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Re: bmw-digest V2 #171

On Sat, 24 Dec 1994 owner-bmw-digest@domain.elided wrote:

> 
> From: Jay Baudendistel <75212.2155@domain.elided>
> Date: 24 Dec 94 16:51:53 EST
> Subject: 318i idles too fast
> 
> Dear BMW Gurus:
> 
> Please share your wisdom on the idle problem I'm having on my '84 
> 318i.  The car has about 155k miles on it and idles around 1600 rpm 
> both cold and warm.  The car has long history with this problem and 
> the previous owner finally gave up any hope of resolving it. 
 > 
> The service records indicate the following:
> 
> 8k miles   - Poor idle when cold - 500 to 1800 rpm.  Replace plugs, 
>              reset timing, adj. milliamps, cleaned idle valve.
> 23k miles  - Engine cycles while idling (since last adjust 3 weeks ago) 
>              Especially when cold - poss. needs decarbonizing.
> 30k miles  - Engine cycles when cold - Decarbonize valves.
>              With warmer weather, eng. stalls - Replace idle valve & 
>              Box(?), Adjust CO mixture & milliamps.
> 69k miles  - Idle cycles when car is first started - set CO.
> 71k miles  - When cold, car idles at 1400 rpm - set engine specs, 
>              adjust milliamps EFI.
> 79k miles  - Idle surges about 300 rpm - Troubleshoot idle system, 
>              defective oxygen sensor, replaced sensor, set milliamps. 
> 86k miles  - Rough idle when cold thru warm up phase - set engine to 
>              specs, clean and lubricate idle valve.
> 92k miles  - Engine idles 1200-1400 rpm when engine is warm - reset 
>              milliamps to specs, EFI.
> 131k miles - Idles too fast (No condition was noticed by mechanic) -
>              Cleaned linkage & made visual checks.
> 138k miles - Sold car
> 
> It seems to me that the car's idle started acting up on me when the 
> whether started getting cooler a couple of months ago.  I checked the 
> coolant temperature sensor - 1360 ohms at 56 degrees F, idles around 
> 1600 rpm - 291 ohms with engine warm, idles around 1600 rpm.  The 
> applied voltage to the sensor is about 1.7V.  The Haynes manual states 
> the sensor's thermistor should produce 2100-2900 ohms when cold and 
> 270-400 ohms when warm.  Although the resistance reading is too low 
> when cold, it is within the correct range when warm.  Therefore, when 
> the engine is warm, I cannot attribute the fast idle to the sensor. 
> 
> I also checked the idle control valve per directions from the Haynes 
> manual: 
> 1. The valve should be "vibrating and humming slightly" with 
>    the engine running.  The valve doesn't vibrate or hum at all. 
> 2. Removing the electrical connector from the valve should produce an 
>    idle of 2000 rpm.  It does. 
> 3. Resistance across the valve terminals should be between 9 and 10 
>    ohms.  I received a reading of 10.6 ohms which seems close enough. 
> 4. Battery voltage applied to the valve should close it tightly.
>    It does closes tightly.
> 5. An ammeter placed in series with the valve should read 400-500mA at 
>    idle. It reads 560mA at 1600 rpm but will drop to within specs when 
>    I reduce the idle by pinching closed the hose from the valve to the 
>    intake manifold.  It seems that the control current is correct. 
> 
> I believe the problem stems from a bad idle control valve because;
> 1.  The valve does not seem to vibrate or hum.
> 2.  I can reduce the idle by pinching off the hose from the valve to 
>     the intake manifold.  (I can even make the engine stall this way.) 
> 
> Before I spend $175 to replace the idle control valve, I wanted to ask 
> if anyone on the list has experience with this reoccurring problem.  
> Is it typical for this valve to cause such a maintenance problem over 
> the lifetime of the car?  Jeez, its been replaced once (that I know 
> of) already.  Any other ideas?
> 
> By the way, the oxygen sensor is putting out the correct voltage, I've 
> found no vacuum leaks, and the timing centrifugal advance is operating 
> normally. 
> 
> One more thing.  How do I adjust the C.O. on this car?  Is there an 
> ajustment screw I can twist?  I haven't found anything in the Haynes 
> manual about this adjustment. 
> 
> Please forgive me for the length of this posting.  I wanted to give 
> as much information as possible.                                
> 
> Sincerely,
> 
> Jay Baudendistel
> 75212.2155@domain.elided
> 
I am the owner of a 84 318i also.  I can assure that this is due to the 
Idle Control Valve.  You descrive EXACTALLY the same symptoms my car had 
about 2 years ago.  My BOSCH dealer replaced the idle control valve and 
viola' it fixed the problem.  I say go ahead.  You are right.

DH