Throttle Body Design Flaw Leads to Sticky Throttle/High Idle - LotusTalk - The Lotus Cars Community
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post #1 of 35 (permalink) Old 02-26-2011, 12:13 PM Thread Starter
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Throttle Body Design Flaw Leads to Sticky Throttle/High Idle

The Toyota throttle body on the 2005 Elise (cable linkage, not the throttle by wire of later years), has a design flaw which can lead to the throttle not fully closing when released. I have had the problem on two throttle bodies, and isolated the problem as the being same cause in both cases. The first time the throttle body was replaced under warranty (although I diagnosed the root cause before bringing it to the dealer). The second time I made a positioning bracket to fix the problem (it was out of warranty, and I didn’t want to spend $900 or more on a new throttle body).

The problem is that the butterfly valve shaft lateral position (and hence the position of the flap inside the throttle body bore) is set by the flap touching the walls of the bore. When the flap is open, only the very small portion of the flap next to the shaft is touching the bore, and thus is all that is positioning the shaft laterally. If there was no lateral pressure on the shaft, this wouldn’t be a problem. However, the torsion springs that force the throttle to close put a slight outward (towards the cable quartile) force on the shaft. (See “spring” picture.) It wasn’t the design intent for the springs to do this, but the nature of how they are wound causes them to push out just a tiny bit (at least the ones on the two throttle bodies I have had).

Eventually, this pressure causes the flap’s inner portion (near the shaft) on the quartile side to wear, which allows the shaft to shift towards the quartile when the valve is open. When the valve closes, the now out-of-round flap outer portions (away from the shaft) rub against the bore as it is closing. As the wear becomes worse, the rubbing friction (counter-torque to the springs) becomes significant enough to make it stick open unless the throttle is snapped closed. (“Wear pattern” picture shows the flap wear on one side. The picture makes it look a little larger than it is due to the light blooming in the camera.)

A proper design would have used a retaining ring, or a shoulder on the shaft fitting into a groove, or other method, to set the lateral position of the shaft, and not rely on the flap itself to be the positioner. A good design would at least have made sure that neither the torsion spring nor the throttle cable (or anything else) could cause even a slight lateral force on the shaft.

My fix to this problem was to fashion a rigid steel right angle bracket with a set screw that positions the shaft (see bracket pictures). The bracket attaches to the full throttle stop and spring posts on the throttle body using a screw between the posts to clamp it to the throttle body. The right angle bracket reaches out and over the quartile, allowing a set screw to be centered on the end of the shaft. The bracket (after suitable cutting it to shape) does not interfere with the rotation of the quartile at all. After manually positioning the shaft where it should be (hold the quartile and push in towards the body while rotating open and closed), the set screw is simply lightly hand tight (snug – no play), enough to position the shaft, but puts no significant force on the shaft (if you put too much force on the shaft, you will cause stickiness and wear on the other side of the flap). The set screw is clamped in place with two nuts, one on each side of the bracket. (I could have tried to make threads in the bracket so that I would need only a single nut, but I wasn’t sure that I could drill the set screw hole accurately enough to center it, and was concerned I might have to oversize the hole a bit.)

After using this for 3 weeks, it is still working great. The throttle operates like it did when new. I even passed my California smog test with it last Friday (I wouldn’t have passed if it was sticking).

I did have to readjust the set screw after one week because I didn’t tighten it enough. Originally, I had backed off slightly from the screw touching the shaft when the shaft was properly positioned, but that turned out to be a mistake. I reset it, making sure it was actually touching the shaft, and wiggled the screw and the nut on the shaft side to make sure it was square to the bracket and there was no play in it, before clamping down the outer nut. I observed the screw closely to make sure that it didn’t turn as I was clamping the nuts torwards each other.

