Hey folks, I'm really struggling with the 3VZE in my 93 pickup dually, so I figured I'd see if I can get some guidance here.

I bought this truck with a blown head gasket and replaced the heads with rebuilt ones. I also replaced all the parts I could along the way; gaskets, timing belt, water pump, radiator, knock sensor, spark plugs, plug wires, injectors (Precision Auto multiport upgrade kit), and a few things I'm sure I'm forgetting. I also did an EGR and PAIR delete, and piped up a crossover delete with Yota1's plate kit.

When cold, the engine has a little trouble starting, but then it *appears* to run fine with an initial idle somewhere in the neighborhood of 1500-1800rpm (when warm it has no trouble starting). It'll run like this until you rev it a bit, and then the idle drops down to 800-1000rpm and starts running pretty rough, and smelling VERY rich. If you rev it up, it smooths out and seems less rich, but always drops back down to that rough lopey rich idle.

What I've checked/replaced/ruled out:
- Ignition timing (set at 10°BTDC)
- Spark (wire pull test)
- Distributor (cap and points are clean)
- Replaced throttle position sensor and calibrated
- Replaced O2 sensor
- Tested cold start injector for leakiness
- Verified no vacuum leaks
- Tested air flow sensor per FSM
- Cleaned intake manifold (sea foam)
- Compression tested cylinders
- Put new premium gas in tank (added sea foam too)
- Adjusted idle (doesn't get better no matter how high or low I adjust)
- Reset ECU multiple times to force relearn

At one point I had codes 21 and 41, which is what prompted me to replace the TPS and O2, but they went away when I replaced those parts.

I'm 100% convinced it's not an ignition issue, so that leaves fuel and air. My only two remaining guesses are either valve timing (I'm gonna pull the timing cover tonight and see if it's off), or the upgraded injectors (I have no idea how to go about testing this).

All help, ideas, thoughts and prayers are greatly appreciated 😂

 

Don't forget to check the Idle Adjust Screw's o-ring. It gets old, and brittle, and can drop chunks down into the air passages below the screw. Can cause all sorts of interesting idle difficulties.

You mentioned that you adjusted the idle all over the place with no change. Are you sure you were adjusting the Idle Adjust Screw, and NOT the cover cap screw on top of it? Not that *I* would ever do something like that <ahem>. I mean no insult. It can happen to people not familiar with the Toyota Throttle Body set up.

The Idle Adjust Screw's o-ring is readily available everywhere. Hardware store, auto parts stores, etc. It's a very good idea to rub a thin layer of Vaseline or silicone dielectric grease onto the o-ring before installation. Not only does it make the rubber last a LOT longer, it makes for a better seal.

Have fun!
Pat☺

 

Interesting you mention this! I spotted this advice somewhere else in the forum (maybe from you). However my idle screw doesn't have anything I'd call a cover? Maybe I'm missing something.

I did actually pull out the screw last night. Long brass dealio similar to what you'd find in a carburetor. I cleaned some gunk off it and observed that the o-ring was hard as a rock, but intact. I will definitely pull it back out and replace that o-ring now that you mentioned it, but I don't think any chunks came off.

Thanks for the advice!

 

Idle control valve my be dirty and sticking.

https://www.bing.com/videos/search?q...BD17&FORM=VIRE

 

OOH! This very much sounds like it might be the/an issue. I will look into this and report back.

 

Well I set about pulling apart the IACV. The threaded bit on the top of the valve was completely stuck and required some persuasion in the form of heat, penetrating oil, and quite a bit of hammering to get out.

Once I was able to get it apart, I really couldn't see anything functionally wrong with it, and all the parts were pretty clean.

HOWEVER, I discovered my throttle body coolant passages are completely cemented full with what I can only assume is dried coolant gunk. Chiseling it out with pokey tools hasn't really made a big dent, so I'll try soaking it in chem-dip or something, but I'm guessing I'll need to just replace the whole throttle body.

 

Update: I'm no closer to solving this.

I replaced the plugged throttle body with a salvage one. I checked the IACV before installing and everything seemed to be fine. After installation, nothing changed, still idling rough and rich.

One of my friends brought back up the O2 sensor being a potential issue and so I ordered another (a proper Denso unit this time). I also ordered an ECT sensor and fuel pressure regulator while I was at it.

I just finished installing all three and there's still absolutely no change.

Next I'm going to check the fuel pressure and also see if I can check the fuel trim diagnostic voltages again.

Any suggestions would be greatly appreciated.

 

SOLVED!!
I can't believe the issue was this simple.

So on top of the AFM is a plastic cap that's sealed with some silicone. Someone had clearly been in mine so I took it off to have a look and maybe advance the AFM spring a bit.

Turns out the clips had broken off the cap causing it to droop and interfere with the swinging part of the AFM. When I revved up, the swing would move out and then catch, making the ECM think the door was still open, thus inducing a rich condition.

I'm going to try and make a new cap to fix this, but with the cap off the issues are completely gone.

Thanks everyone for your help. Hope this helps

 

Where is the AFR sensor located?

 

I believe he means the VAF (Volume/Vane Air Flow meter). Located above the air cleaner.

And just in case you're thinking of messing with it:

 

Yes this is exactly what I mean. It's mis-named a bunch on the forums and I guess I got my head all messed up.

To build on those photos; if you think you're having the same issue as me, you can just GENTLY take a razor blade to the silicone around the outside of that D shaped black cap, and ease the cap up with a screwdriver. However be gentle, as all the delicate bits are underneath.

 

AFR usually means "Air-Fuel Ratio." While the O2 sensor kinda does that, AFR usually means a low-gain sensor to contrast it with a high-gain conventional O2 sensor.

The mis-naming is often when someone calls it a "MAF" (Mass Air Flow) sensor. Different technology. But you can call it an "AFM" (Air Flow Meter), and while less specific you'll at least always be correct.

 

I have also since prototyped a 3D printed replacement for the cap that goes *over* the lip, instead of inside. Here's some photos.




I'll link the STL files soon, just been busy. So far the cap fits excellent and has even stayed on without adhesive in my prototyping. Though I recommend using silicone or something to seal it up completely.

I would also recommend printing this in ABS, as this part does get very hot inside the engine bay. Standard 3D printing plastics like PLA won't stand up to the heat very well. My final version will be printed in ABS.

 

Here's the STL file for the replacement cap. Hope this helps someone in the future!

https://www.thingiverse.com/thing:5917488

 

Had the same problem with my rig a while back. Failure to plug it back in properly will lead to your engine running rich with poor idle and dying after giving it some gas.
I've seen multiple threads on here where the VAF was the culprit. Glad you got it figured out.

 

Thanks for the good info and pictures. I'm trying to figure out why my rig idles fine but will stall out when I place it in gear after a cold start.

 

The 3D model is finalized! Here's the link if anyone wants to print their own:
https://www.thingiverse.com/thing:5917488

Cheers and thanks to everyone for their help! Hope this helps someone in the future.