I know, this could be any one of a million things, but after finally finishing the valve cover/upper timing chain cover replacement on my 03 4.4i, it has a very rough, unsteady idle which doesn't smooth out as I rev the engine. The job was complicated by the fact that I dropped the timing chain tensioner plunger into the lower timing chain cover, which required me to take a ton of stuff off (alternator, water pump, PS pump, belts, front pulley, etc.). The symptom sounds very much like a vacuum leak, but so far all the hoses I've checked are tight. The other symptom is that the service engine soon light is on, and it systematically cycles between being continuously illuminated, and flashing. Could this imply a loose sensor connector? The SES light wasn't on before I started the project. I haven't taken it to an auto parts store yet to get the codes read, because I hesitate driving the vehicle with it running so rough, but depending on the opinions I get, that could be my next step. Thanks in advance.

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2003 X5 4.4i
1992 Porsche 968
2007 328i
2014 Subaru Forester XT