Material: (I bought all this at my local Home Depot – cost about $8)
  • Right angle bracket: Zinc plated steel, 1/8 inch thick, 5 inch per side (got it from Home Depot). I cut it down and shaped it using a Dremel tool (using about 6 cutoff wheels ). I used a thick bracket because I wanted it to be very rigid. (I would have preferred aluminum, but couldn’t find anything big and thick enough.)
  • Set screw: M4 (4mm diameter), 0.7mm thread spacing, 20mm long
  • Set screw Nuts: two M4x0.7
  • Clamp screw (clamps bracket to posts): M4x 0.7 x 20mm
  • Clamp screw nut: M4x0.7 (in hindsight, I should have used a lock nut - Home Depot had them)
  • Clamp plate on opposite size of posts from bracket: large thick fender washer, shaped with Dremel tool, and holes drilled for the clamp screw and for the spring ends.
  • Small flat and lock washers for clamp screw.
In retrospect, I think I would want some extra clamping of the bracket to the posts (the one screw makes me nervous), but it seems to be staying secure (I check periodically). Also, if the bracket starts to rust, I will need to paint it with a rust-protection paint.
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post #2 of 35 (permalink) Old 11-22-2011, 05:44 PM
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Is it just the butterfly flap that wears? Could this be fixed by replacing the flap?

Howard
2005 Elise AP LSS hardtop
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post #3 of 35 (permalink) Old 11-25-2011, 01:02 AM Thread Starter
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The throttle body bore showed some wear marks, but it appeared to be the flap that really wore down. My original thought was to replace the flap, but I couldn't remove the screws that clamp it to the shaft without stripping the heads. So, I came up with this approach instead.

I now have almost 10 months and about 10,000 miles on this repair, and it is still working perfectly.
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post #4 of 35 (permalink) Old 12-17-2011, 10:13 AM
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I have found some information indicting the throttle body is integrated with the cooling system. Is this correct and do I have to drain coolant before removing it?

Howard
2005 Elise AP LSS hardtop

Last edited by hroundy; 12-17-2011 at 04:37 PM.
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post #5 of 35 (permalink) Old 12-17-2011, 02:47 PM
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There are two coolants lines to the TB. Some people remove them completely and just bypass the TB (one less place to leak), but if you're in cold weather, it may be best to leave it there. Not sure, your call.

But no, you can get hose clamps/vise clams and simple choke off the tubes to/from the TB pretty easily and just disconnect the tubes (standard pinch clamps). It will spill some coolant from what is in the TB, but it won't require an entire replacement.

If brute force doesn't work, you're not using enough.
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post #6 of 35 (permalink) Old 12-17-2011, 04:50 PM
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Thanks loki007. Given my climate I will probably not do a bypass. I am thinking of redoing the bushing or adding a spacer on the side of the shaft that is creating problem. If I can do what I want, it will hold the flap away from the body having a similar effect ChrisH's mod. However, it will require the removal of the flap that ChrisH said he had trouble with.

Howard
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post #7 of 35 (permalink) Old 12-17-2011, 04:52 PM
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Interesting development! The picture showing light through the worn areas is very telling.
How many miles on your throttle body to show this kind of wear?
Does anyone know if this is prevalent over newer model years or did Toyota update the TB at some point?
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post #8 of 35 (permalink) Old 12-18-2011, 09:46 AM Thread Starter
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Quote:
Originally Posted by ///MD View Post
Interesting development! The picture showing light through the worn areas is very telling.
How many miles on your throttle body to show this kind of wear?
Does anyone know if this is prevalent over newer model years or did Toyota update the TB at some point?
It isn't so much miles, but what kind of driving you do (how much movement of the throttle). It occurred on mine twice, each time after about 35,000 miles of mixed highway and twisty mountain roads.

Note that this seems to be fairly rare, and could be due to some of the throttle return springs being faulty and putting too much outward lateral force on the shaft. But, I still contend it is a poor way to design it.
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post #9 of 35 (permalink) Old 07-02-2012, 10:09 AM
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FWIW, after weeks of putting up with a sticky TB, I made myself the Chrishbracket yesterday - worked like a charm, and only took me an hour or so. Great fix!

'05 SB Elise, TP, ST2, dual HID, driving lights, 4tress, schroth 4pt asm, TP rail, SYS, CRD, microMirror, HNTpad, V1
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post #10 of 35 (permalink) Old 07-15-2012, 05:24 PM Thread Starter
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It is nice to see my fix has helped out someone else.

