Toyota '87 22RE Erratic tachometer, misses

[SLC97SR5]

I got the '87 4Runner cranked up today and noticed a miss around 2-2.5k rpm. I drove the 4Runner 20 miles to get it good and warm and then filled the tank with fresh fuel.

When freely revving above 2500 rpm the tach bounces wildly.
It also has a light stumble when the tach bounces.
While driving under load and shifting, the tach bounces, the engine misses and it backfires out the exhaust.

This engine has always seem to run rich to me and there is no cold/high idle.
The TPS is in spec
Timing is good
Plugs and wires are new
Cap and rotor are good
02 sensor is OK
AFM is good
Fuel filter is good
All related connectors have been cleaned and hit with dielectric grease.

The only time the tach fluctuates is when the engine misses and vice versa.

I seem to remember the tach signal to come from the pickup coil in the distributor.

I figure I could shotgun the whole mess with a coil, igniter, pickup/signal generator...I'm looking for some troubleshooting hints.

I'm leaning towards the pickup in the distributor but I cannot remember the interface between the igniter and the tach.

 

[iamsparticus]

I would guess the pickup too but the coil can be the cause also

 

[SUPERFLY]

Make sure all the wires are tight to the plugs, my wires come loose all the time giving me misfires. Also make sure the wires are not touching any metal, it's pretty common for the wires to get burned on the exhaust manifold if they aren't secure. One more less likely cause could be a air leak in your intake, check the rubber parts in the intake tube between your throttle body and the maf. Look closely at it, I've had cracks that are hard to see until stretched out. This causes the motor to run fine while idle or not under stress but when the motor mounts move it pulls on the cracks causing them to expand, creating major vacuum leaks and thus making the motor run horrible under load

 

[SLC97SR5]

I rang out all the wiring per the FSM and everything read to spec.

I checked the air gap of the signal generator/coil pickup...within spec.

I then pulled apart every connection in the system, including the ECU and checked/cleaned all grounds, the problem still persisted. Although it sure starts fast!

Swapped in a spare igniter, problem solved. I guess they start to degrade after 244k

 

[4Chin]

I heard someone say once; parts can still be bad even though the FSM "ohm" checks say good."But there again, just 'cause some 'chits not working, doesn't mean its broke." Nice shotgun fix!