Throttle Position Sensor (TPS) intermittent harsh gear changes and idle problems

[TubbyTwo]

Buggery Did they swap the torque convertor as well as the autobox itself?

 

The stalling problem still could be overfuelling, but if the TPS isn't working correctly then it might the the IDL switch line, the signal that tells the ECU that the throttle is shut and it should control the idle using the ICV. If that doesn't work, when the throttle is shut the engine struggles as the idle control valve is also shut and barely any air can get in. It's something you can check with a multimeter at the ECU, using a safety pin as a probe to go through the wiring insulation. You can also check the throttle signal like that, see what the ECU is actually getting.

 

I don't know what a dodgy TPS would do to the autobox control, but it probably won't help it.

 

yep complete swap including torque converter

 

Will go out and check the O2 signal shortly, bit of a multimeter noob so guessing its red pin to port in diag port and black to earth point?

 

is it worth trying to reset the TPS or just source a replacement and try that?

 

Im not great with electrics so the thought of having to fault find through looms etc is a bit daunting

[TubbyTwo]

By the way, do I test the o2 sensor with the engine off or running?

[Kristian_Wraae]

It is the TPS.

 

I had a broken TPS on mine at it stuck at the 3000 rpm line. Hard engagement when put into drive. And if the brake signal is not working then the torque converter wont disengage when comming to a stop.

[TubbyTwo]

sounds exactly like my symptoms, thanks

 

Well my drive home last night was fun and games, stalled and wouldn't restart stranded me for ages, then got it going In the p***ing rain, only to have the same happen again 2 miles down the road.

 

same happened again on the way to work so need to source a TPS urgently!

[Kristian_Wraae]

It could be a wiring problem.

 

Also check the wires from the brakelight to the ECU. It is pin 4 on the smaller single plug that goes to the ECU (On the US Supra it is green-white). Check it gets 12V when then brake pedal is depressed.

[TubbyTwo]

Will do thanks

[Ian C]

By the way, do I test the o2 sensor with the engine off or running?

 

Running, and warmed up

 

The TPS you can test with it off the car, as you check resistances. Checking the values it gives at the ECU needs the electrics on (ignition position 2) but the engine can be off. Id recommend doing these tests before randomly swapping components unless you have a TPS right there.

 

I might have a spare TPS, not sure, I won't be able to check for a couple of days though

[Ian C]

Will go out and check the O2 signal shortly, bit of a multimeter noob so guessing its red pin to port in diag port and black to earth point?

 

I wasn't great with electrics either until I had to in order to sort an earth problem on mine years ago. It's not that hard once you get past the scary amount of wires and stuff. Red pin to OX1, Black to earth or battery negative. If you get them the wrong way around it's not the end of the world, you'll just see a negative number instead of a positive one.

 

Testing the ECU wires is a bit more fiddly as you have to find the right one (TPS and IDL on the pinout diagram you'll find elsewhere on the site) and pierce the insulation with a pin and multimeter the pin. I used a safety pin with the multimeter probe poked through the coiled spring on the pin and taped in place.

 

TPS should show a changing voltage between 0-5v depending on throttle position. The IDL switch will either show 0 or 5v, or it'll be infinite resistance or no resistance to ground, depending on throttle position. I can't recall which

[TubbyTwo]

Right I have a day off tomorrow, so after an interview in the morning I will be cracking on with the car weather depending. I reset the TPS at the weekend, reset the ecu and went for a blast and it was great, then after an hour it went back to "hanging" at 3k rpm using loads of fuel and failing to idle properly.

 

Insurance is up next month and I think if I cant sort it, before then I cant see myself renewing it. I have already made a spreadsheet with breaking prices, that I really don't want to use but with work and my daughter I just don't have the time or energy and need a car that works properly. I'm afraid to press the throttle now encase something else goes wrong.

 

Fingers crossed for tomorrow or its time to call it a day when the insurance is up.

[JasonR24]

Have you tried the tps and ecu change yet?

[TubbyTwo]

all planned for tomorrow buddy, got a transmission ecu to swap, then going to check the O2 sensor, wiring, TPS sensor etc.

[JasonR24]

all planned for tomorrow buddy, got a transmission ecu to swap, then going to check the O2 sensor, wiring, TPS sensor etc.

 

Hopefully one of those is the problem mate and you'll be done with the problems

[TubbyTwo]

I hope so buddy

[Kristian_Wraae]

What happens is probably that you have an intermittend TPS error that sets the error code and forces the ECU into limp mode (aka the 3000 rpm stuff).

 

Resetting the ECU makes it able to run until the code is set again.

 

Could be wiring or the TPS itself. You need to check those.

[TubbyTwo]

Right tested the O2 sensor quickly tonight it doesnt give a solid reading, its constantly going up and down. readings take on the 20v setting on multimeter:

 

The lowest reading was 0.06v

 

Highest was 0.79v

 

Constantly cycling between the high and low readings with 0.4 and 0.6v showing frequently.

 

So guessing its goosed?

