View Full Version : Throttle position sensor issue or something else??

05-07-2012, 09:11 PM
So the wire clip to my TPS basically fell apart on my st165 wiring harness, so I found another one on an old celica, wired it up and thought all was well. My original wires are pretty worn looking, as such that they all look darn near the same color and instead of soldering in one wire at a time, I cut all 4 at once and did my best to put them back where they go, according to the old clip but since putting it all back together it stalls a few times before it will start and idle when I start it for the first time of the day, no matter what the temp outside is and yesterday the car was running rougher and bucked more savagely than ever before when I was driving it cold. So to ask a question, does anyone know how I could test each individual wire running into the TPS, as far as with a volt meter and verify that wire one is running into terminal one, etc, etc? I know that I have 2 of the four correct but the other two wires both look the same color brown and I'm wondering if maybe I have them crossed? help:wondering:

05-07-2012, 10:02 PM
Use the BGB to get wire pinouts on the TPS, and then get the pinouts at the ECU, use the pinouts to use a DMM to test ohms between the sources. Thats how Id do it.

05-08-2012, 12:00 AM
That's interesting because that is what I thought too but according to the BGB schematic the only wire running into the ECU from the 4 wires that go into the TPS is a pink one. I'm not very experienced at reading wiring schematics but it looks like the other wires run through other systems. That makes this very confusing for someone with my lack of electrical knowledge.

05-08-2012, 12:15 AM
All 4 TPS wires run to the ECU.

From the bottom wire to the top

1) E2 - ground wire
2) IDL - sends the signal to the ECU that throttle is closed
3) VTA - sends the throttle angle signal to ECU
4) VC - is the 5v power wire coming from the ecu to the TPS

05-08-2012, 12:44 AM
OHHHHH, with your explanations and the schematic in front of me, I'm beginning to feel like a little less of a dummy. So, now to test which wire goes where, what do I do? I apologize but I really need a break down. Do I disconnect both harness, touch one end of the wire in the engine bay, then try to find the other end inside the floor board @ the ECU? Will the ohms be different per wire? Anything else I should know? I am a total electrical dumb ass. Thanks you guys, I am VERY grateful for the help!

05-08-2012, 04:10 AM
You can test the voltage from each wire at the harness plugged into the ECU. I'm sure you have the replacement plug for the TPS wired up wrong. Unplug the TPS plug and turn the ignition switch on. Use the diagram below to identify the location of the wires on the TPS plug. Using a multimeter I want you to touch the leads to E2 and VC on the TPS plug. You should have 4.5 - 5.5 volts(if you get 0v skip to #1 below this paragraph.) Now, to make sure you have the right wires connected to each other, do this. Touch one lead to VC and the other to the negative post on the battery. If you still get 4.5 - 5.5v then you know that E2 and VC are spliced to the right wire. That means that IDL and VTA are not spliced into the right wires. So cut those two wires, swap them around, and you should be good. To double check you can plug the harness back onto the TPS and check the voltage readings by back probing the harness at the ecu. Just follow the instructions below.

1. If you got a reading of 0v from e2 and VC then you have a wire spliced in the wrong spot. To find the 5v power wire touch one lead to the negative post on the battery and the other lead to each wire in the TPS plug until you find the 5v power wire. move that wire to the VC location on the TPS plug as per the diagram below. Then touch the multimeter leads to E2 and VC on the TPS plug and see if you now have 5v. If you don't then that means the ground wire labeled E2 on the TPS plug is in the wrong spot. So touch a lead to VC and the other to each of the other three remaining wires on the TPS until you get a 5v reading. When you get the 5v reading then you know you found the ground wire and it needs to be relocated to the right spot on the diagram.



05-08-2012, 07:13 AM
Wow man, thanks for the effort. I will try that tomorrow and let you know what I come up with. I have high hopes it will be a easy fix and even higher hopes that I'll cut and solder 1 wire at a time from here on out! duh.... Thanks again

05-08-2012, 07:49 AM
My little Bruce is teaching people how to diagnose electrical issues with a DMM. They grow up so fast!

05-08-2012, 02:45 PM
The student becomes the teacher.

