I've got standard equipped a 95 Civic EX (1.6l D16Z6) that has recently started misbehaving. I do most of my own tune-up work--valves, plugs, timing, & oil. 110K miles.

About a year ago, when I was putting the valve cover back on, I noticed that the breather hose that clamps to the valve cover was cracked. I drove it anyways (probably not smartest thing to do), and it was OK, but it did hesitate just a little at low RPMs (<2200) at cold and hot. On Friday, it got noticibly worse overnight. The check engine light never came on.

On Saturday, I check the the valve lash, & replaced plugs (forgot to look at them closely--they were a little black, but I don't think the electrodes were fouled--will check when I get home this evening). I also changed the oil & filter, air filter, adjusted the timing and replaced the cracked breather hose. I also scraped off some old RTV at the corners of the valve cover, but did not put new RTV in it's place.

The car ran great, and I drove it 3 times over the weekend for maybe about 10 min at a shot. I also added gas and fuel injector cleaner. I did some reading and pinched the PCV valve hose--I can't be sure I heard a click the 1st time or two because I wasn't sure what I should be listening for. When I pulled the valve out and covered the bottom, it clicked and the RPMs took a dive, but the car continued to run.

This morning, the car ran fine until the 10 minute mark where it picked up all the old habits again--rough and hesitant until about 2800RPM. I drove it some more at lunch today and again, it's fine until it's been running for ~10 minutes. Again, I'm not seeing a check engine light.

I'm planning on checking for vacuum leaks this evening (did a search and found the carb cleaner trick) and I feel pretty confident that I'll need to put some RTV on the valve cover, and I picked up a PCV valve at lunch.

Is there any reason to think that it might not be a vacuum issue? If I still have the problem tomorrow, what else can I look into without special tools/gages? I guess I should replace the plug wires at this point as well...

TIA,
Ty