Chronicles of a High Idle Post Tune-up

I'm not familiar with that throttle body, however from other engine's use of bellows, I know that they're usually used to make adjustments for atmospheric pressure changes.

In this case it may be used for adjusting the idle to the ambient pressure.

 

Quick update: I swapped the throttle bodies and the idle was a lovely 650-750. The hesitation persisted in the mid 3K's at full throttle in any gear other than 1st. I'm going to swap the IAC's tomorrow to see if I can just trade that one component out instead of the whole throttle body. I'll give a more in depth analysis tomorrow.

 

As promised, better analysis:
1) the lack of complete closure of the butterfly is not abnormal, my wife's 4Runner has the same situation and my truck idles fine with her throttle body.
2) for anyone who's tore apart the IAC, the valve may seem to be "stuck" open a bit and not close entirely–again, this is normal, both throttle bodies exhibit it.
3)@badbrains, I think there is another bellows on the back side of the throttle body (present on both of mine) that performs the ambient pressure adjustment function, but I sincerely appreciate the proposal. Whatever the function of the 2nd bellows on the front of my throttle body, it's not very important because my truck ran fine without it.
4) a 99 AT TB will work on a 01 MT, but not without linkage modification. The bracket that holds the throttle cable in position is too far away from the older TB linkage and it will keep the throttle 50% open all the time. Fortunately, I had a fabricated piece of aluminum lying around from the old TB spacer I pulled off that extends the aforementioned bracket out, allowing it to just barely work if you max the throttle cable nuts out. Along with this, your cruise control cable will be full of slack and look ridiculous, but it does still function.
5) I OHM tested the TPS, MAF, ECT, and the 3 right bank injectors while I was there. MAF & ECT checked out. Injectors were high but all consistent, so residual engine temp was probably the culprit because they were close to the right value (15.7 vs 13.8 IIRC). TPS changed resistance smoothly, but the range was low (.78-2.7 vs 1.3-3.2 IIRC). Heat should raise the resistance, not lower it. I'm not convinced this is a problem, but I'll keep it in my differential.
6) I'm open to suggestions concerning the mid-range hesitation in higher gears. Possibilities currently in a particular order are: a) injectors that might not be flowing well. An Ohms test won't help with this. b) O2 sensor might need to be changed, although it "looks" fairly new. c) TPS sensor could in fact have a "dead" spot in it. d) one coil pack might be shoddy. e) crappy rings causing oil blow by fowling a plug already? (unlikely).
7) Also open to suggestions about the hard hot start. Now that the ECT spec'd out, I'm pretty clueless. None of the above would likely cause that and not cause a hard cold start.
8) Both my wife's and my upper plenum had standing oil in them...we both have new PCV's and cleaned TB's and plenums (I did her's about a year ago IIRC). Her throttle body was filthy also. I think the culprit is the vacuum hose on the intake tube that enters right before the the TB. It comes straight from the left valve cover with no apparent valve. I think I need to plug it and put a PCV breather on the hose. I searched this with limited success, don't really know what to call that tube. Manuals refer to it as the "Emissions Hose" I believe.

Sorry for the lengthy post. I'll report back later after I swap IAC's.

 

I think your hesitation issue will turn out to be the TPS has a "bad" spot in it. that's usually what regular repeatable hesitation issues turn out to be. it might be injectors but they usually cause issues in most of the throttle range and not just one spot.

were you able to get a replacement TB? I didn't see you mention if you did or not?

out of curiosity, did you clean the throttle body with carb cleaner or soak it in some to clean it? maybe you stripped of the coating inside it and that small difference in butterfly clearance is just enough to cause the high idle

 

I haven't purchased a replacement throttle body yet. I'll probably do it later this month. I priced them on eBay for about $100 for an AT model...$750-917 new.

I didn't soak the TB, just sprayed and rubbed mostly carb cleaner and a little bit of brake cleaner when I became inpatient.

You are very astute with your TPS suggestion! I decided to follow the advice of an older, wiser mechanic (dad) and check for codes incase the CEL bulb was out or it just didn't set for some reason. This is what I got:
1) P0171 bank 1 too lean (I'll have to check which bank is 1, I forget)
2) P0120 TPS/pedal position sensor A circuit malfunction (10 points Keaker!)
3) P0505 idle control system malfunction (just as I suspected!)
4) another P0171 bank 1 too lean

I think I'm fairly safe in assuming that code 1 is caused by codes 2 & 3. I reset the codes, drove home and the only code that was reset was 1. Still no CEL?!?!

Anyway, I just priced everything and I can get a new TPS for $36 shipped. I can get a used IAC valve for around $85 used or $200 new. I'm considering this route over the entire used throttle body just so I don't have to fight with linkages and as much will be stock as possible on the Taco.

Thoughts, suggestions, and vitriolic criticism are all welcome. I'll post whenever I get around to testing the wife's IAC valve on my truck.

 

Swapping the IAC valve did indeed fix the idle. I also tried it with the TPS swapped, but no help for the hesitation. Sorry Keaker your points are revoked.