05-09-2012, 05:53 PM
Ok, so the update.... Tested at the TPS plug and found that E2 was crossed with VTA, swapped them. Now I have the proper voltage between E2 and VC and I confirmed that at the ECU. So I started the car this morning and it still fought me so I ran some other tests and here is what I got at the TPS plug with ignition on and grounded to battery negative terminal: VC 5.02 volts, VTA 1.74 volts, IDL 10.37 volts, E2 .031 volts.... Next I checked the ECU: IDL-E2 was 10.29 volts @ full throttle (which according to specs, is too high), VTA-E2 was .578 volts @ no throttle (ok) and 3.82 volts @ full throttle (ok), VC-E2 was 4.99 volts (also ok). So then I check wire resistance at the ecu terminal as per instructions and IDL-E2 @ full throttle was infinity (ok) no throttle .420 ohms (ok ,I think), VTA-E2 @ full throttle read 8 ohms which seems wrong and at no throttle read 6.57 ohms which is also wrong, so I am totally lost. This is giving me a headache. Is there something I'm doing wrong? Could I have messed up my computer (ECU) having had the wires crossed and driving for a few days? Ugh, I need some excedrine....

05-09-2012, 08:44 PM
I'll respond in more detail shortly. I have a couple of tests I want you to do You may have fried the TPS by grounding to the VTA on the sensor. If that's the case I have a brand new OEM Denso TPS laying around I could sell.

05-09-2012, 11:24 PM
VC 5.02 volts, VTA 1.74 volts, IDL 10.37 volts, E2 .031 volts....

When you checked these reading was it with the TPS harness plugged into or off of the TPS? Yes, the voltage on IDL is way out of spec. Also, there should never be voltage on the E2 ground wire. This is why I suspect the TPS was grounded out when you had the wires crossed. The 5v signal from VC is input from the ECU into the TPS. That signal feeds the potentiometer and in turn is sent back to the ECU as a control signal through IDL and VTA.

Next I checked the ECU: IDL-E2 was 10.29 volts @ full throttle (which according to specs, is too high), VTA-E2 was .578 volts @ no throttle (ok) and 3.82 volts @ full throttle (ok), VC-E2 was 4.99 volts (also ok). So then I check wire resistance at the ecu terminal as per instructions and IDL-E2 @ full throttle was infinity (ok) no throttle .420 ohms (ok ,I think), VTA-E2 @ full throttle read 8 ohms which seems wrong and at no throttle read 6.57 ohms which is also wrong, so I am totally lost. This is giving me a headache. Is there something I'm doing wrong? Could I have messed up my computer (ECU) having had the wires crossed and driving for a few days? Ugh, I need some excedrine....

All of that looks good except for IDL of course. If you have the wiring right then the TPS is likely the culprit.

I'm going to make a parts for sale thread that will have a New TPS if you are interested. It's a Toyota Denso sensor that is new in the box. I'll let it go for $45 shipped.

05-10-2012, 03:52 PM
Both sides. The IDL at the ECU with the TPS plugged in was the same as the IDL terminal unplugged from the TPS, which is why I was worried about the ECU itself. I'll check it again and I'll do the resistance test at the TPS terminals and get back to you. If I do need the TPS, I'll want to pick up yours, but as far as I can tell, it is wired up correctly as everything else reads within specs....

05-11-2012, 03:38 AM
So it looks like I may be buying your TPS. I ohm tested mine with the ignition off, with the plug unplugged at the TPS terminals with feeler gauges on the throttle stop screw and my readings are at 0 mm clearance 715 ohms between VTA-E2, @ .50mm clearance IDL-E2 read infinity and the same with the clearance of .70mm (which is within specs). With the throttle fully open, VTA-E2 read 4.28k ohms (within specs) and VC-E2 are 5.53k ohms (also within specs). What do these readings mean? Do I need a new TPS and is so how can I go about purchasing yours Hookecho? I really don't know how to do anything else on this site except use the forum. Please guide me, wise one! Thanks for the assistance

05-11-2012, 05:15 AM
Well, the only reading that is off is IDL/E2 at 50mm. It shouldn't read infinity. You may can adjust the TPS a bit to get it to ohm out right. The ohm readings the bgb gives are for adjusting the TPS. If you can't adjust it within spec then replace it. The voltage readings are what you should be concerned with the most. Getting 10v on IDL is concerning. So was getting a voltage reading on E2. Do me a favor and test those wires for voltage again. With the ignition on and using the neg post of the battery for ground. Unplug the TPS harness and probe the each wire again and tell me the results. You should only get a voltage reading on VC. If you get a voltage reading on any other wire then the problem is the ECU.

