7A wiring issues...

[RS2]

I've been driving my VW Transporter Tristar Crewcab around for a couple of months now with the 7A running fairly well.

I still have a couple of faults in the ECU though.

First is the lack of VSS (speed sensor). Easy fix and one I'll get to eventually.

The other is an idle switch error.

I've checked the switch (works fine) and that the cable has enough slack for the throttle to be sitting against it's stop to activate the switch.

So onto the wiring.

I bought this engine from a fellow S2 forum member who had removed the engine and loom himself. To be honest, I bought what I thought was a complete setup but quickly realised that I was missing many parts so it's entirely possible that I'm missing more parts!!

Checking the wiring from the idle swich (2 x wires, 1 x brown which is connected to earth and 1 x yellow/grey) to into the loom, I've realised that the yellow/grey wire connects to another wire that is in the engine bay (which is not used as I believe that it went to a pressure switch on the brake bomb) and then it goes into a connector block which is not connected to anything!! So the idle position switch is not connected hence the ECU error.

This is the connector block.



Also among other connectors that aren't connected up to anything, I have one which is connected to the ECU but not to anything else and I've no idea what it should be connected to.

Any ideas?



So... how does the idle position switch connect to the ECU and which wire to which plug (my ECU is the later 4 plug ECU) should it connect to?

I have been given this ECU diagram from a fellow Audi nut on Motorgeek forums.



MG

[Error404]

The top picture, T10 and T5 connectors are used to integrate with the dash harness. The second is the output connector for the aux gauges. Sounds like you have something odd going on, as the separate idle switch is only used on the early 7A, with 2 plug ECU. Your 4 plug ECU should use a TPS with integrated idle switch. HTH

[RS2]

The top picture, T10 and T5 connectors are used to integrate with the dash harness. The second is the output connector for the aux gauges. Sounds like you have something odd going on, as the separate idle switch is only used on the early 7A, with 2 plug ECU. Your 4 plug ECU should use a TPS with integrated idle switch. HTH

Hmmm... that's odd.

The throttle body was one of the things that I was missing when I bought the engine. I bought it from another fellow S2 member as the correct one for the late engine.

The loom has a plug to fit to the idle switch but I guess that could just be a plug for something else that isn't used in the engine bay due to the conversion.

This is the throttle body.



The throttle position sensor plugs in perfectly. Do they share the same plug but less/more wires with early to late?

Thanks for your reply

MG

[Error404]

Yeah thats not the plug for the idle switch, hard to tell I think its probably for the brake fluid level warning.
You need the later throttle body with the (IIRC Bosch) TPS or you can identify the idle switch wire in the TPS switch and modify the harness to suit. HTH

[RS2]

Yeah thats not the plug for the idle switch, hard to tell I think its probably for the brake fluid level warning.
You need the later throttle body with the (IIRC Bosch) TPS or you can identify the idle switch wire in the TPS switch and modify the harness to suit. HTH

****... Ok thanks for the info. Yet another part to buy for this engine!

I'm surprised about it having a Bosch TPS. The ECU is Hitachi.



MG

[Error404]

Yeah I could be wrong, might be Hitachi. But it is definitely a different TPS p/n that you need

[simon20vq]

Two systems on that motor, I think I have ecu's for both and maybe throttle bodies if you need anything drop me a PM.

[RS2]

Right I think I have this figured out.

From what I've posted above, it looks like I'm saying that my throttle body has a separate idle switch. It doesn't. My bad... Sorry.

So I have the correct throttle body.

The connector that I had plugged in is identical in every way to the correct connector which was not plugged in! I flagged up that I had this other spare connector in another post a while ago with wire colours but if you're not familiar with the exact wire colours, you wouldn't know.

I've been using a wiring diagram for a different engine in the Audi 90 which was similar but not correct hence the lack of wire colour knowledge.

Next time, I'll take the engine out myself!

Thanks all for your help.

Sorry for being a muppet

MG

[Bowie69]

There's two connectors there, one is the air temp sender, and the other for the idle switch, as you now know, which has a short jumper cable going to the TPS/Switch on the underside of the throttle body.

If you need any other wiring locations checking I have my running 7A parked just outside most of the time...

[RS2]

There's two connectors there, one is the air temp sender, and the other for the idle switch, as you now know, which has a short jumper cable going to the TPS/Switch on the underside of the throttle body.

If you need any other wiring locations checking I have my running 7A parked just outside most of the time...

Thanks.

The engine is now running fairly well but as I set up the CO% in it when the idle switch wasn't plugged in I recon that I need to reset the CO% again and see how things go.

It's more settled at idle now but has a tendency to drop a little low in rpms when coming off the throttle.

I may have adjusted the idle speed down a little low as it was very high once I'd plugged everything back in as it should be.

MG

[Bowie69]

Did you go through the later car's idle speed adjustment with the carbon canister unplugged and fuse in the fuel pump relay?

[RS2]

Carbon canister? On this engine in my van ..

I'm just adjusting it until it's around 800-850rpm.

What's the correct procedure?

MG

[Bowie69]

Post March 1990 production date:

Remove rear electrical connector from carbon canister shutoff valve.
With engine idling and all accessories off, install spare fuse in the top of the fuel pump relay.
Adjust idle speed to spec at adjusting screw on throttle body (accel.cable is sticking out of it, adj. screw is pointing approx.to the air cleaner).

Nicked from 20V.org.

By putting the fuse in the FPR it fixes the idle valve position so you can set the 'base' idle properly, rather than having it automatically regulating it all the time....

[RS2]

Post March 1990 production date:

Remove rear electrical connector from carbon canister shutoff valve.
With engine idling and all accessories off, install spare fuse in the top of the fuel pump relay.
Adjust idle speed to spec at adjusting screw on throttle body (accel.cable is sticking out of it, adj. screw is pointing approx.to the air cleaner).

Nicked from 20V.org.

By putting the fuse in the FPR it fixes the idle valve position so you can set the 'base' idle properly, rather than having it automatically regulating it all the time....

Thanks.

What should the idle rpm be?

MG

[Bowie69]

Apparently 800rpm, but I think the rev counter on most cars is pretty inaccurate, mine looks to be around 900, but any lower than that and it doesn't feel smooth.

If you have a timing light with a tach gauge on it I would do that