Narrative:

Regarding my IFR flight: I departed from the ZZZ1 flying assigned airways going eastward at an altitude of 9000 ft toward ZZZ2; then north up toward ZZZ3; continuing over ZZZ3 direct to ZZZ. I began my approach to ZZZ; but while descending on the approach my engine began to sputter and run rough. I immediately leveled off my flight; switched tanks and turned on the electric fuel pump. At that point I broke out of the clouds and; because of those adjustments; saw that I was too high to land in relation to the length of the runway. I had a good visual; so began to circle to the left in order to re-position myself to land on runway 28. While on the downwind leg I went back into the clouds. As I turned to the 28 heading; climbing to prepare for another landing approach; my engine once again started sputtering and running rough. I called ZZZ TRACON and they gave me a heading and altitude while I changed fuel tanks again and worked with the electric fuel pump. I was having trouble holding altitude and heading while doing these adjustments with the engine sputtering on and off. Finally; while level; the engine began to run smoothly again and I asked control to find me a nearby airport with the highest ceiling (in case I lost engine I would have good visuals). They offered ZZZ4; gave me the course and turned me over to ZZZ1 approach. ZZZ1 approach vectored me to final. I started my approach; but was too high. They turned me to re-set and I started the approach again; and again my engine began to sputter and quit. I again switched fuel tanks and turned the electric fuel pump back on. During this maneuver I lost altitude and got off course. Control barked this fact to me; but by then I was under the cloud cover and could see the airport. I was lined up for the runway and made the landing with no further incidents. Ground asked me to call him; which I did and in spite of my explanation about engine/fuel problems; he read me the riot act and told me to call ZZZ TRACON; which I did. ZZZ TRACON took my name; address; phone number and my pilot certificate number. After making those calls; I immediately arranged with the FBO to have a mechanic look at the plane and correct the problem. Both main tanks were then filled with fuel and it took 47 gallons; which means that when I landed I still had 29 gallons of fuel on board. This was not a case of getting low on fuel; but a real mechanical problem. Once the plane was being cared for; I notified my family; rented a car and drove to ZZZ. The next day the plane was operational so I drove back to ZZZ4; where the weather was VFR; filed an IFR flight plan and flew over to ZZZ. I did many different maneuvers; but the plane ran perfectly. The next day I again filed an IFR flight plan and flew from ZZZ5 to ZZZ6. The plane ran perfectly. I noticed while enroute that the left fuel gauge began to fluctuate and eventually moved into the yellow area on the gauge. When the left gauge began to move I was already on the right tank. I was concerned that fuel was still pumping from the left tank; even though the fuel switch was on the right tank. On further investigation I could see that the right tank needle had moved off of full; so had confirmation that; in fact; the fuel was being used from the right. As time went by during flight the left tank gauge had returned to the > mark; where it stayed and where it should have always been. Also during my flight south just above ZZZ7 I contacted flight watch for a weather briefing and they informed me that there were cells along my route. Upon re-contact with the controller; I asked for clearance to the nearest airport (which was ZZZ7) to land. He informed me that if I was willing to deviate from my route; he could keep me clear of the weather; which he did. Later; when I thanked him and told him I was grateful for the help; he said; that's what you pay me for. Although as a private pilot what I pay in taxes to support his service probably wouldn't buy him a cup of coffee. Eventually I was turned over to ZZZ3 approach and I requested the GPS approach into ZZZ1. ZZZ3 TRACON informed me that that route of flight would bring me directly through a heavy rain shower and suggested I fly direct to ZZZ1; which was VFR. I followed his advice and then cancelled my flight plan once I landed and was off the active runway. I apologize for any inconvenience and extra work I may have caused to ZZZ TRACON or ZZZ1 approach because of this plane malfunction. My attention was completely engaged. My priority was to keep the engine running and to use all of my skill to keep the plane in the air. I can understand their frustration; but in those minutes; talking was lower on the list of urgent things I needed to do.

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Original NASA ASRS Text

Title: A V35B experienced a rough running engine that caused the pilot to deviate from heading and altitude assignments.

