How do you check to see if this valve is working correctly? I pulled the two wire plug off and it is getting 4.5 volts. Does this valve move back and fourth? 89420sel ideling at 1100 rpms in neutral and hot.

THE ENGINE IS NOT RUNNING HOT,I MEAN AT NORMAL RUNNING TEMP.I CHECKED THE 10AMP FUSE AND IT IS OK,THE THROTTLE VALVE SWITCH HAS BEEN REPLACED.

Would the cold start valve malfunctioning do this? Sorry to answer your question with a question.

Another thing you may wish to investigate is an air leak downstream of valve. More air coming in makes the idle speed increase. Could it be when the switch was replaced something was moved or not put back on? Or one of the air hoses is brittle with age and has a crack or cannot seal properly anymore?

Good luck!

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1989 560SEL (172k)
1989 325IC (122K)
2004 Suzuki Volusia LE (3500 miles)
2005 Yamaha Road Star (20 K miles)

I have have the same problem with both of my 420's. In one case I tried to clean the valve using brake cleaner (a good solvent) but it didnt do any good. I ended up buying a new valve and the problem was fixed. However, these valves are way expensive. So on the other car I spent a lot of time cleaning the valve. This time I used carburator / choke cleaner. It did a better job of disolving the carbon junk. I kept working on it until I could not get any more junk out. I was surprised how much stuff came out. I spent almost 2 hours soaking, spraying, and repeating the process. To my surprise, it did fix the problem. I also replaced both of the hoses since they were hard. On hind sight, I should have spent more time on the first one and I would not have had to spend the $ to buy a new one. Live and learn.

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I got too many cars!! Insurance eats me alive. Dave

78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k