A big Thank You to everyone who sent ideas on possible sources of the intermittent run-up problems. My A&P/AI finally found a combination of (a) one broken P-lead wire, that didn't quite break all at once, and (b) a fouled spark plug, he said likely due to a slight oil leak from the #4 cylinder.
To recap: symptoms had been (on my first bad run-up) 200 RPM drops on both mags, one of which just kept dropping, and -- even after he cleaned off the sparkplugs at the field -- still an intermittent 200 RPM drop on one mag, even when the mechanic was doing the run-ups. He also started experiencing a failure of the engine to completely quit on shut down, for 3-4 seconds. On some of those occasions, he could even throttle up to 1000 RPM with the key OFF. After he replaced the bad P-lead and replaced 3 lower spark plugs, I test-flew it yesterday for 8 touch-n-goes, and it flew great, engine smoother than before, and all problems gone. If there were any drops on the mag test at all, it was almost imperceptible -- maybe half a needle's-worth. (Is that ok? He said he thoroughly tested the continuity and electrical connections on the P-leads and they are now solid and he's sure they are correct. In the 3+ years I've had it, up until this intermittent problem, my 'Coupe *never* had mag drops more than a couple of needles-width-worth, and now it's even less.) To expedite the testing and repair, he used 3 spark plugs he had on hand that he said were 90%. For a more permanent replacement, Hartmut recommended the REM37BY spark plugs for at least the 4 bottom plugs, but the AI who does my annuals at another field recommended that I get 1 of the iridium fine wire plugs to replace the one that fouled, since they work even through oil. Any problem with those suggestions? Thanks again everyone! It felt **great** to be back in the air! Linda N3437H (Sky Sprite) L.A.
