Hello Denrac,

and many thanks for your input.

'The flap is to increase the vacuum in the intake manifold when the EGR valve opens. '

I suppose when the flap closes the engine is left with no other choice that to draw from the exhaust more. Thus EGR. Am I correct? So when I rev up the flap closes not to protect the system from too much pressure but to recirc exhaust gasses more?

'On the 1992 602, the flap operates in tandem with the wastegate : when vacuum is applied to the flap, the flap closes, no vacuum goes to the wastegate, the wastegate is open and no turbo boost is builded. At the same time, the EGR valve opens and more exhaust gaz is recirculated.'

Now EGR valve and wastegate are 2 separate items? If so, where is the wastegate? The only thing I can see is the flap in intake and EGR valve that interconnects exhaust to intake above where the flap is.

'The EDS knows that the EGR is functionning when it sees by mean of the MAF sensor a reduction of fresh air admitted in the engine. '

So there is an active component in the system - a sensor. Do you have an idea where the sensor is? I haven't spotted it yet. Naturally, I haven't really looked for it either.

'Overboost is controlled by the same set of components : when pressure is too high, the flap is closed and the wastegate is opened and the EDS sees a rapid drop in fresh air admitted.'

This leaves me with a question - where is the wastegate? Do you mean the EGR valve? With the valve open the excessive pressure could escape to exhaust through the interconnection I described above. Is this it?

'When one of the component is not doing its job, the EDS cut all the vacuum to the wastegate in order to protect the engine. That's why you cannot just block the EGR valve on a 602.'

That would men the wastegate is in open position so that no sufficient pressure can build up? Speaking of which, I only unplugged the EGR valve and the car was felt faster. Apparently the turbo never worked so there could be no difference (but I can feel kick it in at approx. 1900 RMP) or no boost was cut no matter that EGR valve was disconnected.

'When the engine is idling, the wastegate and the EGR valve should be closed, and the flap wide opened. '

Flap is open. Now I see the wastegate is a different object to that EGR valve I unplugged. Forgive me for not knowing - where can it be located on the turbo?

'The EDS unit stores error codes : plugging and unplugging various component can leave you without turbo boost until you erase the stored fault.'

I had code 11, had it reset. Now it's code 1 - everything OK. I don't think I would be left with unoperational turbo though - the memory only stores codes. Or so I think. One way or the other - even with valve unplugged I had turbo operational.