Lifter problem?
 

I have a 1998 Expedition with 4.6l. When I got it a few months ago It had a broke timing guide on drivers side so I replaced entire timing set. Also had to replace the alternator because it was clicking. The past two weeks I have been hearing a clicking noise. It clicks for about 15 seconds and then stops for about 30 seconds then starts again but only at idle. I believe it is a lifter but do not want to tear into this motor again unless I really have to. My oil gague in my cluster does not work neither does my check engine light due to a bad cluster. I tested that out by replaceing the oil sending unit with a new ford made one. Just want a second opinion if this is mostlikely a lifter or not. Also just fyi i know I have a blowen exhaust manifold gasket on the drivers side when the noise comes from so could it be a valve?