I now have almost 18 months and about 18,000 miles with this fix, and it still works perfectly.
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post #11 of 35 (permalink) Old 03-23-2013, 12:42 PM
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Chris, it looks like you may have another happy customer - I just noticed my light was on and the idle was high. Nudging the throttle (either by hand at the throttle body or using the pedal) un-sticks it, by my check engine light is still on. I noticed the codes include "Idle higher than expected", but how long do these lights persist? Does it have to be manually cleared? I went by an O'Reilly's and they tried to scan it, but it said that it couldn't connect. Thoughts?
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post #12 of 35 (permalink) Old 03-23-2013, 04:00 PM Thread Starter
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Did you do the fix, or are you still letting the throttle snap close to get the idle to normal? The idle needs to be consistently normal for the check engine light to go out.

I would think the check engine light would go out after a 100 miles or so, and 4 to 8 drive cycles (with ~5 minutes between cycles).

I don't know why O'Reilly's scanner couldn't connect. With my OBD-II cable I use with my laptop, I have to connect the cable to the car and the laptop, get the program up and running, turn on the ignition, then have the computer connect. If I disconnect, I have to turn the ignition off, then on, and have the program reconnect.

You really should get your own OBD-II interface for your laptop, tablet, or smart phone. You can get ones that work fine for $25 or less at Amazon. It doesn't make any sense to not have one. I have both of the following ones:

USB cable version (software that came with it was fine)



Bluetooth (download the Torque application for Android Tablets or phones)


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post #13 of 35 (permalink) Old 03-24-2013, 07:14 AM
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I haven't done the fix yet, but I can just toe the throttle and that fixes it. Does disconnecting the battery for a few minutes reset it?

I just got the car recently, and the previous owner(s) was an idiot. I just replaced the radio wiring and the rear speakers don't work, so I have some electrical issues to hunt down. I wouldn't be surprised if something is off with the OBD comms. I already started looking at scanners, but I've heard the bluetooth ones aren't the best, but it is worth a shot for $25.
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post #14 of 35 (permalink) Old 03-24-2013, 11:38 PM Thread Starter
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I have heard that disconnecting the battery for a few minutes (suggest 10) will clear the engine light, but I have never done it myself.
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post #15 of 35 (permalink) Old 06-18-2013, 04:51 AM
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Having a friend with a scanner tool will also clear the light

I decided to take the throttle out and clean everything, and that's when I found that one wire to the idle speed control valve was severed. Rebuilt the connector, and now it idles! The sticky throttle is still evident but only by 100rpm or so - not enough to reset the light. Given the number of "band-aid" fixes on this car already, I'm trying to do everything by the book, but that bracket may be inevitable.


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post #16 of 35 (permalink) Old 10-25-2013, 01:02 PM
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I just wanted to add another Thanks to ChrisH for figuring out this problem! I have a pontiac vibe GT (same engine), and couldn't find anyone else with this problem (the GT was fairly rare). I had to make the bracket a little differently since my throttle cable goes the opposite way, but it solves the problem perfectly!
Thanks again!
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post #17 of 35 (permalink) Old 01-29-2015, 07:00 AM
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An interesting, if somewhat scarey, thread.

Do you know if the drive-by-wire TB have the same issue?

2009 Saffron Elise
1986 Toyota Tercel - RIP Oct 20/2012
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post #18 of 35 (permalink) Old 01-29-2015, 07:09 AM
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Quote:
Originally Posted by David Craig View Post
An interesting, if somewhat scarey, thread.



Do you know if the drive-by-wire TB have the same issue?

They don't since the electric motor an force it closed. It is just slightly open, so it doesn't lead to a runaway car scenario from what I can tell. Granted, it could still drive itself around at parking lot speeds


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post #19 of 35 (permalink) Old 01-29-2015, 10:24 AM
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You've just opened my eyes to the problem I've been having on my Corolla XRS.
It has about 130 k on it and I will probably do your fix, if and when the weather fixes itself.
Thanks. Sam

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post #20 of 35 (permalink) Old 04-28-2015, 01:29 AM
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Sorry for raising this old topic.

Looks like a decent solution to the sticking throttle body problem. I have the same issue on mine so going to give it a good clean, and if that doesn't work, will probably do this mod, just wondered how you got the measurements for the holes to drill. Was it just guesswork or is one of the hole oversized in order to get the retaining screw in the right place please?

Also, is it possible to get the TB off without getting at it through the wheelarch please?
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