1G throttle position sensor wiring

[iwalton]

Hey folks,
I've got a 1990 TSi that has a good throttle position sensor (checked continuity and resistance), but the computer is not receiving any information. I'm kind of a noob and need this car running for tomorrow, if possible. What is the easiest way to rewire it?

 

[steve]

Two of the four wires are shared with other sensors so without knowing the cause of your current issue it's hard to tell you how to most easily fix it.

The shared are +5v sensor power and sensor ground. The other two wires are the TPS output and the IPS input.

 

[iwalton]

Two of the four wires are shared with other sensors so without knowing the cause of your current issue it's hard to tell you how to most easily fix it.

The shared are +5v sensor power and sensor ground. The other two wires are the TPS output and the IPS input.

Four wires? I only have three coming out of my TPS, unless you are including the connection that mounts right at the throttle cable? And unlike most of the pictures of TPS's I have seen, there isn't a fourth hook-up at the TPS.

A local shop said I could simply run wire to ground, one to power and the other to the ECU? Is this right?

 

[Calan]

Steve may have misread the year of your car.

The 1G TPS has 3 wires (+5v, GND, and TPS output), since the IPS is separate and on the other side of the TB. On a 2g, the IPS is integrated into the TPS, so it has 4 wires as Steve described above. (I assume the '90 TPS is the same as other 1G's, but it may be different since it's a bit odd in other electrical areas).

The shop was wrong. For one thing, the voltage going to the TPS is 5v, not 12v, and for another... it needs to be a regulated voltage so that the TPS output is stable.

I would start by checking for the +5v and sensor ground at the TPS connector, and then start tracing wires. The pinouts can be found in this post by Steve.

 

[steve]

90's are special and have the IPS (Idle Position Switch) wire at the A-55 connector where the pigtail mates with the engine harness. You need to identify is you have the correct signals at the harness side of A-55 and if they reach the ECU.

A-55
Pin 1 IPS Green (to ECU pin 6)
Pin 2 Sensor Ground Green/Black (to ECU pins 17 and 24)
Pin 3 +5v Sensor Power Green/Red (to ECU pin 23)
Pin 4 TPS Green/White (to ECU pin 19)

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[Calan]

Ahhhh...

So does the '90 TPS still have 3 pins, or has his been swapped to a later 1G and the harness modified, based on this:

Four wires? I only have three coming out of my tps,

 

[steve]

Ahhhh...

So does the '90 TPS still have 3 pins, or has his been swapped to a later 1G and the harness modified, based on this:

There are three wires to the TPS but it's my understanding on a 90 that where the pigtail disconnects from the engine wiring harness at A-55 there are all 4 wires. The three that go into the TPS (molded) and the one for the IPS on the other side of the Throttle Body.

It's not like the 91+ TPS where there is a three position connector that the harness plugs into and a wire over to the IPS connector.

Standard disclaimer: I don't own a 90 so I can only go by pictures and the FSM.

 

[iwalton]

Ahhhh...

So does the '90 TPS still have 3 pins, or has his been swapped to a later 1G and the harness modified, based on this:

Great call, man! Yup, I swapped the 1990 turbo engine into a 1994 n/t body. I was dumb, so i kept just the n/t wiring harness and modified it instead.
But, just fyi, the 1994 n/t wiring harness still came with the separate A-55 connector on the opposite side of the throttle body. (I'm not sure if this is specific to the 1994 or just the n/t or what, however)

Thanks for the help, guys. I'll rewire it tonight and see where I get and get back to you.

 

[iwalton]

Ok, so it turns out that the throttle position sensor was wired in right the first time, but I found out that there was some discontinuity in the idle switch, so I rewired that.

But, as soon as I finished that, I got really bad idle surge!!!

I've done a lot of reading into the idle surge problem, and I've already checked the BISS and throttle body, which are both working and clean. I have no vacuum leaks and everything else looks fine. I'm gonna check the ISC to make sure all the electrical issues with it are good....

Any quick thoughts/ideas/tips?