When warm, idle fluctuates between 600 and 1100 rpm and occasionally stalls out. Full tune up ($$$) three months ago.

Can idle control valve/idle speed stabilizer fail? Local mech charged for cleaning same but problem persists.

What was changed in the tune up? To start I would inspect all the vacuum and rubber IAC hoses for cracks and leaks.

__________________
1989 300CE

Mech replaced plugs, wires, cap etc., the usual.

Car was running fine when he finished. Idle problem developed in the last 10 days.

Do you know what type of plugs were used?

__________________
1989 300CE

No, not offhand. One of the reasons I have patronized this shop for over 20 years is because he uses only quality benz approved parts and is favored by owners of fine cars in the area. Last week, when I picked up my car there was a restored '58 Jag XK150 waiting for his attention. Knocked the socks off!!!