[Kristian_Wraae]

Well the nature of a narrow band is that it constantly changes between high and low indicating if the mixture is lean or rich. It can never be normal - only too much or too little.

[Ian C]

Constantly cycling between the high and low readings with 0.4 and 0.6v showing frequently.

 

That's working just fine, it's always hunting up and down quite rapidly, balancing the fuel mix. A constant reading means it's goosed.

 

Did you test it straight after experiencing the problem?

[mellonman]

i have found that if the readings get to far out they make it rich also IE, 0.2 and 0.8

[TubbyTwo]

That's working just fine, it's always hunting up and down quite rapidly, balancing the fuel mix. A constant reading means it's goosed.

 

Did you test it straight after experiencing the problem?

 

Let the car warm up, took it out for a decent drive to get the oil temp up and sods law it didn't misbehave at all. So tested it. Idle is still to high, from cold it sits at 1900 for a minute then drops to 1100 then down to 900 after that. Think I may need to reset the TPS as per service manual again. Also when its "knobbing about" the vac reading on the ebc gauge goes from -78 to -54 constantly.

[TubbyTwo]

Ok so just reading through the TPS reset procedure:

 

 

 

Top of page 2 it mentions adjusting the TPS until the ohmmeter "deflects" does this mean it reads the same as the values in the table shown on page 2? Want to make sure I get this correct the first time.

 

Going to spend a full day tomorrow testing everything, drove to work this morning with the windows down, round some twisty country lanes and the car has decided to behave itself for the first time in god knows how long. The love is coming back, so have a new lease of enthusiasm to try and sort it.

 

I was also thinking last night, I have a one of hecklers rear fog PCB conversions to the drivers side rear light, could this cause a problem with the brake signal to the ecu if it was corroded/loose wire?

 

Plan tomorrow is:

 

- reset TPS sensor

- swap and test spare transmission ecu

- check TPS and ILD wires to ecu

- check brake signal to ecu

 

Also have a new set of spark plugs to fit and want to check the all the coil pack clips if there is time.

[JasonR24]

Ok so just reading through the TPS reset procedure:

 

http://www.mkivsupra.net/vbb/attachment.php?attachmentid=163488&d=1359038580

 

http://www.mkivsupra.net/vbb/attachment.php?attachmentid=163489&d=1359038580

 

Top of page 2 it mentions adjusting the TPS until the ohmmeter "deflects" does this mean it reads the same as the values in the table shown on page 2? Want to make sure I get this correct the first time.

 

Going to spend a full day tomorrow testing everything, drove to work this morning with the windows down, round some twisty country lanes and the car has decided to behave itself for the first time in god knows how long. The love is coming back, so have a new lease of enthusiasm to try and sort it.

 

I was also thinking last night, I have a one of hecklers rear fog PCB conversions to the drivers side rear light, could this cause a problem with the brake signal to the ecu if it was corroded/loose wire?

 

Plan tomorrow is:

 

- reset TPS sensor

- swap and test spare transmission ecu

- check TPS and ILD wires to ecu

- check brake signal to ecu

 

Also have a new set of spark plugs to fit and want to check the all the coil pack clips if there is time.

 

Sounds like a good plan mate hope you get this sorted! It's worth checking all wiring as its the easiest thing to break or corrode.

[TubbyTwo]

Question is, if I do find one of the wires has an error its going to be a right mission to fix I expect, assume it will be a case of tracing the wire back and cutting the loom open and replacing the whole thing? or just replacing the damaged section.

 

either of those I not particularly enthusiastic about doing.

[JasonR24]

Question is, if I do find one of the wires has an error its going to be a right mission to fix I expect, assume it will be a case of tracing the wire back and cutting the loom open and replacing the whole thing? or just replacing the damaged section.

 

either of those I not particularly enthusiastic about doing.

 

Yea I am just about able to wire and solder speaker cables.... I wouldn't want to mess with the loom myself but I am sure it is possible to repair a damaged wire.

[mellonman]

if you did find a damaged wire you can just repair the damaged part , but might be easy to just run some new wires depending

[TubbyTwo]

Well as expected that didn't go well, failed at testing the TPS sensor itself. due to the angle I cant see to get the multimeter plugs in to even check resistances, I don't really know what I'm looking for with it anyway despite following the testing pages from the manual. I couldn't get any readings so don't know if its the wrong setting on the multimeter or I'm not doing it right. That combined with the fact the bonnet dropped and whacked my head, I got some serious red mist.

 

I'm now sat here deciding what to do with the car, at the end of my teather with it, had to come inside to stop me taking a hammer to it. Its probably just a simple problem but I no longer have the interest or motivation to even wash the car because of the last few months let alone try and fix it.

 

I doubt an average garage could sort the problem, and cant afford another big bill for something that's not going to solve the problem, also any decent specialist is miles away and I don't fancy taking the car on a long road trip in its current state.

 

So at present I'm 99% sure its being broken up the next few weeks, downside is at the moment its my daily drive so I'm just going to get more and more angry with it.