... Is there a particular brand of fuel additive you'd recommend? I've used SeaFoam in the past but it's been a while. ...
I’m not familiar with injection system cleaning additives in the US market. It should be a petroleum-based product. I had good experience with “Injection Reiniger” from “Liqui Moly”.
... Between pins 1 & 2 the resistance is .2. The resistance goes to infinite just after the throttle linkage disengages from the wheel on the unit labeled s27/2 in the image attached to post 86. This corresponds to a slight depress of the gas pedal, maybe 1/8th of the full range of motion. s27/2 is the decel fuel shutoff switch or something like that, correct? ...
That’s how it should be. But you should see the same resistance between terminal 13 & 2 at the ECU connector !
… I suggest to check the resistance there again and if you still measure what you reported in post 98 (4.97 Ω with the pedal depressed), measure again with the TPS connector disconnected.
The micro switch S27/2 does several things, but ECU terminal 13 is the input terminal for the closed-signal of the TPS (Throttle Posisiton Switch). S27/2 is supposed to open before the TPS opens, as you observed.
... As for pins 3&2 I had infinite resistance regardless of throttle position. This proved true whether actuating the throttle with the gas pedal or manualing moving the linkage. ...
If you don’t see less than 1 Ω between pins 3 & 2 with the pedal completely depressed or with the throttle completely opened manually, there is a problem with the TPS’s WOT-signal, which is not relevant as for the symptoms you have reported so far and can be taken care of later.
... As for checking the camshaft, is there anything in particular I need to look for? Is removing the oil dripper absolutely necessary or just recomended? Where can I use that 27mm socket to turn the crankshaft and how would removing the sparkplugs make it easier? Is cleanliness a major concern? Most of the places I would be able to perform this are relatively dirty (farm garages or woodshops) and my engine has a lot of grease and grime on the exterior.
If you can see any camshaft lobe that resembles the first one in the attached image with the oil dripper installed, then you have seen enough and don’t need to remove it.
The 27 mm socket is used on the head of the bolt that sits in the front end of the crankshaft (behind the fan). With the spark plugs removed there’s no compression, which reduces the torque required to turn the crankshaft significantly.
If turning the crankshaft manually is too much trouble under the given circumstances, you can also use the starter via ignition key. However, you should deactivate the ignition system to prevent the engine from firing. You can do that by disconnecting the coaxial CPS plug from port 2 of the ignition control unit (see attached image). It’s located on the left fender well.
As for cleanness … if the valve cover is dirty, clean it a little, so that no dirt gets into the valve train area when you remove it and when you put it back. If not too much dust is flying around in these farm garages or woodshops, it’s okay … and if chicken are running around there, keep ’em out of the engine bay while the valve cover is off. …