Surging at idle hot/cold - '87 S4 AUTO
04-17-2014, 01:35 PM
#1
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Surging at idle hot/cold - '87 S4 AUTO
Friends,
I parked her last night and this morning she is surging 850-950 over and over - annoying. and will stall if I don't feather the gas from a start. Holding down on the brake seems to attenuate this and it settles at 950 with slight surging.
Over the last 6 months I've:
replaced the O2 sensor and temp II.
I re-seated the temp II sensor with no change. I just don't understand what happened between shutting her off last night and starting her up today. She just has a hunting idle; if I get up to speed no problem.
What the heck is going on here?
I parked her last night and this morning she is surging 850-950 over and over - annoying. and will stall if I don't feather the gas from a start. Holding down on the brake seems to attenuate this and it settles at 950 with slight surging.
Over the last 6 months I've:
replaced the O2 sensor and temp II.
I re-seated the temp II sensor with no change. I just don't understand what happened between shutting her off last night and starting her up today. She just has a hunting idle; if I get up to speed no problem.
What the heck is going on here?
04-17-2014, 02:57 PM
#2
Mine did the same thing until I replaced the O2 sensor. After that, it never a surged again. Is your new O2 sensor the splice in unit or the whole new harness unit?
The reason I'm asking is that you really need to screw in the sensor before you splice the wire. That way there is no torque on the splice from the installation which could cause a loose or broke connection.
Of course it could be a myriad of other things causing your surge, so good luck!
The reason I'm asking is that you really need to screw in the sensor before you splice the wire. That way there is no torque on the splice from the installation which could cause a loose or broke connection.
Of course it could be a myriad of other things causing your surge, so good luck!
04-18-2014, 02:13 AM
#4
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sticky idle stabilizer valve.... Your idle is computer controlled it opens and closes a bypass valve to hold the idle compensates when you turn on the A/C or put it in gear. Not an unusual problem at all.
04-18-2014, 09:08 AM
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Here's what I'll try later today:
"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"
"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"
04-18-2014, 09:14 AM
#7
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Yes.
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04-19-2014, 06:22 AM
#8
Racer
hi,
press the gas pedal just a tiny bit to release the idle switch at the intake valve. When the switch is open, the idle actuator / stabilizer is not active. If you still have problems you need to look further for a cause. Disconnect the lambda (O2) sensor. That makes the LH think the O2 sensor is not ready yet and run a fixed program ignoring any O2 sensor readings. That may rule out a faulty O2 sensor.
A sticky idle actuator is quite common. Sometimes it helps to spray some WD40 into the suction side of the actuator to help clean things up and lubricate. Here is a link with some extra info:
http://jenniskens.livedsl.nl/Technic...0/MyTip078.htm
regards
Theo
1992 928 GTS
press the gas pedal just a tiny bit to release the idle switch at the intake valve. When the switch is open, the idle actuator / stabilizer is not active. If you still have problems you need to look further for a cause. Disconnect the lambda (O2) sensor. That makes the LH think the O2 sensor is not ready yet and run a fixed program ignoring any O2 sensor readings. That may rule out a faulty O2 sensor.
A sticky idle actuator is quite common. Sometimes it helps to spray some WD40 into the suction side of the actuator to help clean things up and lubricate. Here is a link with some extra info:
http://jenniskens.livedsl.nl/Technic...0/MyTip078.htm
regards
Theo
1992 928 GTS