Is this throttle body supposed to do this?

So some history, my 2001 4Runner had a problem starting (it cranked no problem), and I saw a MAF code, so immediately thought that was it. I replaced it with one from Oreilly's, I forget what brand but I know it wasn't Denso (more on that later).

Well that got it to start now, but it wouldn't idle, any RPM below 1000 and it would sputter and die. So I bit the bullet and replaced the entire throttle body with a new Aisan throttle body.

Now it starts and it idles, but is giving me a Bank 1 Too Lean code P0171. So I did a smoke test to find any vacuum leaks. The ONLY place I saw substantial smoke from this test is coming from the throttle body itself where the Accelerator Pedal Position Sensor is. I removed the throttle body to take a closer look and there is an opening on the bottom side, that's where the smoke is coming from.

My question is, is this normal? I'm leaning towards not normal but I don't know for sure.

I can't find any other vacuum leaks that would make my engine run lean, other than the throttle body, but if it's not supposed to leak in this spot, I think I can return it as defective. My other suspicion is since the MAF isn't Denso, it is O'Reilly part #MF4226N, Blue Streak Electronics MAF Sensor, that it isn't properly calibrated? One of these two has to be causing my "too lean" code, unless someone can think of anything else. I'm initially ruling out an injector issue as I think that would cause a cylinder specific code like a misfire.

I went ahead and ordered a Denso MAF, they're only $85 from RockAuto.com, so figured might as well eliminate that variable. Should arrive in a couple days.

Anyway, here are some photos to show where the smoke test identified the leak on the throttle body.

Thoughts?

 

Does the old throttle body have that same hole?

If so put it back on and see if the smoke still comes out there, I know of no other way to see if the new one is defective other than that.

 

Pull the maf and look for an o ring.

Might be missing or pinched.

 

How much was this TB? Is it new? It looks rebuilt. I'd return it and get a full brand new one straight from TOYOTA. TOYOTA's prices dropped on these and I think they were like $450 last time I checked from McGeorge (now Ourisman).

Regardless, I agree with you, you can't have smoke coming out of that or you have unmetered air. So compare the old one. Put the old one on and see.

 

Turns out, looks like I tossed the old part already, but in lieu of putting the old TB back in, I just covered up the (weep?) hole in the new TB with some foam tape (double sided tape where I left the cover on one side), and saw no difference in my AFR and FT readings.

And my new Denso MAF arrived today, so seeing as I have NO vacuum leaks but the PCM still thinks it's running lean, I quickly swapped in the new Denso MAF.

WUT!?!?!?! Seriously, the change in the readings was instantaneous!!! So I'll admit it, I was skeptical before that electronic parts like this need to be OEM, but ya, this made a believer out of me. ALL of my AFR and FT readings are now back to looking like normal operation, the motor runs smoother, and it idles perfectly.

So I'm sure many here already believe it, but ya, I won't bother with other cheaper third party electronics for my 4Runner from now on, its just not worth the hassle and I didn't really save any money since I had to buy another MAF anyway. Lesson learned (the hard way!)

 

Awesome!!!!

A little more advice: NEVER throw old parts away until you've driven a month. It takes that long for codes to show up. You also may forget to move a part from one part to the other.

 

Update: Well dang, I thought I had solved the problem, but only partially evidently. When I'm driving, the FT's look normal-ish, my LTs are a little elevated but my ST fuel trims chase zero pretty much. But at idle, I see both the ST and LT FT's shoot way up, and then the MIL comes on again with the P0171 Too Lean code.

I'm thinking a small vacuum leak in the system still would cause this because the volume of air leaking in relative to the amount of air metered by the MAF - at idle - is larger than when I'm driving and a much larger volume of air is being metered, so the leak isn't as noticeable, and maybe that explains why the LTs are just a little elevated?

So now I'm back to wondering if my TB is causing this small vacuum leak again? The smoke test didn't show any smoke coming out anywhere else from the intake side. Whew, I thought I had competely solved this issue!

Here's some scanner screen shots of the Fuel Trims to show what I'm seeing. The left one is while driving, the right one is while idling:

 

One trick is to do the brake cleaner spray trick. Or use most any flammable spray. Spray around the engine\TB while idling and listen for changes in the idle. If there is a vaccum leak, it often pinpoints it.

 

Well folks, I realized I had neglected to update the progress on this issue. Short version is all vacuum leaks have been eliminated and everything is working fine!

Longer version, the last vacuum leak was on one of the small vacuum hoses that connects to the back side of the bottom intake manifold, joined by a 'Y' hose connector, that eventually goes to the Throttle body. They are practically impossible to inspect with the upper intake plenums on, so once I found out there are those vacuum lines there and taking the intake plenum back off, I was able to remove and inspect those hoses, and one had a rather large crack. Replacement was easy, reassembled the intake plenum with new gaskets, and that did it.

So now all my Fuel Trims and Air Fuel ratio readings are practically perfect now! Been running for several weeks and the LT's are almost zero, the STs are zeroed, and the AFR reads perfect at ~3.9-4.0 VDC at idle.

So, don't want to discredit any tools, but the smoke generator tool didn't help much in finding this leak, maybe because there was a "cover" hose on the vacuum line that had the crack? But spraying carb starter spray around the back side of the intake gave me an instant change in the O2 and STFT readings so I knew the leak was somewhere back there. Finding exactly where the leak was came down to actual visual inspection. I was pulling my hair out for a while, not realizing those vacuum lines are there.

Anyways, thanks for reading, hope this helps others with the same type of issue.

Edit: BTW, the weep hole in the Aisun Throttle Body is not affecting the air fuel ratio at all, even though there was a trail of smoke coming out using the smoke generator. It could be that under vacuum that weep hole seals normally? But also wanted to clear that up as well. The new throttle body performs good as new.