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Re: K-jet Idle Problem

* Paul King Wrote -----------------------------------------------------------
 
{Tales of Bad Idle behavior deleted}
 
> I have the Bosch Injection manual by Bentley, and also the Haynes manual for
> the car.  The trouble shooting sections of the manuals tell you to check the
> following parts when you have idle problems:
> 
> *  Accelerator cable or throttle valve binding -- Checked, OK
> *  Accelerator stop out of adjustment -- OK

Probably would not cause wandering idle

> *  Vacuum system leaking -- removing the dipstick while engine is running
> stalls the engine, so I believe there is no leak -- OK.

This test for an idle leak is useless.  Really check all the vaccuum hoses
for cracks (maybe even replace them), check the air bellows from the fuel
distributor to the intake manifold for cracks, carefully check the pcv
hose from the valve cover to the intake manifold.  Spray some carb.
cleaner around the fuel injectors and see if the idle changes (checking
for bad Fuel injector seals). 

> *  Clogged Fuel filter -- OK
Extremely Unlikely.

> *  Air sensor/baffle plate binding or out of adjustment -- checked, OK
> *  Auxilary air valve faulty -- I haven't been able to check this 100%, but
> the cold start works great and settles down upon warm up, so I don't think
> this is the problem.  Also, it is the type that is coolant temperature
> operated, so electrical problems are ruled out. (probably OK)

Also unlikely

> *  Incorrect mixture -- I had the car in the shop for this problem, and 
they
> said that the mixture was way too lean.  However the problem returned an hour
> later (unfortunately, my $45 didn't  :(   ).  OK

> I cannot find anything wrong, and I don't want to start just randomly
> replacing special order/expensive parts.  The car acts as if the sensor plate
> stays up until you get below a certain rpm, and then it quickly falls at a
> point and reduces the rpms all at once.
> 
> One area I haven't checked is the ignition.  Is it possible that the advance
> on the distributor is kicking in too early and throwing off the idle?

Very possible that the distributor is messing up since I have had this
happen.  Didn't really notice it until I was setting the timing this past
spring and the car ran like crap afterwards when I reconnected all the
vaccuum lines and took it for a test drive.  The vaccuum canister would
stick in random locations even with the vaccuum lines disconnected. 

I don't know if the latter 320i had these but I had a problem with the
start air valve sticking open. It's one of the two vacuum diaphragms (sp?)
(the one with a vaccuum line connected to it) connected to the fuel
distributor bellows that bypasses the throttle plate and provides extra
air when the car is starting.  The other diaphragm is the vaccuum limiter
that limits manifold vaccuum to a preset value.  My start air valve
started randomly sticking and caused the idle to do all sorts of random
things (like idle at 3000 rpm sometimes but idle normal other times).  I
checked it by squeezing the hose to the manifold (not the vaccuum line but
the air hose) to cut off the air flow through it when the car was idleing
high and the idle went back to normal. Never got around to replacing it
(Its been 5 years now), I just plugged it up but the car idles fine now.
(I have to crack the throttle open now on cold days for the car to start). 

Hope this helps.

*******************************************************************************
Walt Barie ([email protected], [email protected])
Graduate Student
Dept. of Electrical Engineering, University of Pittsburgh

'79 320i DSP Solo II and Drivers School Car
'80 528i

    "You gotta first spin the dice in order to win the game" - esp '95

Of course what I say in no way reflects the views of the University....
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