Ok, here's the short hx, bought a 90 4runner in 9/13 with 173k. It's a 3L AT, very clean, had CARFAX, truck spent most of it's life in Va Beach.
Less that 1000 miles in, blown head gasket. I live in remote NNY, no real Toyota service close by. Nearest Toyota garage wasn't too interested in replacing engine. No machine shops within 120 miles willing to look at it, w/o a ton of $$.
Bit the bullet, shopped and bought a rebuilt 3VZE from Phoenix engine rebuilders. Found a good Mechanic(used to work for my regular garage guy,I knew him from years ago). He is ASA certified, works primarily on Commercial Vehicles for a large local agency. Also has a garage and small business on the side. He takes on the job, fitting in as he has time, and I'm not in any real hurry as I was recovering form a bad fall. Calls me 2 weeks ago, got it running, has a code 52, he is going back in to replace the harness. Replaced harness, replaced Knock sensor, still has code. BUT...engine runs to spec, OD works, mileage is off a little, 2-4 mpg lower on new engine, less than 500 miles...calls me up, says to drive it, mayber it'll clear itself...
this is also posted on 4runner Forum as I'm looking for some insight

BigBoox

 

The good news is that your mechanic did all of the things I would have done (replacing the "pigtail" and the sensor).

Anything could happen (a wire could jiggle back into place, for instance), but I doubt driving your truck will ever fix a code 52. The "symptom" of a code 52 is severely retarded timing, resulting in very sluggish response and poor mileage. Your mechanic could have set the base timing so advanced that the ECU's attempt to retard the timing just brought it back into the approximate neighborhood. But that's not a long-term solution.

 

Just getting back to this...Still have the KS code, but there still doesn't seem to be any issues with engine running at highway speeds(60-65MPH) on 31" tires although there is a 5 mph discrepancy in the speedo. Gas mileage, using the ethanol blend here in NY is around 16 - 16.5 MPG. engine timing, as checked by my regular mechanic is spot on at idle and highway speeds.
in the meantime I also contacted my cousin, a former Toyota Service manager and author of a software program for Toyota dealer ships, and inquired regarding the Check Engine light and lack of symptoms. His recommendation...put some tape over the light. While this seems a bit far-fetched I don't know what else to do. It does appear that while the code is showing, there are NO engine operating symptoms.
Thoughts, comments, concerns? Should I just leave well enough alone?

 

Flywheel issues - loose, missing teeth, etc., and other clutch / tranny issues, can be transmitted to the KS, in GM's that I know of...

 

There are performance issues, if you get the problem solved and get rid of that code you will see a difference in power and mileage. With that code the ecu keeps the timing a base, no advance at all. I worked through code 52 on my 90 pickup, and it took a while. First I replaced the pig tail, that didn't get rid of it, it would still return once in a while. Next a Toyota knock sensor. I was sure that would take care of it, but I still had the problem now and then. I figured it had to be the wire between the pig tail and ecu. I ordered some shielded cable of the net, ran that from the pig tail to the ecu and its been a couple of years and no more code 52. The wiring harness looked fine, my pickup looks almost new, so you cant go by looking at the harness. I guess the shield in the wire was broken at some point, I don't know but the shielded cable seems to have done the trick. Hope this helps........

 

Even if that were true, it couldn't cause a code 52. It might lead to performance issues (retarded timing), but BigBoox says that is not the problem.

 

Ok - if not, then exactly how so is it not what's going on? Bigboox???

On GM, KS test is tapping a screwdriver handle on the motor [head] right next to the KS itself. If the motor stumbles, KS is operating properly. If nothing happens, then KS is already in operation, changing timing to closer to 0 TDC - retarding timing, to stop the valve knock, because that's what it does. If something else is causing a 'knock', KS doesn't know the difference, and starts its' job. I bet the test is identical for Imports

As far as a Toyota Service Manager saying to put tape over the DTC Diagnostic Trouble Code Service Engine light, well, I think that's pretty FU service...

Just my .02; take it or leave it................................................ ..

 

I don't know anything about GM knock sensors, so I'll take your work on that. But I doubt that "test" would work on a Toyota. For starters, you can't access the Knock Sensor with the engine running; it's buried under the intake manifold. You can bang on the intake manifold or the head all you want and it won't make any difference.

More importantly, the Knock Sensor is sitting on top of a block of steel with explosions going off 200 times/second, and yet it ignores all of those. How? It's tuned to a specific frequency http://www.autoshop101.com/forms/h38.pdf So I'm pretty confident that it would have no trouble ignoring screwdriver handles and transmission vibration and so on.

There's no published test for a knock sensor, and I haven't heard of any that really work, short of using a go-nogo test with an oscilloscope. There may be a workable test, but I'm pretty sure a screwdriver handle isn't it.

 

"As far as a Toyota Service Manager saying to put tape over the DTC Diagnostic Trouble Code Service Engine light, well, I think that's pretty FU service..."

Schrade, He was a SM in a previous part of his life, now retired, and he did write a software program for Toyota service departments, He was made fully aware of the Hx of my truck and he agreed that it may well be possible that the CEL is malfunctioning. As I stated, There is NO limp mode going on, truck runs fine at highway speeds as well as around town. Two different mechanics have run the truck, in a variety of actual driving situations with a scope attached and there were no mechanical/electrical problems noted. If there are no timing changes being noted, no rough running, stumbling etc., I'm of the opinion it is a fault of the computer, so the tape idea works for me. And gas mileage is improving since the rebuilt was installed, 3500 miles and it's now getting about 17.3 mixed highway and town, with 31" tires. (5 mph lower than actual speed).
I'm actually not complaining about the truck at this point, just posting to pass along a different take on the code 52.