Re: Erratic idle

[Jim Cash <j.cash@xxxxxxxxxxxx>]

Ed Fens writes:

> I have an '84 528e with 5 speed. The car idles perfect (750 RPM) with the air
> conditioner OFF.
> 
> However, once I turn the A/C ON, it immediately starts to idle at 1100 RPM,
> and constantly surges to 1500 RPM.
> 
> 25,000 miles ago I replaced the Idle Control Valve.  The Idle Control Module,
> however, is still the original, as is the Motronic computer.  
> 
> Any ideas what's wrong with the idling?




Ed

I prefer "Erotic Idols" myself, but each to his own poison.


When you turn on the A/C that applies a battery signal to the idle
control module which then boosts the idle slightly to help overcome the
drag of the A/C. But it should not go that high (900 maybe - I no longer
have the diagrams etc.) And it should not surge.


It sounds like the unit is getting the signal from the A/C, but I
suspect one of 2 issues.


You say you replaced the idle control valve, but not the electronic
control module. There were several versions of these in the early mid
1980's - I had idle surge problems on my 1982 528eA (only during the
warm up period) until the idle electronics & valve were replaced with
the 1985 versions.

You may have a control unit that is designed for a different valve - you
will have to check that out with a knowledgeable BMW tech/parts guy.


Second - setting up the idle control valve properly is a bit of a
science - which I never did myself since the dealer did the leg work to
fix the problem. But I have seen some people on the digest describe the
procedure - you need a current meter on the valve as you set the control
screw, and you need to make sure the CO levels are set correctly first.
Also need to make sure you have no vacuum leaks in the intake system
anywhere. Even a loose oil fill cap or dipstick seal will make a
difference.


Hope that helps.

Cheers

Jim Cash
London, Ontario, Canada
BMW CCA 102929

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