Even with these things switched, the P0171 code was set again. This makes me pretty darn sure that the throttle body has nothing to do with that code or the hesitation. I think it's either MAF or O2 sensor. I hope it's not crapped-out injectors, but that's still a possibility.

Now I have to track down a nice used IAC valve and lube up the drivetrain. Then I'll start closing in on that hesitation and the hard hot starts.

 

that's ok, im glad you fixed it.

I just replaced my injectors to try and solve my rough idle and slight stumble/hesitation issue from 1500-1750 rpms and it runs a little better with the new injectors with a little more pep I "think" but still idles rough and still hesitates.

I just ordered a TPSs and IAC valve and will swap those out and see. I already did new plugs and wires and cleaned TB and EGR valve (IAC too)

I do see a lot of 5vz engines with injector issues so you probably have a little bit of everything going on there including bad injectors

 

Maybe do a round of Seafoam, then change your fuel filter for that mid-range stumbling.

 

Both good suggestions but I did both of those 2 weeks ago.

 

I'm really starting to think the hesitation and hard hot start are both caused by the MAF sensor, even though its ohms are spec. That would set a lean code. I'll swap my wife's MAF with mine when I get home and see what happens. Having 2 3.4's next to each other is awesome!

 

i will be watching, if the TPS and IAC replacement doesn't fix mine, the only thing left not replaced is the MAF for me

the hesitation improved "slightly" with the new injector set but its still there and I am very hopeful the rough idle will be gone after replacing the IAC like what happened for your idle issues.

 

Success!

Plugged my wife's MAF sensor in and all of the sudden I had a different truck. I couldn't keep it planted in 1st! I actually burned rubber on dry pavement from a roll in 1st with the backend locked. Hesitation was 75% better. A slight shudder was still present.

I got home and plugged in the scanner and all was well. Before I put mine back in, I cleaned the heck out of it. I used the technique illustrated below and I even got brave with a Q-tip (what's the harm if I'm going to replace it anyway?). I drove around a bit and checked for codes. All clear!

So, what's the remaining stutter? I don't think it's all drivetrain because I can hear the engine rise, drop, and rise immediately with no further hesitation. No loss of power at any point, just when I drop the hammer all the way it's up, very slight down followed by up all the way to redline now. I'd almost call it bad throttle response since it's only at the initial pedal press. Is this possibly normal? Am I expecting too much out of a 200,000+ mile truck? No longer stutters in higher gears, just mid RPM range when the butterfly opens 100%.

Remaining checklist:
1) Lube drivetrain and change fluids down there
2) Fix check engine light bulb (or put one in if it was removed intentionally)
3) Maybe an O2 sensor? (my 2nd tank full was 16.4, very pleased!)
4) Change the coolant too. Not relevant for this thread but might as well list it. The last dumb dumb was nice enough to put something yellowish in there as opposed to toyota red.

Edit: I'll blame the MAF issues on K&N. I definitely wouldn't have put it on there, but I bet it was the cause of this filthy sensor.

 

Oh, hot start seemed slightly better. I need to try a few more times to confirm though.

 

and you were getting good "readings" from the MAF sensor before you swapped them?

if so then I might be replacing mine soon if the tps doesn't cure my hesitation.

as to your delay in throttle response, I think that can be explained by just computer reaction time is slow, after all its a 15 year old computer system.

 

Yes, my resistance was to spec on my MAF. I think the problem is that the sensor is functioning fine electronically, but it's so immensely dirty that it doesn't detect that actual amount of O2 in the air because of physical limitations. This give you low fuel input to match and the O2 sensor let's you know it's lean.

 

hmmm, because mine read ok too and it "looked" clean but I cleaned it again anyway and had dismissed it as a serious contender for the problem based on that

 

Did you look at the 2 wires way down in the central tube? They're really hard to see, you need to hold it just right with a light behind you. They should be white, not black.

 

Just an update:
-Hard hot start is almost entirely gone and getting better
-Initial-drop-the-hammer-stutter is also less pronounced
-Idle is now around 850 after 1 more IAC valve cleaning...still will probably replace for that 100 rpm

My truck seems to drive better everyday.

 

so I guess the ecm just needed time to reset your adjustments now that its working better.

are you going to tell the wife her 4runner stutters now for some unknown reason lol

but seriously, has all of your bad symptoms transferred over to her 4runner now?

hell I can hardly see good enough to read this forum but i'll try lol

if you are looking for the IAC I found this was the best price I could locate and it looks exactly like the oem: http://www.amazon.com/gp/product/B00QU888HS/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

 

Haha, I told her my truck needed the good parts worse than her 4Runner but she didn't buy it. I actually never installed any of the Taco's stuff on the T4R, I just stole parts, took it for a test drive, and put them back on the T4R. I guess installing them on a working vehicle would have been the most scientific way to confirm their need for replacement, but I got lazy.

Also, that's by far the best price I've seen! Thanks for the link!