Do I need an Idle Control Valve???

[mike_in_tulsa]

I just bought a 1985 735i with an automatic transmission. The engine revs up and back down continuously when it should be idling. The guy I bought it from said it needed an Idle Control Valve. I priced one for $139 at Autozone, so before I went and bought it, I wanted to ask the members of this forum if they thought that this sounds like what I need. If so, is it a hard part to install? Also, the transmission is causing the engine to rev up between gear shifts. Could this also be caused by the bad idle control valve? I thought that it might since the engine keeps revving up and back down and maybe the transmissions is getting mixed signals from the engine about rpms. I would appreciate any input from this forum about both of these problems. Thanks.

[libertylover]

Before you buy a new Idle Control Valve you should check for air leaks in the system. Even if you replace the idle valve, the engine will never run right if there are air leaks.

The Idle Control Valve, the Mass Airflow Sensor, Air Intake Temperature sensor, etc. all need accurate information in order to do thier jobs as designed as this means the air flowing over them is only from a controlled source. Check the hoses and tubing that connect between the air filter, the sensors, and the intake manifold to make sure all of the gaskets are in good shape.

You should also make sure that air does not leak into the Intake Manifold. On a 1985 car, if the Intake Manifold gaskets have never been changed there is a high probability that they leak air. Some say to spray Fuel Injection cleaner around the base of the Intake Manifold and if you hear a change in the engine it means the gaskets are leaking (Be careful not to spray into any electronics.). Good luck.