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Re: control unit blues


Rough idle can be caused by a dirty idle stabilizer valve and/or vacuum
leaks.  If I could both repair a simple, cheap, vacuum leak and sell you an
unneeded control unit for mega$$$ I might be tempted, too, especially if I
weren't hampered by a sense of ethics.  This is notably missing from many
service agencies.

Pull the ISV and clean it thoroughly several times with carb cleaner.
Replace it and see if there is improvement.  If improved, prepare to
replace the ISV.  ~$100 beats $375 + labor.

Your oxygen sensor may also be problematic.  Someone else more familiar
than I can suggest a testing procedure.  Again, a $50 OXS and a $9 socket
for the OXS beats $375.

Check for vacuum leaks as suggested below.

Which control unit?  The ECU?  Functional used ECUs are available.

Good luck.

At 09:00 AM 8/5/98 -0400, you wrote:
>As a follow up to my post yesterday (8/5), my 87 5K apparently has a bad
>control unit, which is responsible for the rough idling problem
>identified yesterday.  This part (I'm told) is manufactured only by VDO,
>as the car is a turbo, and the equivalent Bosch part can't be
>substituted.  As might be anticipated, dealer price is exorbitant
>(approx. $375 US).  Any suggestions as to parts sources or other ideas
>are much appreciated!
>Mark A. Trank
>87 5KCSTQ/150k and still going.......

To check for vacuum leaks:

1.	Let the car idle (if it will) and pull the oil dipstick.  If the engine dies (or falters severely) there is probably a leak.  (The system will compensate for some leakage but when the large added "leak" of the open dipstick hole is present it's too much leak for it to compensate for sufficiently.)  More modern cars are better able to handle leaks of this sort so you might have a seriously leaking system which still manage to pass this dipstick test.

2.	If a leak is indicated, with the engine idling, spray the various rubber parts both on the intake system and the pollution control stuff with ether based starting spray.  (You know, the stuff your grandfather sprayed down the carburetor [remember those?] of his old DeSoto on a -10F morning.)  When you spray the leaking region the rpms will pick up.  This will help indicate the area to search for the leak.

Caution!  Warning, Will Robinson!  Ether (also propane and butane) is extremely flammable.  Work outdoors away from sources of ignition.

Note: Some have used an unlit propane or butane torch in place of the ether.  Take your pick.  Either works.  Both are quite flammable.

3.	A very common spot for leaks to develop on turbo cars is the intercooler --> throttle body hose (looks like the "Michelin Tire Man").  Actually remove it and do a close inspection - particularly the bottom side where you can't see it when it's installed in the car.

4.	While this hose is off, feel the inside.  A coating of oil is normal but there should be no grit or small bits of metal.  If there is, you probably have troubles with the turbo itself.

5.	It is also entirely possible for a hose crack which causes a leak under boost to close up again when the system is under vacuum as it is at idle.  The most likely place for this is the same hose in point 3. above.  Removal and close inspection of that hose is suggested any time you suspect a possible vacuum leak.


*  Robert L. Myers  rmyers@inetone.net    Home 304-574-2372/1166  *
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*  '95 S6  Cashmere Grey                                          *