940 1994 Questions re idle speed

Post by **writer100** » 01 Feb 2010, 10:30

Hello,

As a maintenance procedure, I am planning to clean my throttle body. I was wondering what the cold/warm idle speed is supposed to be, as it may change after the cleaning. It currently appears to be around 600 rpm. The engine runs just fine.

I also notice that the tach is a little twitchy and jerks around. For instance, sometimes it reads 0 rpm when the engine is running. Again, the engine runs fine--it is just the tach. Any ideas what causes this?

Should I also clean my Mass Airflow Sensor, or is this risky?

Thanks for your suggestions,

Alex

Post by **billofdurham** » 01 Feb 2010, 12:24

The idle speed should be 775rpm. It is not adjustable as it is controlled by the ECU. Cleaning the throttle body should bring it nearer to the correct speed.

Clean the MAF sensor with a proprietary cleaning spray. It is self cleaning, in theory, but sometimes needs a little help.

The tach problem could be a bad connection at the instrument panel.

Bill.

Post by **writer100** » 01 Feb 2010, 14:20

Bill,

Thanks. By "proprietary" do you mean Volvo? I was planning to use CRC brand MAF cleaner for the MAF.

But I was planning to do the TB and MAF separately just to avoid confusion if there are issues.

In past cars, I believe the tach got its pickup from the rotor. Is this true of Volvo, and could the rotor be an issue re this problem?

Thanks,

Alex

Post by **billofdurham** » 02 Feb 2010, 11:52

Sorry about the confusion. Proprietary means something made for the job by a specialist company. I have heard of owners using WD40, switch cleaner and even methylated spirits to clean the MAF.

We rarely advise members to buy this type of Volvo product. CRC is good.

Bill.

Post by **writer100** » 03 Feb 2010, 10:24

Bill,

Thanks. I will let you know how this goes.

By the way, in the 80's I spent a year in England at the University of Kent. I have fond memories of the beer and the desserts.

Post by **billofdurham** » 03 Feb 2010, 11:54

I have fond memories of the beer and the desserts.

I have a very good friend from the US, now resident over here, and that is the reason she likes living here. When we go out for a meal she has a main course and two desserts.

Keep us posted.

Bill.