Idle Stabilizer Diagnostic / Temporary Fix

Idle Stabilizer Diagnostic / Temporary Fix

>My shark idles at around 5-650RPM and at times is very rough. It
>always seems to threaten to drop off to nothing but doesn't. Also, on
>rare occasions at a stoplight the idle will jump to 11-1200RPM. I am
>beginning to suspect the injectors.
>Any help?

Maybe it's to do with the idle regulator under the front of the intake. Learned a trick from Kevin Jackson who had surging and after clutching from a high rev the idle dipped enough to stall. Procedure that diagnosed the idle regulator (problem only cured for a while, it turned out that a new regulator was needed):

Take off the air box top and bottom and air mass sensor

Looking into large elbow there is a big vacuum hose exit to the car's left. This splits into a line to the idle stabiliser and to the intake

Feed a capillary tube, about 40 cm, in the line going to the front. This vacuum line branch goes under the intake to the idle regulator. Spray wd-40 into the tube a few times and blow it forth (mouth power). Take out the tube, put everything together and let soak in during the night.

The next morning my idle was stable, smooth and no more dip. It lasted for quite a few weeks.

Math Creemers
87 5sp

[Here's a quicker method, but it may not be as effictive:]

Next to the throttle linkage is a 3-way splitter - one line runs to the brake booster, one into the side of the intake, and one down under the intake at the rear. Undo the hose going down under the intake at the rear and spray a bunch of the WD-40 in there (engine off - I guess you could run the engine but I didn't try it that way). This hose feeds in just ahead of the throttle body and with a little luck the WD-40 will be pulled in/around/through the idle stabilizer and give it a lube. But given the heat, this is reportedly a temporary fix (maybe 2 weeks) but does help you localize the problem. You'll get some funny exhaust smell when the engine burns the WD-40.

John Pirtle
87 a/t 125k

John, et al, I used what I feel to be a better penetrating oil for my idle stabilizer problem. I've been using "Kroil" in the aviation industry for years, and it is far superior to WD-40. Also, I helped it along the path down the tube with low pressure compressed air. Did it a second time a few hours later, and let the car sit overnight. The next morning the car started and idled great. Still idling great, but we'll see how long it lasts. I still plan to try Wally's procedure of turning off, and restarting the car while driving @ 45mph. Good luck to us all,

Chris lockhart
'89 928GT

I found this website for Kroil, the penetrating oil that Chris said works so well and thought I'd pass it on:

$8 plus shipping for a 13oz aerosol can.

Jim Morehouse
Allentown, PA
'82 928

The unit in question, which goes by a number of aliases (idle stabilizer, rotary idle actuator, idle speed actuator), is the ECU-controlled servo that controls the idle speed on S4 - up cars. It does this by regulating the flow of air from a fitting before the throttle to a fitting on the intake manifold after the throttle. Thus, the idle actuator or idle stabilizer acts as a computer-controlled bypass valve around the throttle,
controlling the idle speed. The actuator valve sometimes begins to stick due to crud build-up.

The clearest illustration is on page 24-216 in the shop manual. There is a fitting in the side of the large tube that connects the MAF sensor to the throttle body. Air that flows from this fitting thus has passed thru the MAF sensor (and is "measured air"), but has not passed thru the throttle (and is not "controlled air"). There is a Tee in the air hose attached to this fitting. One leg of the Tee runs to the inlet side of the idle
actuator, furnishing the bypass air to control the idle speed. The other leg of the Tee runs to the vacuum ejector, the slant-Tee vacuum fitting located on the right side of the intake, near the throttle cable quadrant. (This fitting is a vacuum booster, utilizing air flow from the Tee and large inlet tube into the intake manifold to furnish boosted vacuum to the vacuum brake booster.)

There are three lines on this slant-Tee fitting. One runs to the vacuum brake booster; one runs to the intake manifold plenum; and one runs under the manifold. If you disconnect the input tube (the one that runs under the manifold to the Tee) and block the opening in the fitting, then spray a solvent, such as WD40, into the tube running under the manifold, the air flow into the idle actuator will carry some of the solvent into the valve section of the actuator, where it may or may not remove some of the crud and reduce the sticking.

If you are desperate enough, you can pull the air filter housing and MAF sensor off, clamp the inlet hose shut at the slant-Tee, and spray solvent into the fitting in the large inlet tube with the engine idling. This will get a heavier dosage of solvent to the idle actuator valve mechanism.

Wally Plumley
928 Specialists

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