caused to have to climb higher after 20 miles at 9;000 feet. To continue VFR conditions we were at 12;500 feet. Temp was -12c wind was 200 @ 40 kts. As we approached ZZZ we experienced light engine roughness; at this point the sun was beginning to set; we were above a solid overcast layer at 13;000 feet MSL with freezing levels at 5;000 feet MSL. We were trying to circle and try and find a hole over ZZZ. I tried to improve the engine roughness with adjusting mixture for altitude; carb heat. When I pulled carb heat I had a severe engine drop in RPM at this point I realized we were in a emergency situation and there was a possibility we could have an engine failure with the temperature so cold the carb heat was not effective. The temperature dew point spread was within a degree of each other. After a few minutes of trying to find a hole in the overcast layer and troubleshooting the engine roughness I called ATC center as I was not on flight following at the time. I called them and [advised them of the situation] and they gave me a transporter code. They asked me my intentions I told them I needed to get on the ground soon and I did not have the ability to shoot an approach and the risk of ice. ZZZ1 was reporting VFR conditions ATC advised me to continue to ZZZ1; the precipitation was the lightest. They cleared me to ZZZ1 via radar vectors 270 heading; at this point I was at 13;500 feet they wanted me to descend lower I told them I needed to stay VFR for ice conditions so I requested to stay higher they cleared me for 14;000 feet. As I was heading to ZZZ1 I realized I was facing a 40 knot head wind with a ground speed of 38 knots; temperature -15c. As we were heading towards ZZZ1; is where things started to get worse the engine was running very rough at this point I could not maintain altitude I was just on the edge of stall speed with the stall warning going off. I advised ATC that I would not be able to make it to ZZZ1 and asked them for any other airport nearby with better weather there was nothing with better weather that we would be able to stay VFR. I made the decision to attempt ZZZ knowing I would have to take a C162 IMC into ice conditions. At this point I did not see any other options with the engine running so roughly and not improving. I definitely thought the engine was going to quit with carb heat on and barely running. ATC instructed me to turn to a heading and decided to 7;000 I used G300 to find ZZZ airport put the GPS into obs mode and selected heading 120 for runway 12. I entered IMC at 13;200 feet MSL -14c; the sun had set by now and it was dark the temp was dropping we were picking up ice on the descent. I was descending at a rapid rate to get to warmer temperature. ATC was talking me though different heading to fly to get me lined up for the airport runway 12. They were able to get me to 4;000 feet MSL we were still IMC with temperature +1c. They could not clear me any lower with the runway in front of me. I changed to unicom 122.8 so I could turn the runway lights on. I turned on terrain function on the G300 and descended lower to see the airport at 3;500 feet MSL. I went back to ATC to report field in sight and I was going to land there. We were greeted by the fire department and emts. I called FSS and closed VFR flight plan.

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Original NASA ASRS Text

Title: C162 pilot reported diverting through ice and instrument conditions due to a rough running engine.

Narrative: Departed [in the evening for return flight]. The weather was marginal winds [which] had decreased; ceilings were around 2;000-2;800 with precipitation along entire flight. Departed north bound activated VFR flight plan. [Within about 25 nm] we confirmed we were going to have to stay low along [the highway]. To the west there was blue sky; we decide to climb to fly VFR on top back to [where] there was VFR conditions at with sky clear. As we climb to VFR conditions we were on top at 9;000 feet MSL as we continue north we were caused to have to climb higher after 20 miles at 9;000 feet. To continue VFR conditions we were at 12;500 feet. Temp was -12c wind was 200 @ 40 kts. As we approached ZZZ we experienced light engine roughness; at this point the sun was beginning to set; we were above a solid overcast layer at 13;000 feet MSL with freezing levels at 5;000 feet MSL. We were trying to circle and try and find a hole over ZZZ. I tried to improve the engine roughness with adjusting mixture for altitude; carb heat. When I pulled carb heat I had a severe engine drop in RPM at this point I realized we were in a emergency situation and there was a possibility we could have an engine failure with the temperature so cold the carb heat was not effective. The temperature dew point spread was within a degree of each other. After a few minutes of trying to find a hole in the overcast layer and troubleshooting the engine roughness I called ATC center as I was not on flight following at the time. I called them and [advised them of the situation] and they gave me a transporter code. They asked me my intentions I told them I needed to get on the ground soon and I did not have the ability to shoot an approach and the risk of ice. ZZZ1 was reporting VFR conditions ATC advised me to continue to ZZZ1; The precipitation was the lightest. They cleared me to ZZZ1 via radar vectors 270 heading; at this point I was at 13;500 feet they wanted me to descend lower I told them I needed to stay VFR for ice conditions so I requested to stay higher they cleared me for 14;000 feet. As I was heading to ZZZ1 I realized I was facing a 40 knot head wind with a ground speed of 38 knots; temperature -15c. As we were heading towards ZZZ1; is where things started to get worse the engine was running very rough at this point I could not maintain altitude I was just on the edge of stall speed with the stall warning going off. I advised ATC that I would not be able to make it to ZZZ1 and asked them for any other airport nearby with better weather there was nothing with better weather that we would be able to stay VFR. I made the decision to attempt ZZZ knowing I would have to take a C162 IMC into Ice conditions. At this point I did not see any other options with the engine running so roughly and not improving. I definitely thought the engine was going to quit with carb heat on and barely running. ATC instructed me to turn to a heading and decided to 7;000 I used G300 to find ZZZ airport put the GPS into OBS mode and selected heading 120 for runway 12. I entered IMC at 13;200 feet MSL -14c; the sun had set by now and it was dark the temp was dropping we were picking up ice on the descent. I was descending at a rapid rate to get to warmer temperature. ATC was talking me though different heading to fly to get me lined up for the airport runway 12. They were able to get me to 4;000 feet MSL we were still IMC with temperature +1c. They could not clear me any lower with the runway in front of me. I changed to UNICOM 122.8 so I could turn the runway lights on. I turned on terrain function on the G300 and descended lower to see the airport at 3;500 feet MSL. I went back to ATC to report field in sight and I was going to land there. We were greeted by the fire department and EMTs. I called FSS and closed VFR flight plan.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.