>>It's seems unlikely that that would be the problem.<<

At first I thought "acr" might have meant the common crankshaft sensor problem but from what I have read that doesn't usually give you a CEL. The same source said the camshaft sensor is likely to produce the CEL when it goes bad. In GA, nobody can pass the emissions test if a CEL light is on, so the problem may not be emissions related - just the general fact there is a CEL.