FaceUT

Having purchased a Throttle Position Sensor for my 92 LS400, I am trying to determine if I can install and properly calibrate with my multi-tester. I have read everything I can find on the forums about this, but I am still unsure of where to obtain my readings. It seems everything refers to using a scan tool, but makes reference to being able to use a multi-meter to adjust to the proper settings.

Do I need to test the TPS percentage's at the "Diagnostic" outlet? If so, which ones do I plug into?






Thanks! Any input would be appreciated.

pscmj

Here’s the procedure I followed on my ’94. It is probably the same for your ‘92. The critical detail of the adjustment is setting the position of the switch point from continuity to open resistance between TPS terminals E2 and IDL. This procedure uses a simple multi-meter connected between terminals E2 and IDL on the TPS (the TPS is essentially a variable resistor – potentiometer – with no active devices). These terminals are the “bottom” two terminals of the four TPS terminals when installed in the vehicle. To access the terminals, ensure the ignitions is ‘OFF” and remove the plug connected to the TPS. Note: it is difficult to see and connect the multi-meter leads to these terminals. I connected a pair of insulated alligator clips to E2 and IDL (make sure not to short the leads together as this will affect adjustment) and then connected the meter leads to these clips (of course alligator clip meter leads would even be better). Once the meter is connected, adjustment can proceed with the following steps.

1. Loosen the two TPS mounting screws … they should be loose enough to allow turning of the TPS, yet tight enough to somewhat hold the TPS in place.
2. Slowly adjust the TPS by turning the TPS body clockwise or counterclockwise until the multi-meter reading is less than 2 Ohms.
3. Insert a thickness gauge (0.4mm/0.0157in) between the throttle stop screw and lever.
4. “Very” slowly turn the TPS clockwise until the meter just switches from a less than 2 Ohm reading to infinity (open circuit). This is the critical setpoint of the adjustment.
5. Repeat steps 2-4 until there is less than 2 Ohms between E2 and IDL with no gauge, and open circuit (infinity) with the gauge.
6. Tighten the TPS mounting screws AND re-verify the setpoint as tightening of the screws can alter the setpoint. If the setpoint has changed, repeat steps 1-5.
7. Reconnect the vehicle plug that normally connects to the TPS.

These are the basic steps for TPS adjustment. Not too bad once the meter leads are connected. I should add that the car will perform differently (more responsive/less responsive to throttle input during driving) with varying setpoints. The ’92 setpoint may be different, but this procedure should get it in the ballpark. Experimentation in increments of 0.2mm either clockwise or counterclockwise will yield optimal results for your driving preferences. Good luck …

pscmj

One minor change to the procedure outlined above. I took another look at my "feeler" or thickness gauge, and the increments of change should be about 0.05mm, NOT 0.2mm as I had stated. Suggested setpoints (with 0.4mm / 0.016in as nominal) are as follows:

Inches / MM
0.018 / 0.457
0.016 / 0.406
0.014 / 0.356
0.012 / 0.305

dunn378

when u say infinity (open circuit) that means the meter is reading 0 right?

FaceUT

This was exactly the information I was looking for! I installed a new TPS this afternoon and it appears to have fixed the problem I was having with the idle suddenly dropping 200 rpms when easing off at 1800 rpms. You were absolutely correct on how difficult it is to obtain readings off the bottom two terminals of the TPS. Lacking the alligator clips you mentioned, I chose to remove the air intake to allow for a little more room. My God, what a sensitive calibration! If I had it to do over, I would have made a run to a parts store for some clips.

I chose to use the .016 feeler gauge. I can't say I have a good feel for what changes I should expect in performance by varying the gauge used to make the calibration. I would assume it would alter idle speed.
What other changes would occur?

When finished my 92 LS idled at 650 rpms when warm in park. 600 rpms when in drive. And around 1100 when cold. She seems very smooth with zero shuttering noted. And I could not make her hesitate at 1800 rpms!

Thanks again! The local garage said it would run me at least $45 to install and calibrate the TPS. Nothing like the satisfaction of DIY!

FACEUT
NC

dunn378

how much did u pay for your tps FaceUT??

FaceUT

About $73 + shipping from Irontoad.com. Also ordered a set of plugwires and an oil filter/gasket for drain plug while I was at it. Total $186

pscmj

Glad things worked out. Alligator clips do make a BIG difference. Also, with regard to meter readings, a "0" reading indicates 0 Ohms (a very low resistance between the points of measurement - a short circuit). If the meter leads are shorted (connected) together, the displayed value should be 0 Ohms. An open circuit is a very high or infinite resistance between the points of measurement. For most meters (digital and analog), the displayed value of an open circuit (infinite resistance) will not change when the meter leads are connected between the points of measurement versus when the leads are not connected at all. Hope this helps.

