low on performance and high idle

[hayesey]

it's called an auxiliary air valve usually, people often call it an idle stabilisation valve but that's not really what it is.

[g40Ross]

it's called an auxiliary air valve usually, people often call it an idle stabilisation valve but that's not really what it is.

thanks for that mate! iv just been back to my local vw dealers having found the part number and the isv is not far off £100 cos they have to be made to order! is that right?

cheers

Ross

[hayesey]

yeah they're not cheap, people usually just clean them out by removing them and soaking in petrol for a bit. 

[G40supercharged]

I'm pretty sure the auxiliary air valve thing only works when the engine is cold/warming up. I could completely clamp the hose from the valve to manifold shut on my G40 and it had no affect on idle. I would just try cleaning it out first. It's actually the ECU that stabilises the idle by adjusting the timing. If you have the base timing set wrong or too much/too little air going in with the idle trim screw on the throttle body it will tend to have an unstable idle. You can't just change the settings as you are constantly fighting the ECU. You need to disconnect the blue temperature sensor with the car nicely warmed up (only disconnect this when the engine is running to avoid logging faults). This puts ithe ECU into service set mode. Then adjust base timing and idle trim screw as required. Then put back blue temp sensor and ECU will take over again.   

[hayesey]

yeah it is supposed to only work when warming up but when they get gummed up or just fail they can open at any time causing a dodgy idle because there's just too much air getting in to idle properly at normal running temps.

[g40Ross]

I'm pretty sure the auxiliary air valve thing only works when the engine is cold/warming up. I could completely clamp the hose from the valve to manifold shut on my G40 and it had no affect on idle. I would just try cleaning it out first. It's actually the ECU that stabilises the idle by adjusting the timing. If you have the base timing set wrong or too much/too little air going in with the idle trim screw on the throttle body it will tend to have an unstable idle. You can't just change the settings as you are constantly fighting the ECU. You need to disconnect the blue temperature sensor with the car nicely warmed up (only disconnect this when the engine is running to avoid logging faults). This puts ithe ECU into service set mode. Then adjust base timing and idle trim screw as required. Then put back blue temp sensor and ECU will take over again.   

ive replaced the blue temp sensor! if i do what you say about removing the blue temp sensor will the car start to idle higher?

cheers

Ross

[G40supercharged]

By disconnecting the blue temperature sensor I mean just take the connector off. The blue temperature sensor normally has a fairly low resistance. When you disconnect it with the engine running the ECU sees an open circuit (very high resistance) and that tells it to go into service mode. (If you start the car with it already disconnected the ECU will just think the sensor is broken.) The idle speed may go up or down when the sensor is disconnected; the point is that the ECU will no longer be trying to adjust the idle speed, so the idle should stay at the same revs. You can then adjust it as you like using the idle screw on the throttle body (something like 1000rpm would be OK). You have to set the timing like this as well, otherwise the ECU is constantly adjusting it.

So: engine running and fully warm, disconnect blue sensor, set idle to factory spec with timing strobe, set idle speed to factory spec, reconnect blue sensor. It should then be nice and stable at factory idle speed (which is programmed into the ECU).

[g40Ross]

nice one cheers matey!

[G40supercharged]

I've just re-read that and it should be "set timing to factory spec with timing strobe" rather than "set idle to factory spec with timing strobe"

[g40Ross]

I've just re-read that and it should be "set timing to factory spec with timing strobe" rather than "set idle to factory spec with timing strobe"

whats the timing strobe?

[Puncharado]

whats the timing strobe?

Engine timing light. It's connected to no.1 plug lead, so it flashes each time that plug sparks. So with the engine running, when the light is aimed at the pullley the timing mark on the pulley appears to be stationary. The distributor is then adjusted until the mark on the pulley lines up with the pointer on the engine. The timing marks are easier to see if you put something white on them, like tippex or chalk. But make sure the mechanical timing is right first.