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TPS calibration on 3800's


Low Mount 3800 ALT!

Low mounts in stock today. Newest design has tension belt assembly, cleaned, and blasted. 

Throttle Position Sensor Optimization


What the Throttle Position Sensor is: The throttle position sensor (TPS) on the throttle body is a little known yet very key sensor. The TPS tells the computer what position the throttle blade is at; from this, the computer can see how to control timing/fuel as well as shift points for the transmission. The TPS is a resistor sensor, it will alter a 5 volt input based on its position and send that output voltage to the PCM, which will inturn recognize the voltage as a percentage of throttle opening. 

The reason for doing this mod: Factory settings on the throttle position sensor aren't made to very exacting tolerances, our TPS sensors appear to give acceptable voltages when bolted onto the throttle body to allow for proper idle and to see WOT. Normally observed voltages are .4v at idle and 4.1 at WOT. This leaves some room to improve by optimizing the idle and WOT voltages, which changes the operating range of the sensor. 

What this mod will do: Imagine if you will a range between the two values, idle and WOT, with part throttle inbetween. This is the operating range of the sensor. Along this range, you have points at which certain upshifts occur, or downshifts, or power enrichment fueling, and finally a voltage that you hope the PCM recognizes as WOT. 

What we are essentially doing with this modification is moving this sensor's operating range up and down by adjusting it but remember that the points stay the same, only the range moves. By doing this, we can control how soon these points are reached. 


As an addition to this mod, we are also adjusting the idle set position a little further open. While the PCM will learn the idle voltage and this will NOT raise idle speed, it will give you more throttle response as you initially step on the gas. This part of the mod is optional but if you have a stock throttle body high consider giving this a try! 

The benefits of this mod: 
Increased throttle response with optional idle adjustments 
Better part throttle fueling - Power Enrichment reached sooner, aids part throttle KR 
Ensure the PCM observes 100% throttle input at WOT 
Slightly more responsive downshifts at part throttle 

Tools needed to modify the TPS: 
Torx-T20 "safety" bit, T15 bit or small philips, and driver 
Drill and various drill bit sizes 
8mm socket or wrench 
Two M4 washers, may also be a good time to get two allen head M4x12mm bolts to replace the pesky Torx ones with 
Throttle body gasket (if removing the throttle body from the <A TITLE="Click for more information about car" STYLE="text-decoration: none; border-bottom: medium solid green;" HREF="|1||||cars|AA1VDw">car</A>) 
Autotap or multimeter 

How to adjust: 
To assist in the adjustments, you may find it easiest to take the throttle body off the car, however these can be done with the throttle body on the car as well. If you take the throttle body off, it is recommended you get a new gasket and you must hook up the TPS sensor connector to read its voltage. If you leave it on the car, you can also remove the thermostat housing to gain better access to the TPS sensor. 

Our sensors come from the factory non-adjustable, likely to make factory assembley easier. So we must make the sensor adjustable before anything else. To do this, we must remove the sensor from the throttle body. 
1) You'll need your T20 bit to take the sensor off, and it must be a safety bit with the hole in the center. This is where taking the throttle body off the car or removing the thermostat housing aids in the ease of performing this mod. Remove the two screws retaining the sensor, visually note its position and finally remove. 


2) With the sensor off the car, the two mounting holes on the sensor itself must be enlarged to allow room to move it back and forth on the screws. Drill out the metal insert in it first using a drillbit only as large as the metal insert, then drill out the holes again to 1/4". 



3) Replace the sensor on the throttle body, taking care that the sensor tab on the backside goes on the underside of the tab on the throttle body, you will have to hold the sensor slightly clockwise as you install it. Install the screws loose to allow sensor rotation 

4) Now hook up an autotap or equivalent scan tool, or you may also use a voltmeter on the sensor wires by setting it to read up to 5 volts and tapping the ground into the black wire and the power to the center wire on the TPS connector. 

5) With the ignition on but engine off, measure the voltage of the TPS while the holding the throttle linkage at full throttle. You will want to rotate the sensor on the screws until you see 4.3-4.35, then tighten the screws on the sensor to secure it. Recheck the voltage to assure it hasn't changed. *Note: Autotap will only allow you to see one decimal place on the voltage. Move the sensor until you see the voltage just change from 4.2 to 4.3 and stop there, assure you see 4.3 after tightening the sensor. 

Now lets adjust the idle voltage, which in doing so adjusts the throttle body blade position at rest. This part is optional but highly recommended to stock throttle body users. If you do not wish to perform this section, simply ensure idle voltage is under .75 and if not, adjust the TPS sensor down until it is. 

There will be a screw below the cable linkage on the right hand side of the throttle body, it will also have a nut on it; this is the idle stop screw, it is used to determine the position of the throttle body blade at rest. 


1) Use the 8mm wrench to loosen the nut first. The screw itself can now be turned, if you have strong fingers you should be able to turn it by hand however if its tight then the end of the screw will have either a philips or T15 Torx head. *Note* Holding the linkage open by hand while you turn the screw will aid either way you do it, just be sure to release the linkage to its rest position before noting the voltage at idle. 

2) *NEW July 22 2004* 
*Scantool method (preferred)* 
This method is the best no-guess-work method. Using an Autotap, Car-Code or similar scanner, read the Idle Air Control count or position (called IACC in CarCode's enhanced menu) along with the TPS voltage. Start the car and bring it up to a warm idle in park. Now using the IAC count reading, adjust the idle stop screw until you see a consistent reading of 10. You will have to let the car idle for a few minutes to ensure that the IAC readings aren't still adjusting and changing. If they are a constant 10, ensure the TPS voltage is under .75. If its over .75, you must bring it back down so that it is. I recommend setting the WOT voltage lower in such cases, as its usually 4.4x but can be brought down to 4.35 without adverse effects. 

*Voltmeter method* 
This is for users with access to a Voltmeter only. With the linkage at rest and the ignition on but engine off, adjust the screw until you see a value of .70-.71volts at idle. If you feel the idle speed is climbing with the adjustments you're making before reaching this voltage and not coming back down, adjust as high as you can go maintaining the desired stock idle speed. This is not uncommon on ZZP ported throttle bodies where the seal around the throttle plate isn't as good as stock, and a lower idle voltage is needed. *Note*Exceeding .75volts at idle will result in a high idle speed which the PCM may not full correct itself for. Anything higher than .75 at idle is not recommended. 

3) Once you're happy with the voltage, tighten the nut with the 8mm wrench again and verify the idle voltage. 

At this point, reinstall anything that needs to be and you're done! 

Things to take note of: 
    It is highly recommended that you reset the computer for 15 minutes to allow the computer to relearn the new TPS values. To perform the "TPS learn proceedure" upon first startup, turn the key to on, wait 30 seconds, then turn the key off. Now start the vehicle and let the idle learn. 
    The engine may idle high for the first few startups, especially if the computer hasn't been reset. This is normal and it will learn the idle adjustments needed to reach factory desired idle speed.

    Exceeding .75 volts at idle will result in a high idle speed, which the PCM may not fully recalibrate itself for. Try to keep idle voltage below this number.

    The computer may want to see 4.2 volts or higher to command 100% throttle. Also, Zex nitrous kits require 4.25 volts at WOT to activate. Instead of buying a throttle position sensor enhancer for $100US, this is a very viable and inexpensive solution to this factory annoyance.

Disclaimer: While the author uses this modification on his own vehicle with success and would recommend it to others, he cannot be held responsible for any mishaps that may occur on other vehicles the result of following this tutorial. You perform this modification at your own risk.


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