Bought it in '98 - was my 2nd arm throughout a long stay at college. Left it with parents for 5 years while I lived in Europe. Just moved back stateside, took back the car. It had 220k miles on it when I left, now has 236k on it, so it sat around a lot. A few issues; I'm trying to figure out where to focus efforts. So happy to see such a great forum exists for DIY - I've been reading all over for inspiration, finally deciding to make my first post.
First thing noticed was really rough idle, exhaust sounds like it's regularly missing . This was confirmed by emissions test where it failed HC-idle (1439ppm!). Idle CO = 1.00 (just barely passed in Utah). High speed HC=79, CO=0.03 (both passed). I replaced plugs/FF/PCV/oil/OF, cleaned the K+N AF, and added Bar's Leaks to oil, and a Slick50 fuel system cleaner. Filled the tank with high octane fuel (found out later this was a mistake for lowering emissions). Retested and still got only slightly better results (1296 HC / 1.01 CO idle, 47 / 0.15 high speed).
BTW: Noticed the plug in cylinder 1 was covered in black sooty stuff (both bridge, insulator, thread rim). Other plugs seemed pretty good.
Next step: compression test. Cylinders 2 and 33 at 124 /132. Cyl1 at 48! Added oil and it stayed the same pressure. Cyl4 was at 77, 2nd test was 90. Tired with oil and got 92, 2nd test after oil was 112. As cyl4 is the hardest to get to, I wonder if I didn't get the tester tight enough, thus the low readings. Will try again after running the car a while to do a new "dry" test. Also noticed that the new plug in cyl1 already has an oily residue on it.
Vacuum test: connected to driver's side port on intake manifold. At 4000' elevation, the zero-point on gauge was about 0.3 over-pressure. At idle, got 13.3-14.0 (shaking between those two). At 2500rpm, it was steady at 16.5. When closing throttle, drops to 15 immediately, couple seconds to 14.
My initial thoughts: there's a lot of unburned fuel coming into exhaust. Was worried that the cat was damaged and blocked up, but the vacuum test didn't take long to drop back to idle levels, so maybe the cat's still OK. My guess on cyl1 is worn valve guide as there's oil on the new plug, and dry/wet comp test gave same really low pressure.
Anyone have a better diagnosis? If it is a valve guide - this requires an engine pull, correct? Trying to decide on worthiness of all the work for such a rust bucket. Thanks in advance.