1987 22R 2WD A/T 352K miles bone stock,
I've had this truck since 70K miles, has always run & idled perfectly (as have all the 'yotas I've owned). Recently, suddenly, started to idle rough. I have done the following to rectify, so far without any luck:
Replaced carburetor (first with a new cheap chinese knock-off (piece of crap)...then rebuilt the OE carb, then finally a new Weber 32/36 DGEV...new OE mechanical fuel pump, new fuel filter...
deleted EGR system; major tune-up (plugs,cap,rotor,wires,coil,ignitor, checked the distributor pickup airgap), checked timing (0 degrees)...
Adjusted the valves, compression test shows 160 psi all cylinders. Intake manifold vacuum at 20 inches at idle, 40 at high revs...
Tried an alternate fuel supply; bypassed brake vacuum booster, smog circuits...
None of this has resolved the rough idle. It shakes annoyingly at 700 rpm, pretty hard when idling in gear (automatic). And what I really don't understand is that if I pull off #1 or #2 plug wires while idling, it dies quickly, but I can pull #3 or #4 wire off, & it has no effect whatsoever...just idles happily & roughly on 3 cylinders. My timing light insists spark is getting thru all 4 wires, right up to the plugs.
Of course, the new Weber sucks vacuum under the mounting base, but not ridiculously so.
What am I overlooking? Sure, it has 352K on it, but I've had 22R's go to 600K & still could hold a smooth idle...no matter what I do here, makes no difference at all...

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Webers can be really picky about fuel delivery. Not saying it's definitely your problem but in the instalation manual it says you need an electric fuel pump and the max fuel pressure is 3.5 otherwise fuel will make it past the needle when the bowl is full. Another thing to consider out of the box if specifically set up for a 22r it will be set up for sea level. I also found the float level being wrong was the cause of my rough idle before.

 

Missed the part with the dead cylinders. With a Compression test checking out and the brake booster plugged it is weird the back cylinders are only effective.

 

After the third carb install, and they all ran identically, I'm pretty sure it's not a fuel issue. Sure sounds like an electrical miss. But after 2 different sets of plugs, cap, rotor, wires & coil packs, I sure cannot track it down...

 

The ignition module might give you this problem.

 

I swapped the module & coil with a spare I have, no change. I do have new cheap Chinese module coming, and a new NGK stock coil...we'll see if that helps...it's my last hope at this point...

 

You said the timing was at 0°, is that just your base timing or at idle

 

At idle, advance vacuum disconnected. The timing mark stays steady, doesn't bounce around like a sloppy timing chain might...

 

Isn't timing at idle supposed to be ~8° ? The vacuum advance only really takes effect on throttle doesnt it?

 

The sticker under the hood says zero, which is unusual to me...but it's been set at that for 36 years & ran fine...
I tried advancing the timing, didn't affect the rough idle.

 

The only other thing i can think of is a dead/weak cylinder. You mentioned pulling the plug wires and 2 of them would result in the engine dying and the other 2 had no effect. Will it continue to run when you have the wires pulled from Cyl 3 and 4?

 

It will continue to run with just one wire pulled at a time...I have since purchased 4 inline spark plug testers...now I can see what the ignition is doing in real time...had weak spark to at least 1 or 2 cylinders while the others had strong spark, which randomly varied form plug to plug as it sits and idles. So I thought maybe the OE distributor was worn and the shaft wobbly, & causing chaos where the reluctor meets the magnetic p/u. So I bought a new A/1 Cardone distributor (turned out to be cheap Chinese crap, of course...)...that works OK, now have strong spark to 3 cylinders at a time, the 4th not quite so strong...NO CHANGE in rough idle! So I replaced both motor mounts & the A/T tranny mount...NO CHANGE! At this point, I'm out of ideas. I will continue to try to eliminate all vacuum leaks, using gasket sealant on the carb gaskets, and eliminating all vacuum draws (except the distributor advance). Wish me luck!

 

Stupid question, do you have the wires in the correct order?