Squeeto

The throttle position sensor modification:

This is the second modification made to fix transmissin hunt and thump issues.
(See the first, valve body fix also)

<img src="http://pictureposter.audiworld.com/125817/tps_mod.jpg">

The TPS is a variable resistor and a switch that is contacted when the throttle is at idle. The resistance increases (pin3 to 2) as throttle is depressed. We move the point at which the idle switch is contacted so that more resistance is present at idle. The throttle body throttle valve hasn't moved but we are telling the car that it is open more than it actually is.


VagCom (VWTool) measurements:
Engine
Data Blocks
Block #4
...............................to spec........my original......full throttle to spec.....my full throttle
Throttle angle (actual)....5 to 10........8.3..............80 to 98..................87.5
Throttle angle (learned)...0...............................79.2
Operating Cond..............Idle...........Idle............. Full TP...................Full TP

"Part TP" should show for slight pedal movement from idle.
The VagCom software will also show you any unwanted glitches on the graph as the angle changes.

Note that the procedure for resetting the TPS is:
-ignition on and car not running
-slowly push gas pedal to floor over 15-20sec, hold for 5-10, release slowly over 15-20sec
-turn car off for 2-3min

It takes a few miles until the car settles down and learns how to use this "new" TPS.

Extra to note:
-originally, in the "clicked" position, pin3 to 2 measured 946 ohms
-VagCom readings after the mod are-
idle 10.7 full 90.3
learned 2.4 82

You may need less bend on the tab (or more?) than I did. It is best to see what works best for your car. If enough people try this, more results will bring about a standardized value.


TPS re and re: (mostly from notes PaulW made a while back in the forum)
1. Remove engine covers

2. Unbolt 13mm nut that holds cruise control vacuum positioner, remove the vacuum line and remove positioner from bracket. This will prevent you from breaking the yellow plastic washer that holds the linkage in place.

3. Remove air inlet rubber tubing to throttle body (5 inch oblong). Remove in 2 pieces.

4. Unplug two electrical connectors, one on bottom left (looking at it from passenger side fender) and one on the top.

5. From the passenger side fender and using a 6mm hex socket head on a 3/8" drive extension, remove 5 hex head bolts holding throttle body (which houses the TPS). Remove the hose at the top; it has a one time crimp but it still just pulls off.

6. Remove TPS electrical connector once it's loose, it's on the back side.

7. Pull out the throttle body.

8. Unscrew two phillips head screws holding the TPS to the body, best to have another set of hands to hold it so you don't strip the screws.

9. Install new sensor, and adjust it so it clicks just as the throttle opens up. Play with it a little bit, it's easy. This is the idle micro switch.

10. Install is reverse of removal.

PaulW

I found after a week or so, it started hunting again, but just at different speed ranges.

Squeeto

I drive a certain route quite often and I found that at one hill I always hunted. After my first attempt (mod), the hunt went away for that hill but started hunting for another section of the same route.
The conditions that caused hunting had "shifted".

We need to find the sweet spot where all conditions of this oscillation are never met.
This is still just a patch though. The true fix would be new software.

The way I have it is fairly good now but it is not where it will be after I have tested the valve body mod.

I think that I modded this about a year ago. I am sorry that I didn't post this sooner but it (with the valve body) is still a work in progress.

PaulW

It's something worn in the valve body, this just allows it to control it slightly different.

PaulW

Added to FAQ

TOMAS7

If so, then isn't it a TCU issue? Am I way off here?
Doesn't the tranny on the D2 have a learning capability?
Couldn't it be taught not to hunt or to stay in gear whatever that gear may be?

Squeeto

Are our TCUs flashable?
I posted a TSB a few days ago which shows an upgrade for the TCU (and VB) but I am not sure if this is accomplished with a flash or a new TCU.

JimTheBarber

Isn't it the case that the guy who stuck the 4.2L V8 in a Lotus chassis wrote his own ECU?

CalG

The control programs are sophisticated.
We really only are interested in the TCC control portion. Adding a bit of "time"(two seconds?) to most controlled slip commands might take care of the "hunt". The "thump" may benefit as well. I'm not sure.

Question: Isn't the TPS mod just to address the "thump"? I can't see any connection between TPS base signal and "hunting".

Now, if I can just "find" that old TPS.....;-)

Regards

CalG

Squeeto

I think I read a while back that BMW did just that with a one second wait added to the control for their 5HP24.

I also remember a forum member with some experience in this offer his services. I'll see if I can find the post.