High idle issue

KRISGAJ

MEMBER
1992 MERCEDES BENZ 500SL
5.0L
V8
2WD
AUTOMATIC
40,000 MILES

Hello, I have an issue with a high (around 1,000 rpm's) idle when (and only then) the engine is warm and it is set on P or N. When put on D it goes down to around 700. I have inspected the vacuum and the secondary air hoses. With one exception (I put a picture of the idle control valve hose crack for you to verify if that could cause such symptoms) they all look decent.
Would you have any advice?
Best regards!
Chris

5 Replies

JACOBANDNICKOLAS

MECHANIC
109,747 POSTS

Welcome to 2CarPros.

The idle air control valve is electric and not vacuum actuated. The picture didn't come through, but if you have a crack in any of the vacuum hoses, it will cause problems. Here is a test for checking for vacuum leaks:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

I attached a picture of the IAC location. Is that the component you are referring to?

Let me know if you have other questions.

Take care,
Joe

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Sunday, December 30th, 2018 AT 3:47 PM

KRISGAJ

MEMBER
3 POSTS

Joe,

Thanks for your answer. I have put the pictures of the idle control valve with a cracked hose I mentioned before. I have already ordered a new hose as well as a carburetor cleaner to clean some dirt I noticed in the valve. Do you think this might help?
Greetings!
Chris

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Monday, December 31st, 2018 AT 12:19 AM

JACOBANDNICKOLAS

MECHANIC
109,747 POSTS

Hi and welcome back.

I do feel that will help. Especially if the IAC is dirty. Be careful what you spray with the brake cleaner. It is very aggressive.

Let me know how it works out for you and Happy New Year,

Joe

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Monday, December 31st, 2018 AT 2:53 PM

KRISGAJ