One final note. TPS adjustment in the ranges referenced will NOT affect idle speed. The only time I noticed idle changes is when I had adjusted the TPS all the way clockwise (I think it was clockwise). Idle speed on the LS400 is controlled by the ECU pretty much regardless of the TPS setting (within reason that is).

FaceUT

If the TPS setting will not effect idle, can you help me to understand what changes a slight under or over adjustment will make? I also wondered if I should reset the ECU following the installation. Although at this point she seems to be running great!

Thanks for all your help!


FaceUT

pscmj

As you probably already know, TPS stands for throttle position sensor. As implied, this sensor provides electronic feedback (varying voltage levels either greater or smaller depending on the accelerator position) to the computer (ECU). The ECU in turn increases/decreases fuel flow depending on the feedback (ie throttle position) received/sensed (please explore the web for more detail). Through experimentation I performed with my ‘94, (and I’m going from memory here so I may have the directions reversed), the more clockwise the TPS is adjusted the more responsive (ECU senses accelerator changes quicker – more feedback) the engine will be, whereas the more counterclockwise the TPS is adjusted, the less responsive (ECU senses accelerator changes more slowly – less feedback) the engine will be. The response changes are slight, but noticeable. I should also add that the referenced set points will not affect idle (as stated above) or wide open throttle (WOT) performance.

I would always drive for at least a day (I drive about 50 miles/day) between TPS adjustments to make sure the ECU was reacting consistently to the new setting (although I never noticed any ECU response changes during the day, and I always felt the effects of the new adjustment positions immediately). Also, I didn’t reset the ECU after adjustments – never seemed to be an issue.

Again, I’m very glad to hear the success stories. Hope this crude explanation helps.

1994 LS400

Hey ~
I am wanting to change my TPS sensor in my 1994 LS400, But I am having trouble from the very start. I am unable to remove the screws that hold in the TPS. I have a multi-tester , and will get some alligator clips. but I need to know what kinda screw driver to use, I have started to strip one screw and I cannot even get to the ohter one. I guess I need to take out the airt intake ? I want to do this but Have never worked On my LS before (Except change the Power Steering fluid ) ANY help would be awesome.
Paul

pscmj

Paul,

Just a friendly word of caution - unless you are having problems, I would NOT change the TPS or alter your current TPS adjustment (I'm concerned that hesitations or other performance problems may actually be induced by altering the original factory adjustment). Anyway, if you decide to continue, you DO need to remove one of the hoses that blocks front access to the screws (I forget the exact layout, but it's fairly simple to get the hose out of the way - only takes about 30 seconds and can be done with a pair of pliers on the hose clamps). Once you do this, a #2 Philips screw driver should do the trick (make sure the tip is in good shape and not rounded off). I actually went to the hardware store and got some allen-head replacement bolts so I wouldn't have to keep removing the hose with each new adjustment - Lvangundy posted a thread on the exact part he used. I just took my old screws and matched them to the allen-head bolts from the hardware store. MAKE SURE THE THREADS MATCH EXACTLY. If you're unsure, find some nuts at the hardware store that are the same thread size as the original TPS screws, and make sure the new bolts screw into these same nuts. After that, the above adjustment procedure should go pretty smoothly.

Good luck ...

1994 LS400

Hey !
Well I did it ! , I changed it I bought the new/updated TPS sensor for $190 !!! from Lexus ( The Mothership Stealer) and installed it , the factory setting was ALL the way over, making it slower , so for a little fun I tweeked it just a little and WOW she is SO responsive,quick and so smooth ! However , Me wanting my car all factory, I will be moving the sensor back to factory setting , I had my fun, Thanks for you advice/help !!!


Paul

pscmj

Paul,

Isn't it absolutely criminal how Lexus marks up its parts!!! Anyway, sounds like you got the new one installed, and everything seems to be working fine. Glad it worked out so well.

Enjoy ...

1994 LS400

pscmj~
Well I have come to a conclusion that I want the car to be 100% factory , and I have a multi-tester, I have all these diffrent settings for Ohms, I chose X1 (Is that correct). So what reading am I looking for on the Gague... 2 and then infinity, also what is a feeler gague ?
Thanks !
Paul