My 1987 4runner is stumbling/hesitating during all phases of idle or driving. I just purchased this truck and it was running poorly when I got it and needed some work. Here is what I have done so far:

new plugs
new wires
new rotor
new distributor cap
replaced throttle position sensor (with a used part)
adjusted the valves
new headers, cat and muffler (entirely new exhaust)
new oxygen sensor
new fuel filter
new accel coil

I adjusted the throttle position sensor entirely to specifications and all the resistance measurements are correct. There are no dead spots in the resistive strip.

I have run two bottles of fuel injector cleaner through the gas tank.

The timing has been adjusted to 5 degrees with the jumper in place (reads 12 degrees without the jumper)

I tested the resistance values of the Air Flow Meter and pickup coil and both were within specified values. The air gap between the rotor tooth and pickup coil is actually slightly under the specified values. (I would have thought it would be over the values)

When I replaced the coil I also gapped the spark plugs at 40 instead of the stock 31. All plugs showed the correct light brown residue. The new coil and plug gap did not fix the misfire problem.

I cleaned the throttle body and once again readusted the Throttle position sensor to meet specified values.

There are no error codes in the ECU.

And still it misses. I can feel it miss at idle and it just doesnt have smooth acceleration.

I was checking the timing again today and noticed that the timing light appears to show the misses by occasionally not lighting up......to me this indicates a lack of spark. I really wish I had an oscilloscope to be certain. If it is the lack of spark causing a misfire then what are the potential problems? I am starting to think the problem is the igniter or pickup coil but I dont want to spend the money on the parts without knowing they are actually bad. (a new igniter is about $400) Can the igniter be tested? Is there any other way to diagnose this problem?

Any help would be appreciated.

Thanks,
Gregg
email - gmcgough@yahoo.com
tel - 512-351-3920

check the connectors on the fuel injectors.
they get brittle and can break or corrode.

I already checked the connectors and they all appear good. This does remind me of one other thing. My temperature sending unit was not working correctly. Basically the temp gauge shows it to be about 1/2 way even if the vehicle has had hours to cool down. I put in a new temp sensor but the symptoms didnt change. It shows cold when I start it in the morning but goes to about 1/2 gauge within a few minutes and stays there until the next morning.

The misfires exist regardless if the engine is warmed or cold.

Which sender did you change? The gauge sender is down between the intake runners as I recall.

The Factory Service Manual would have some ignitor troubleshooting steps. Could also pick up a used one at the junkyard for a test. And search the forum for "injector wire splice" and see if that applies.

I was just outside testing a few things and decided to use my timing light as an oscilloscope of sorts. I connected the timing light (one at a time) to all four cylinders and saw the occasional miss of the timing light strobe.......which seems to correspond to my misfires. This tells me the problem is spark related. Since I have a new coil, new distributor cap, rotor and wires that pretty much leaves the distributor, pickup coil and igniter as potential problems. Unfortunately my manual doesnt give any information on troubleshooting the igniter but my pickup coil passed the resistance tests (although I dont think these tests are definitive). The distributor drive gear onto the camshaft is in good shape as I had the opportunity to inspect it while adjusting the valves. The air gap to my signal generator is below specs and according to the manual this can only be resolved by replacing the distributor. I dont understand why this gap is under the specifications. It doesnt look like there could be any wear on these parts......how would the air gap get out of spec? I have no idea if the ECU is faulty but my guess is that is not the issue. To the best of my knowledge the ignitor is basically the computer that controls the spark....not the ECU. So that leaves the distributor, pickup coil and ignitor as possible problems???

Any help on further diagnosis would be greatly appreciated.

Is the FSM for a 1987 4Runner available online anywhere?

Thanks,
Gregg

Ignitor is basically the driver circuit between the ECU (that controls the ignition timing) and the coil. The '85 FSM (link at the top of the forum) would have testing information (in the IG section), should be similar to, if not identical to the '87.

I cant seem to find this link to the 1985 FSM. Where is it?

It's in the sticky at the top of this section. Follow the instructions for viewing, however.

Also, to better explain, the fuel injector harness has the connectors butt spliced on about a foot or so up the harness; this is the typical culprit in these older trucks, esp if any recent top end work has been done, and the harness has been disturbed.

I found the FSM and it didnt give much of a test. It states to check for 12V at the igniter.

I am not concerned about the fuel injectors right now. My problem is a lack of spark. But that is good information to know. I will probably take the intake chamber off for a good cleaning soon and that should show me more of the wiring that is hiding under the intake chamber.

But what about the igniter? Any other suggestions on testing the igniter?

Thanks,
Gregg

1. Grab a spare coil/igniter/distributor at a junkyard for testing... If this doesn't solve it, you now have a spare set for when it does fail later on.

2. Your temp gauge is "normal"... As in all of ours do it. It seems to mostly affect 1987's and some 1988's. There has been a lot of speculation about possible bad grounds within the dash wiring, but nothing concrete. I have tried every supposed fix to date, and nothing has fixed it for me. I have gotten to the point where I think there was just a bad batch of temp gauges sent out in 1987, not the sender, not the wiring, just the gauge itself. Put in an aftermarket one.