Narrative: Regarding my IFR flight: I departed from the ZZZ1 flying assigned airways going eastward at an altitude of 9000 FT toward ZZZ2; then north up toward ZZZ3; continuing over ZZZ3 direct to ZZZ. I began my approach to ZZZ; but while descending on the approach my engine began to sputter and run rough. I immediately leveled off my flight; switched tanks and turned on the electric fuel pump. At that point I broke out of the clouds and; because of those adjustments; saw that I was too high to land in relation to the length of the runway. I had a good visual; so began to circle to the left in order to re-position myself to land on Runway 28. While on the downwind leg I went back into the clouds. As I turned to the 28 heading; climbing to prepare for another landing approach; my engine once again started sputtering and running rough. I called ZZZ TRACON and they gave me a heading and altitude while I changed fuel tanks again and worked with the electric fuel pump. I was having trouble holding altitude and heading while doing these adjustments with the engine sputtering on and off. Finally; while level; the engine began to run smoothly again and I asked Control to find me a nearby airport with the highest ceiling (in case I lost engine I would have good visuals). They offered ZZZ4; gave me the course and turned me over to ZZZ1 approach. ZZZ1 Approach vectored me to final. I started my approach; but was too high. They turned me to re-set and I started the approach again; and again my engine began to sputter and quit. I again switched fuel tanks and turned the electric fuel pump back on. During this maneuver I lost altitude and got off course. Control barked this fact to me; but by then I was under the cloud cover and could see the airport. I was lined up for the runway and made the landing with no further incidents. Ground asked me to call him; which I did and in spite of my explanation about engine/fuel problems; he read me the riot act and told me to call ZZZ TRACON; which I did. ZZZ TRACON took my name; address; phone number and my pilot certificate number. After making those calls; I immediately arranged with the FBO to have a mechanic look at the plane and correct the problem. Both main tanks were then filled with fuel and it took 47 gallons; which means that when I landed I still had 29 gallons of fuel on board. This was not a case of getting low on fuel; but a real mechanical problem. Once the plane was being cared for; I notified my family; rented a car and drove to ZZZ. The next day the plane was operational so I drove back to ZZZ4; where the weather was VFR; filed an IFR flight plan and flew over to ZZZ. I did many different maneuvers; but the plane ran perfectly. The next day I again filed an IFR flight plan and flew from ZZZ5 to ZZZ6. The plane ran perfectly. I noticed while enroute that the left fuel gauge began to fluctuate and eventually moved into the yellow area on the gauge. When the left gauge began to move I was already on the right tank. I was concerned that fuel was still pumping from the left tank; even though the fuel switch was on the right tank. On further investigation I could see that the right tank needle had moved off of full; so had confirmation that; in fact; the fuel was being used from the right. As time went by during flight the left tank gauge had returned to the > mark; where it stayed and where it should have always been. Also during my flight south just above ZZZ7 I contacted Flight Watch for a weather briefing and they informed me that there were cells along my route. Upon re-contact with the Controller; I asked for clearance to the nearest airport (which was ZZZ7) to land. He informed me that if I was willing to deviate from my route; he could keep me clear of the weather; which he did. Later; when I thanked him and told him I was grateful for the help; he said; that's what you pay me for. Although as a private pilot what I pay in taxes to support his service probably wouldn't buy him a cup of coffee. Eventually I was turned over to ZZZ3 approach and I requested the GPS approach into ZZZ1. ZZZ3 TRACON informed me that that route of flight would bring me directly through a heavy rain shower and suggested I fly direct to ZZZ1; which was VFR. I followed his advice and then cancelled my flight plan once I landed and was off the active runway. I apologize for any inconvenience and extra work I may have caused to ZZZ TRACON or ZZZ1 Approach because of this plane malfunction. My attention was completely engaged. My priority was to keep the engine running and to use all of my skill to keep the plane in the air. I can understand their frustration; but in those minutes; talking was lower on the list of urgent things I needed to do.

Data retrieved from NASA's ASRS site as of April 2012 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.