I found my air leak by using Starting Fluid, with small tube extension, to squirt around the edges of the manifold and vacuum fittings. Try the EGR valve, hoses and bracket attachement to the intake manifold. I had lost a bolt.

Starting Fluid is VERY flammable. So is Carb Cleaner. Do not start until you have a fire extingusher close and ready. Carb cleaner will eat paint. Do a little area at a time and listen for idle changes.
This is risky business. If you are not comfortable with accepting the risk -- Don't do it.

Our engine intake gaskets have a history of leaking in a number of car brands.

Good luck , Roy