Throttle Body Adjustment

have my truck running after doing a frame swap and at idle it is at 1800 starting and then down to 1300/1500 rpm. I took off the Throttle Body (TB) assembly and cleaned everything (IAC,...) but there was light all around the butterfly.

I adjusted the screw on the back side (toward firewall) of the TB so that it was barely touching - I can slide paper between the adjustment screw and plunger - and I adjusted the one in the front which I think is just a dampener. After the adjustment I dont have very much light passing around the butterfly but is setting this okay? what is the adjustment on the back for?

front side:

 

Interested as well

just cleaned and removed TB/intake manifold/plenum

while searching, found a thread were guy worried about gap between butterfly valve and TB housing
Another member posted pix of a brand new oe TB out of box, was the same gap per flashlight test
I would not worry about it

when I cleaned TB/IAC, I saw black sensor that had slotted screws for some sort of adjustment (had tht factory paint on the screws just like in your pix)
I didn’t touch mine
But still interested what Gurus say

 

Ha! Found good pix of the slots

 

Op the top pic is the dash pot. It normally has vacuum on it and is retracted while the truck idles, no engagement with throttle plate. So your adjustment with throttle body off and dash pot plunger extended (no vacuum holding it back) isnt really gonna change throttle plate position nor idle rpm with truck running. In other words, the dash pot with no vacuum on it will make throttle plate open slightly. You can search for a good explanation of what the dash pot does, more for rpms when shifting I think. No idea on the second pic, my truck doesn’t have that, just a throttle plate stop on my 2.7 l 4 cyl. Idle probs seem to be usually air related outside of throttle plate issues for most. So vacuum leaks in hoses, gaskets or stuck IAC more often the culprit but can still be other stuff (less often). Research here a bit first.

Control car,
That’s the TPS (throttle position sensor). It’s just a rhoestat that tells the ecm what position the throttle plate is at, position 10 at idle and 70 and full wide open throttle. Basically ecm learns what is closed and full open even if you have TPS set slightly wrong, those slots dial it in for the 10-70 setting fine tuning.

 

ControlCar : were you cleaning to solve a high idle issue? if so, did it work?

Thanks THatt, Ill set the screw back to the original position on the dash pot, maybe check it with vacuum to see if its working. Ill research how to track down vacuum leaks.

 

How do I bump my slow idle speed up on my 2.7L?

 

Ah, you have the slightly rare throttle body like mine, where the two springs attach to that metal pole, instead of one spring attaching to the dashpot bracket. I notice that if I push the dashpot plunger down towards that bolt that contacts the plunger, I can get my idle to fully drop to...idle. But I don't think it's my high idle problem all the same. I can get the same effect by pushing against the throttle linkage. I thought maybe the plunger was getting sticky but after lubing and working it, there was no change

My understanding is that the dashpot keeps the rpms from dropping too low when you shift on a standard. So auto transmission trucks don't have them. There's a guy here who ran without his for a while and noticed no problems. I DO think that if you adjusted that bolt up, to where it was starting to push the plunger in, that would raise your idle. But unless someone already did that, I don't think loosening the screw will drop your idle. I actually didn't know there was any adjustment point on the throttle body...other than maybe tightening the throttle cables once in the the truck's life.

You can also find a lot of posts around here on cleaning the throttle body and IAC...cleaning my IAC is what started me down the "high idle" problem road. I had cleaned the throttle body itself in the past and noticed no difference one way or the other. I'm no expert, but what some people say makes sense: the throttle body gets worn over time. Often, not always but often, the carbon buildup on the throttle body itself and the IAC mask the wear. Then someone reads a thread about cleaning them, sees that it's a pretty basic job, and goes to town. Throw everything back together...high idle! Now that the carbon is cleaned up, the wear shows itself. Sort of like a high mileage truck that's run conventional oil all it's life, then someone decides to switch to synthetic. All the gunk built up from all those miles is actually masking failing oil seals. The synthetic cleans up the gunk, all the seals start leaking...

 

I went through the same stuff with my 98. The dashpot is like what MT-98 explains. I actually ran a TB from an automatic that didn't have the dashpot on it with no ill effects. Sometimes when you clean the throttle body around the throttle plate it cleans the gunk around it that kind of closed off that slight gap. Although my e-bay find worked I had to modify my throttle cable position. I don't have cruise control so it wasn't too difficult. I ended up sending my old 200K mile TB to maxbore and I am glad I did as he does phenomenal work. Pickup idles perfectly now with no problems at all.

Side-note. I have (2) IACV one of them the inside piece didn't move as freely (rotates around) and sometimes would stick causing high idle. Replaced with a used one where the cylindrical door piece moved a lot more free and no problems at all.

 

I tested the Dash pot - moved fine with 5-7inHg, open about 1/4" at 12inHg. Not sure how much vacuum its supposed to get. The truck only has 100k so I dont think it should have too much wear but maxbore may be something I could do. I am going to pull off the IAC again, I dont remember any moving parts inside.

 

The vacuum dashpot is to slow the throttle closing… a high vacuum during deceleration will pull oil vapors into the intake, this is strictly an emission thing. Adjust the throttle stop until you can feel it bind in the bore then add a little more to keep it from sticking. If the bearings/shaft is wore and the plate does not sit in the same place every time it closes, thats a problem.

 

Just a guess but maybe your IAC is gunked and stuck closed.

 

Makes me wonder if improperly adjusted dash pot could be causing all these gunked intakes needing cleaned and resulting thought a catch can is needed. I will dig and look but does FSM tell how to properly adjust dash pot setting? Asking since it seems you may know. Thank you

 

Just tested the IAC watched
https://www.tacomaworld.com/threads/iac-valve-testing-and-cleaning.646710/

everything is moving good. Ill put it back together tonight and see where its at.

 

I cleaned my IAC, gave me a high idle. So I bought a new one. Higher idle. Put the old one back on and it went back down to the previous high, but less high than the new IAC caused. I've kind of gotten used to it. But it's still a project on my list.

 

I assume you are disconnecting the battery when doing this? Doing this helps in the idle relearn. I’d drive it around after you put it back together for a bit. It shouldn’t take that long but the idle should drop back down.

 

Check the throttle cables to make sure they aren't too tight.

 

Answered my own question for dash pot (throttle opener) setting. See below if interested.

 

@THatt - So if no vacuum to throttle opener then expect 1200-1500 rpm idle? I wonder why they suggest replacing the throttle body and not adjusting the set screw?

my idle is around 1500, I tested the opener with vacuum pump and it is working, so I must not have vacuum on that hose when running.

 

Easy to tell if you do, crank it, get to normal op temp, idle and look to see if it’s in or out.

 

Yes, always. With the brand new IAC, I was between 1500-2000, for well over a week after reconnecting my battery.

And yeah, one of the times after tightening my throttle cables they were a bit too tight. Great throttle response...but also high idle. My truck now idles around 1,000, that's after multiple times taking the throttle body off (I can have it off in under 5 minutes at this point), always disconnecting the battery first.