Forerunner

Howdy everyone, from sea to shining sea,


I have a couple of issues with my 1990, 3VZE, automatic 4x4 4Runner that I think are related, but may not be.

First issue:

When the truck idles at about 900 RPM on stock tachometer, with gear in Park, when I put it in Drive, it drops about 400 RPM, down to 500 RPM. It does the same for reverse or any gear. Drop this large seems abnormal to me, so something has to be wrong. I am used to seeing about 200 RPM drops at most on various automatic transmission vehicles, or no drop at all. But 400 RPM makes me wonder what may be wrong


Second issue:

The truck does not always idle at the same speed, in Park or in Drive. The idle does not fluctuate over a short period of time. Rather, in Park it may idle at steady 700 RPM, then, the next day, I may see a steady 900 RPM, or anything between 700 and 1100 RPM. Always steady, never stalls. The same can happen when I drive for a while. Before driving idle in Park can be 1000, after an hour 700, or anything in between. The only common trend is, which is normal, for it to idle higher when it is cold until it warms up, then it drops some. However, once I put it in Drive, it always drops 400 RPM, so if I run 1000 RPM at idle that time, it goes to 600 RPM, if I run 800, it drops below 500 RPM. Never stalls in drive either, but as you can imagine when it gets 500 rpm an below it starts idling a bit rough. Not very rough though.

I have taken care of tune up, plugs and wires, and a few other things. Among them, and that is not all inclusive list, timing belt replaced, timing was set, TPS tested, AFM/MAF tested, fuel filter replaced, air box cut, idle adjustment tried, 02 sensor replaced, Fault codes checked, found none and K &N filter installed. The idle issues never changed, the truck acts basically the same since before I did all of the above. I am out of ideas as to obvious causes. I cannot explain the drop when placing it in gear either. My guess is some component or valve that is supposed to idle up when placing it in gear is mailfunctioning. I am really hoping that the two issues are related, so I can whack them both with one hammer, so to speak. It has been doing it for a while.

Any input and ideas for where to look greatly appreciated!

nunsa

I had the same prob.'s with mine, even though I have a 5speed. What worked for me was: I pulled the idle screw out, all the way, it was caked w/carbon thicker than my wife's mascara! You have a big idle drop which is not normal! I also sprayed carb cleaner into the hole where the idle screw goes. You should also grab the old toothebrush and start scrubbing your t-body plate..! Even though you speced your tps out, it gets crudded w/carbon - remove the tps and give it a good cleaning, don't use carb cleaner as it will deteriorate your tps. Another thin to try is some SeaFoam, pull a vac hose off and suck it into the engine, I prefer the "P" line from the purge canister, I attach a longer vac line from the T-body where the "P" line goes and allow the vac to suck in the SeaFoam. Allow the engine to "sip it in" as too much might cause you engine to hydrolock! IMPORTANT! Also make sure you have no air leaks at your air intake nor vac leaks! And after you decide to run some Seafoam, pull your efi fuse so that your computer can relearn itself!
Good Luck!

Bumpin' Yota

Mine does that too, but I assumed it was from the additional load of the tranny/drive train.

However the startup idle WILL vary according to the engine coolant temperature. It does this through the ECT sensor. When cold, it has a high resistance and as it heats up, the resistance drops until you hit your 190odd degree temp. Typically when the ECT sensor has a high resistance your timing is advanced a bit and your engine runs a bit richer. You may also notice that the engine has a lot more power when cold. This is were the ECT mod comes in. (Do a search and you'll find TONS of info on this mod.)

Forerunner

Thanks for the replies. I have something else going on as well. First, I cleaned the screw. It was not bad though and made little difference. I also used Seafoam in the throttle body per instructions on the can. Maybe it helped some, maybe not, I am not sure. The truck was running well before, and is still running well. Here is what else is happening.

When in PARK or Neutral, if I smoothly apply accelerator from Idle, the RPM rises smoothly to about 1400 and I can hold it there, no problem. If, however, I continue to apply the gas pedal, the RPM actually DROPS to about 1300 and lingers there, with noticeable, but not huge, roughening of the engine. If I continue applying the pedal, the RPM kind of stays at 1300 for a little bit of additional pedal travel. Then, all of a sudden, at some point during additional pedal pressure, the RPM just goes smoothly but quickly from 1300 to about 2500.

It is like there is a sudden inflow of fuel, air, or boost. From that point on, above 2500, the rpm varies in direct proportion to pedal pressure, no more funny stuff. If I let it drop below 2500 rpm, it again goes straight to 1300. In effect, there is no way I can hold anywhere between 1400 and 2500 in any pedal position. All of this is in Park, of course, there is nothing of sorts going on in Drive. The truck runs smooth, accelerates fast, gets to 85 MPH+ easily and with no hesitation.

I am not suprised I have not noticed this, because how often do you rev up RPM in Park for any reason? I just did it after Seafoam application to clear up the engine. That is when I noticed it. So I have no idea how long it has been that way.

I will try to draw some sort of a linear graph, with application of gas pedal corresponding to the RPM:


RPM in Park
--------------------------------------------------------------------------
700 smooth rise to 1400 drop to 1300 1300 1300 instant rise to 2500


PEDAL APPLICATION - continuous rising pressure from idle
--------------------------------------------------------------------------
........................................|no RPM change zone|................



Well, this post feels like it is long enough. Any ideas?

Forerunner

Thanks for the replies! It was the TPS - it was out of adjustment in the way it was mounted to the throttle body. You know how the top of the TPS screw hole is shaped like a groove so you can rotate the TPS a few degrees this way or that. After searching through factory manuals (more like being lost in factory manuals) I decided to give the TPS another go. There were no codes for TPS in the ECU. I figured I would exhaustively test it in every way possible anyway.

That task was made more difficult by the fact that the factory test procedures assume that, at least for some tests, you have the throttle body removed with the TPS mounted to it. Took me a long time to figure it out, by looking at the pictures in the manual and not being able to match them to the actual truck, that the pictures were of the throttle body but upside down!!!

I got the TPS off which was not easy, considering the stupid way the screws that mount it are positioned. Tested it and it was fine. Mounted it back on the throttle body, tested it as procedure calls, by using thickness gauge.. then adjusted it according to the same procedure. Behold, that took care of the problem. Now revs up smoothly and the idle is also smoother than ever.

All the more weird, considering that the TPS was mounted maybe a degree or two differently before. I find it hard to believe that 1 degree of TPS rotation would make this much difference. If you have tried adjusting TPS on 3VZE you know what I mean, it is not a fine instrument. I have replaced TPS on many a vehicle before, and I never seen one that was so picky about how TPS is positioned. Heck, some of the TPS did not even have any adjustments in the way they were mounted.

The moral of this, at least to me, it is not enough to have a good TPS. It is not enough to mount it correctly in the right holes. Once has to adjust it precisely, and I mean precisely (it took a hair of rotation to make TPS readings show within spec vs out of spec) and you need thickness gauge just in the right place to do it. Dang I would much rather work on 22 RE engine

Another thing it seems that ECU diagnostic algorithms for the TPS are really useless, or at least incomlete and unable to determine out of spec parameters. I mean, I was driving with a TPS that was giving out of spec readings and made the engine behave so weird..yet there was no code for anything in the computer. Just shows ya one cannot assume anything with these older motors. Thats about the only thing our 1996 Doodge has on these older Toyotas, better onboard diagnostics (OBDII)

I have not yet measured my gas mileage since the repair. I reset the ECU after adjusting the TPS so we will see.. just eyeballing the gas gauge though, it seems that gas mileage has marginally improved.