05-11-2012, 04:23 PM
There is voltage at every wire at the TPS plug: VC 5.05vdc, VTA 1.777vdc, IDL 10.58vdc and E2 .060vdc.... Bummer, so my next question is, I have the st185 JDM ecu from the motor I'm running. Can I use that without ripping out my wiring and changing all the sensors, like with some sort of plug n' play adapter or should I just pull my computer and have it repaired? I guess, put simply, what should I do next?? Hey man I really want you to know that your assistance has been a tremendous help. I'd be ass out without it. Thanks again!

05-11-2012, 04:34 PM
Do you have a 185 motor in you 165?

05-11-2012, 07:41 PM
yup but I used the st165 intake manifold, sensors, wiring loom and ECU

05-11-2012, 08:49 PM
You'll have to look at the pin out for each ecu and see what wires need to be relocated on the patch harness if you make your own. You may can buy the patch harness. There are others that are more familiar with the 165 than I am.

here are some of the pinouts for the 3sgte.



St165 pinouts


05-12-2012, 11:01 PM
Think it'd be better to do that or just get another st165 ECU? I don't want to pull the wiring loom. I guess I could chop both wiring harness up and at the plugs and switch whatever is needed, around. The st185 ECU provides more power right? It worries me though because of the fact that I am running the st165 throttle body with the cold start valve and I've read the st185 does not support that mechanism. What'd, y'all think??

05-13-2012, 12:34 AM
The st185 has a cold start injector. If you want to keep it simple then find a 165 ecu. You could make more power with the jdm ecu though. Open up your 165 ecu and see if you fried a resistor or something.

05-14-2012, 07:52 PM
Will do, I'll keep you updated. You know any one who repairs these things?

05-14-2012, 10:45 PM
Any place that works on CB radios or electronics can do it.

05-16-2012, 10:21 PM

05-22-2012, 10:02 AM
if i remember correctly, you run a resistance test on VTA - E2 with the throttle fully opened. now with the tps bolted up, adjust your tps to read within spec (3-10.3kohms). then you proceed to test the rest of the values within the chart above.

05-23-2012, 04:31 PM
So, I used the ECU out of my brother st165 and it still didn't start correctly, then I switched to his TPS and it started perfectly. Switched back to my ECU and it still won't start right so I think I cooked my TPS and the ECU.... AHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH HHHHHHHHHHHHHHHHHHHHHHHHHHHHH!!!!!!!!!!! Dialing in my project car, so far, has been very frustrating.

05-23-2012, 04:33 PM
Oh, also to anyone who cares, I've got a bunch of parts from my st185 jdm motor posted on ebay, i.e. intake manifold with sensors, wiring harness, ECU, turbo and a few other things as well. Just thought I'd put the word out.... Thanks again for all the help and advice!

05-23-2012, 06:11 PM
Yeah, when you wired up the TPS wrong and applied voltage to the E1 wire you fried everything. I know it has to suck. Don't feel bad though because we all make mistakes. At least you learned something.

05-23-2012, 07:25 PM
Except that it did it again with my brothers stuff. Then I remembered that I messed with the AFM the same time I worked on the TPS plug (another lesson learned, fix one thing at a time and test FIRST!!) So I went and snagged my brothers AFM, put all my original parts back in and I'm gonna start the process of elimination all over again. Gonna wait for the car to cool down then I'll post results. I'm gonna kick myself if that's the issue!

05-23-2012, 08:32 PM
So the car just started perfectly with my bros AFM. Does anyone know where I can get another AFM? :(

05-24-2012, 01:36 AM
Did you do this using your original ECU and TPS?

05-24-2012, 03:21 PM
ok, just tried it on the first start up of the day. No cold start so it isn't the AFM (and yes I used my TPS and ECU) so next I'm going to switch just the TPS. Process of elimination. I know the AFM is good now onto the next....

05-28-2012, 04:09 PM
Yup it's the ECU and the TPS. DOH!