Engine Shaking Rough Idle SOLVED... mostly
 

I have been continuously using the pages on this site to help rebuild my great-grandpa's old 1985 Toyota Pickup 4x4 22r and made some good progress over the weekend that I wanted to share for anyone experiencing similar issues.

The problem: Ever since I got the truck a few months ago (98,000 miles) I experienced problems at idle and low rpm. I believed I was experiencing the engine missing at idle due to a fairly constant sputtering at anything below 2000 rpm including idle and while driving. While driving the engine seemed to lurch and stutter when below 2000 rpm. I was able to get the idle set to 750-800 rpm but it still sounded like it was missing. The motor was also shaking quite a bit at idle enough that it would shake the entire truck and could be felt in the cab.

Steps taken: After reading on this site, I first replaced all of the spark plugs with NGK V-Power Nickel BPR5EY, the wires with standard Orielly brand wires, the fuel filter with a clear Orielly filter, and had already replaced the whole distributor previously due to a failed timing adjustment diaphragm. Oil and filter were replaced as was the air filter. I ran a Seafoam through the fuel system as directed on the can and also used the Seafoam spray directly into the carburetor while the engine was running until the white smoke stopped pouring out. I double checked the timing with a timing light, (12 deg with vacuum attached, 0 deg as stated on my hood with vacuum line removed). Everything seemed to run smoother after this, but it still sounded like the engine was missing and stumbled under 2000 rpm while driving.

I attempted to unplug one spark plug wire at a time while the engine was running to see if one plug wire being removed could be identified as misfiring cylinder but could not tell for sure. Between trying not to burn my hand on the exhaust manifold, avoiding the spinning belt next to the distributor and occasionally getting shocked by the wires as they arc 'ed I can say I did not get very good data. Next, I began checking for vacuum leaks with starter fluid. I didn't find anything significant but did replace most of the vacuum lines connected to the carb just in case. I also found a blown Auxiliary Acceleration Pump (AAP) diaphragm and replaced it with one from a kit from Orielly. This drastically improved gas mileage but did not solve the idle and misfire problem.

I had not done a full carb rebuild yet but noticed my fuel level in the sight glass seemed to be too high. It was not all the way at the top of the glass, but it was much higher than halfway. After adjusting the float per the factory spec, the fuel level was still too high. Next, I replaced the needle valve with one from the kit but noticed no change. Finally, I had to adjust the float height outside of the factory spec but was able to get my fuel height perfectly centered in the sight glass.

After pulling the spark plugs,
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I noticed cylinder 3 looked very wet and black. This led me to back to the advice of nearly every post I have read which says check the valve adjustment.

The potential fix: I had been avoiding adjusting the valves due to an oil leak on the back of the valve cover and the fact that I had never adjusted valves before. I was able to get an aftermarket gasket kit with the main gasket, top bolt rubber pieces and half-moons. After warming up the engine, setting the timing mark on the crank pulley to 0 degrees and making sure the distributor was pointing at cylinder 1, I checked the valve clearances the first four valves per the service manual, then rotated the crank 360 degrees and did the other four. (.008 intake and .012 exhaust) Most of the valve clearances were a little tight and I adjusted accordingly but both intake and exhaust on cylinder 3 had no clearance.

After getting all of the valves adjusted correctly and half-moons installed with black RTV, the misfire seems to have mostly disappeared. The engine no longer has a sever shake at idle and runs way better below 2000 rpm when driving. I can actually take neighborhood corners now in third gear rather than having to always down shift to second and give it some gas. After running for a few hundred miles the cylinder 3 spark plug no longer looks wet and dirty and matches the other plugs. There's a strange tapping from the fuel pump now but I believe that is a separate issue I'll bring up in another post.

I've never messed with valves before, but I believe I understand the basic concept. It makes me think that with no clearance on the cylinder 3 arms on the cam that the valves could have been prevented from closing all the way resulting in lack of compression and misfires. Does this sound right? I was also surprised that after 100k miles the valve clearances had gotten tighter than factory. I do not believe the valves have ever been adjusted and I did not see any wear on the camshaft. I would have expected that as the engine got older the clearances would have gotten looser. My only theory is that if for some reason the valves or their seats have worn or the valves themselves have stretched, it would cause the clearances at the camshaft to get tighter.

Questions:
Does anyone know if valve clearances getting tighter over time suggest potential issues with the valves or their seats.
Is this something I should be inspecting or worried about?
Is my theory on lack of clearance between the rocker arm and camshaft causing misfiring, correct?

Overall, the truck drives way better than ever before and the shaking has almost disappeared. I don't have enough data yet to comment on the mpg. I expect it to be slightly better, but I was already getting 18.5-20.5mpg per tank which I believe is pretty good for a 4x4 with stock tires and 4.10 gearing.

Many thanks to everyone on this board for the help that has gotten me this far and as always, any insights, comments or criticisms anyone has on what I've done are much appreciated.

I have a Honda CRV with B20 engine that are known to suffer valve seat recession. They definitely have gotten tighter over time to the point where they start to run rough and will burn an exhaust valve if the adjustment is not made. I have not heard of it on a 20/22r but i believe it could be possible. Or, the last person who adjusted them messed up. Did it previously have a headgasket replacement?

The previous owners were my grandpa and great grandpa. They used it as a farm truck with a big diesel transfer tank in the back to refill and grease farm equipment. They have both since passed but everything I have heard from family is that they never had to mess with anything on the truck, "it just always ran". I found all the documents and receipts in the glove box and the only one from a shop was for muffler work. So I don't believe the valves had ever been adjusted nor the head gasket touched. Everything I've seen so far has been 100% from the factory.

Luckily between the leaking valve cover, leaking front crank seal, diesel everywhere and buckets of overflowing grease in the bed the whole truck had a nice protective coating of diesel, grease, and kansas wheat dust that seems to have prevented nearly all rust and corrosion!