Since short my 914 - 1972 - 1.7 ltr does not return after starting to the stationairy RPM's around 900/950 but remains at high RPM 1500/1600
Where do I have to look or check to repais this ?

Assuming d-jet, stock, first stop would be the AAR. Sounds like a vacuum leak. About 6mm or so in size. Check all your vacuum hoses as a first move.if your AAR is stuck open, 1600 sounds about right though.

A quick way to check that is just warm it up and then plug the hose that goes from the air cleaner to the regulator.

https://www.pelicanparts.com/914/Parts/Fuel...ayout_large.htm

when i first got my car i had the same issue, high idle, and the areas that are the main cause of vac leaks will be an open AAR, disconnected or bad vac lines, or leaks between the throttle body and plenum, or the intake runners, also cold start valve location.

Also if it is running lean you will have a higher idle.

Order new Vac line kit from AAtlanta and get the new gaskets for all above. .

Good luck, should be able to sort that our fairlly quickly.

Phil

As others have said, likely a vacuum leak. Verify the hoses are connected correctly. Also make sure timing and valves are set right.
Other possibilities include throttle body idle adjustment screw out too far, computer enrichment knob set too rich (clockwise= more rich and knob should generally be within 1-2 clicks of the middle position), and the throttle position sensor is calibrated correctly.

All the above assumes you have the original FI and all parts are correct for your car..

And/Or too much advance.

Easiest way to find the leak is to remove all vacuum lines from the plenum and tape them off .
Start car
Does it now idle properly?

With patience, reconnect one line, start car, does it idle?
Continue one at a time until you find the source of the leak.

The other possible issue is the 50 year old grease in between the distributor advance plates now acts like glue.
Remove and clean those plates, regrease with wheel bearing grease.

Rich