928S4 Idle/Run Issue Driving Me Nuts!!--A Fix!!
10-17-2016, 09:56 PM
#1
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928S4 Idle/Run Issue Driving Me Nuts!!--A Fix!!
See this thread for the details of what I'd changed: https://rennlist.com/forums/928-foru...g-me-nuts.html
After still having an unstable idle/stalling and a miss below 3,000 RPM, I decided to try a different EZK computer, so I purchased a used one from DC Automotive. When I installed it, the miss was gone and idle was much better, although still a bit unstable. Putting the original one back in resulted in the symptoms returning. Seems the EZK box was part of the problem! I'd already sent a spare MAF out to Louis Ott for checking (it was marginal, so I got a re-calibrated unit from him). I also bought a new idle stabilizer valve from Roger Tyson. I installed those units a couple of days ago, but still have a hunting idle, but only when in gear with the A/C engaged... I noticed that the electrical voltage would fluctuate as the alternator seemed to drop out right at idle speed, which would lower the power to the idle valve, causing the engine to drop below desired idle. The LH computer would increase the duty cycle to the idle valve, raising the idle speed, which would cause the alternator to come back on line, raising the voltage to 14, making the idle valve work better and the idle speed would go high, starting the process all over. I discovered that turning the A/C off kept the voltage above 13 at idle and it idled rock solid. Or, if the A/C was on AND I turned the headlights on, the voltage would drop to 12 and become stable. Interesting! I installed a rebuilt alternator that I had, but it still acts the same way. Might be time for an alternator upgrade????
After still having an unstable idle/stalling and a miss below 3,000 RPM, I decided to try a different EZK computer, so I purchased a used one from DC Automotive. When I installed it, the miss was gone and idle was much better, although still a bit unstable. Putting the original one back in resulted in the symptoms returning. Seems the EZK box was part of the problem! I'd already sent a spare MAF out to Louis Ott for checking (it was marginal, so I got a re-calibrated unit from him). I also bought a new idle stabilizer valve from Roger Tyson. I installed those units a couple of days ago, but still have a hunting idle, but only when in gear with the A/C engaged... I noticed that the electrical voltage would fluctuate as the alternator seemed to drop out right at idle speed, which would lower the power to the idle valve, causing the engine to drop below desired idle. The LH computer would increase the duty cycle to the idle valve, raising the idle speed, which would cause the alternator to come back on line, raising the voltage to 14, making the idle valve work better and the idle speed would go high, starting the process all over. I discovered that turning the A/C off kept the voltage above 13 at idle and it idled rock solid. Or, if the A/C was on AND I turned the headlights on, the voltage would drop to 12 and become stable. Interesting! I installed a rebuilt alternator that I had, but it still acts the same way. Might be time for an alternator upgrade????
10-18-2016, 06:44 AM
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Considering I have had interesting idle symptoms that no one has been able to diagnose, this is interesting information. Maybe the EZK boxes are finally starting to go out on these cars.
10-18-2016, 07:20 AM
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When I got my 91 S4 in 2000, it had a lumpy idle. It sounded as it would randomly skip firing cylinders. Really annoying!
It had already gotten a new timing belt and water pump before I drove it home. We had the injectors cleaned, replaced all ignition parts (wires, rotors, caps, plugs), checked the MAF, plugged-in a different LH, did a complete intake job with new idle stabilizer, knock sensors and TPS (the only part that was obviously broken). Still, the idle would not change.
Then DEVEK performed a Rislone treatment and did an oil change. I suspect there may have been an Italian tune-up somewhere before the oil change as well, but that wasn't listed on the invoice. Whatever they did - it totally transformed the engine. Since then, the car idles "smooth as buttah".
Sometimes an annoying problem only needs a cheap and simple solution.
It had already gotten a new timing belt and water pump before I drove it home. We had the injectors cleaned, replaced all ignition parts (wires, rotors, caps, plugs), checked the MAF, plugged-in a different LH, did a complete intake job with new idle stabilizer, knock sensors and TPS (the only part that was obviously broken). Still, the idle would not change.
Then DEVEK performed a Rislone treatment and did an oil change. I suspect there may have been an Italian tune-up somewhere before the oil change as well, but that wasn't listed on the invoice. Whatever they did - it totally transformed the engine. Since then, the car idles "smooth as buttah".
Sometimes an annoying problem only needs a cheap and simple solution.