73 280SE 4.5 high idle

[Ansel Allen]

I brought a used 280SE 4.5 about ten years ago and I had the top end reconditioned. It idled high when I brought the car and it still idleds high after the maintenance. The mechanic was adding and removing washers from a valve located in the front of the engine. He mentioned the name of the part, but I was not paying attention. I'm thinking of selling the car and want the new owner to be aware of this condition Can anyone think of what component would cause the engine to idle high or low with this manual adjustments.

[Graham]

Originally Posted by Ansel Allen

I brought a used 280SE 4.5 about ten years ago and I had the top end reconditioned. It idled high when I brought the car and it still idleds high after the maintenance. The mechanic was adding and removing washers from a valve located in the front of the engine. He mentioned the name of the part, but I was not paying attention. I'm thinking of selling the car and want the new owner to be aware of this condition Can anyone think of what component would cause the engine to idle high or low with this manual adjustments.

It's likely the Auxilliary Air Valve (AAV). It allows additional air during start-up. As engine warms up, it has a thermostatic bulb that causes the valve to close. It should be fully closed at 150degF. These valves are prone to sticking and not closing properly. Putting washers in to limit flow is something some do, but does not fix the problem. The valve either needs to be replaced with new or good used one(new ones are very expensive) or dismantled and repaired. It looks like this when disassembled:

[Ansel Allen]

Thanks.

[Ansel Allen]

I need an Auxiliary Air Valve (AAV) for my 1973 280SE 4.5. Can they be rebuilt? or can they be purchased new thru Mercedes Benz. My car runs O.K. but it always idle high. Does any one have a part number for the AAV.

[Frank Reiner]

AA:

Graham gave you a correct, and very satisfactory, answer in your first thread of the same heading. Suggest you delete this thread, and follow up in the first one.

[Graham]

RE part number you asked for in your other thread:

Bosch 0280140017 MB 0001410325

There are repair discussions on Benzworld 107 forums in stickies. Do a search and you will find them. For start wash the valve in solvent then Simple Green or similar and cycle it back & forth with hot/cold water until it it moves and is closed at 150F

[berfinroy]

A little lubrication of moving parts with WD 40 helps.