Throttle position sensor.

[paulh]

Hi everyone, had a bit of a problem with my mr2. Over the past few days the cars been acting very strange, during gear change when you go back on the gas she's been sort of pausing causing gear changes to be very jerky. Then yesterday this problem progressed to the car not being able to exellerate to more than 2k rpm at which point the revs would cut out back down to 900rpm and with your foot on the floor it would just repeat this cycle. So I disconnected the throttle position sensor which has stopped the problem, I then changed the sensor for another one I had lying around but the problem persists. Has anyone got any ideas to what my problem could be? Any advice would be great!

Cheers Paul.

[boondougal]

Have you used the diagnostic point to see if any fault codes flash?

[paulh]

Yes the car is showing no fault codes, it seems very strange.

[stenky]

Idle is ok? Doesnt choke?

[boondougal]

Just thinking this through if taking the TPS off meant that you could freely rev the car then i would take a close look at the throttle cable.

The cable on mine frayed badly inside the sleeve and would get caught and do something similar to what you describe.

Might be a 2 person job to see what happening but also check the connection at the pedal end.

You can get new / second hand ones but i simply bought a length of new inner cable, threaded it through and used 2 screw type brake cable ends... fair few people have done it that way.


Just reading your original post back can you freely rev the car with the TPS on but the cable disconnected? I obviously mean by moving the mechanism by hand.

[paulh]

Well idle is a little high now with the tps lead unplugged. But yes car revs freely with tps lead unplugged but will not when I reconnect the lead.

[JMR_AW11]

Hi everyone, had a bit of a problem with my mr2. Over the past few days the cars been acting very strange, during gear change when you go back on the gas she's been sort of pausing causing gear changes to be very jerky. Then yesterday this problem progressed to the car not being able to exellerate to more than 2k rpm at which point the revs would cut out back down to 900rpm and with your foot on the floor it would just repeat this cycle. So I disconnected the throttle position sensor which has stopped the problem, I then changed the sensor for another one I had lying around but the problem persists. Has anyone got any ideas to what my problem could be? Any advice would be great!

Cheers Paul.

Sounds like you are hitting fuel cut because the car/ECU is stuck thinking it is in idle mode.

This would happen if the IDL switch contacts in the TPS (or the feed wires) were stuck in the idle position. This faulty IDL switch makes the ECU think the throttle is still at a very low setting. i.e hardly touched at all despite the TPS wiper voltage saying otherwise.

If you find a way of revving the car in this mode then it will rev to about 2k rpm and then cut the fuel injectors off. The ECU will allow the injectors to operate again once the engine revs fall to a normal idle speed and the process will start again where it revs up and cuts out at 2k rpm.

You can get the same effect if the cold start valve plays up. But in your case I think your IDL micro switch contacts in the TPS module are stuck in idle mode even if you press the throttle a lot.

There's two things inside the TPS. There's the variable wiper that indicates throttle position to the ECU plus the IDL contact switch. Your switch must be stuck or very badly adjusted?

You won't get an error code with this IDL switch fault if it is stuck in the idle position. You would get an error if the switch was stuck the other way though. However, you will almost certainly get an error if you remove the entire TPS unit because it should then flag a TPS wiper error.

[paulh]

Great piece of knowledge thanks a lot! I've already changed the tps once and the problem continued so you think the problem could be in the wiring connecting to the tps?

[JMR_AW11]

It does seem odd that you've replaced one TPS already and the car is still faulty (yet it kind of works without the TPS unit!)

From memory the IDL wire from the TPS to the ECU sets a logic level back at the ECU connector on the IDL pin.

I really can't remember for sure but the IDL switch probably pulls the logic level to a logic 0 on the relevant ECU pin when the throttle is closed. It should go to 5V when you press the throttle? Sorry I can't be more precise as I haven't looked at this stuff in many years...

Maybe there is a problem with a wire somewhere that stops the IDL switch/wire from pulling the ECU IDL pin up to 5V when the throttle is pressed. i.e. something is holding the wire at a low voltage and fooling the ECU?

You could check this logic level at the IDL pin on the ECU with the TPS fitted and not fitted? Does it change state or is it stuck at one voltage state?
Does it change state when you press the throttle?

Also check the 5V reference voltage pin on the ECU (pin VCC?) is at 5V with and without the TPS fitted.

This all assumes I've interpreted your car's symptoms correctly

[JMR_AW11]

You could try a quick method of checking the IDL switch health with the procedure below:

Check for error codes in the normal way and I assume there will be no code 11 stored. If there is then clear all codes and try again.

Then repeat the error code procedure but do it with the throttle pressed down before you connect the T to E1 wire (keep the engine off)

On a healthy car I think this will cause a code 11 error because the IDL switch is 'open' on a healthy car with the throttle pressed and the IDL voltage will be at 5V and the ECU will see this as a faulty IDL switch (it is expecting a closed throttle and 0V at IDL during the error code procedure).


Can anyone else confirm this is correct please?

[jimi]

I've already changed the tps once and the problem continued

Did you set it up properly when you changed it ?

[PW@Woodsport]

Paul came to the garage one day (waxstat issues) with a second hand throttle body from a breaker, which i fitted for him and all was well, i didn't set the TPS because it hadn't been touched and the car ran perfectly after that.

This new TPS behaviour is a new fault. Paul pop it down sometime and i'll sort it our for you, it's very difficult to diagnose over forums, but with hands on i'll fix it for you within an hour.

[boondougal]

Paul came to the garage one day (waxstat issues) with a second hand throttle body from a breaker, which i fitted for him and all was well, i didn't set the TPS because it hadn't been touched and the car ran perfectly after that.

This new TPS behaviour is a new fault. Paul pop it down sometime and i'll sort it our for you, it's very difficult to diagnose over forums, but with hands on i'll fix it for you within an hour.

Surely the only benefit to leaving that far north.... PW on your door step

[PW@Woodsport]

Let's nit forget cheap beer and cheap women

[jimi]

Let's nit forget cheap beer and cheap women

and your miles away from southerners

[boondougal]

Let's nit forget cheap beer and cheap women

One word that is associated with both of the above... "Dirty", hence i never go near cheap Beer!

[paulh]

Thanks for everyone's help but with my mechanical knowledge I'll never sort it over the forum on my own . Cheers Paul i'm sorry this is becoming a bit of a habit lol I'll pop over some time next week if your not too busy?

[PW@Woodsport]

I'm always flat out busy mate but you're obviously in a pickle, drop in with it and i'll see what i can do, with any luck it will be a free 10 minute repair

[paulh]

Okay mate thanks a lot