Racer X
SHO Pilot, Retired
This has been a bit of an issue for a while, but lately it has gotten much worse.
I've had this issue since I bought the car in 2004. If I started the A/C (or any mode that made use of the compressor), everything would be ok for the most part, save for the interesting drivablity issues that come with running the A/C and driving at low speed (which I've recently found to be a common SHO thing). Once I turned off the A/C after letting it run for a short while, the idle speed would jump up to 1200 - 1300 RPM... and just hang there. Once the fan shuts off after a few minutes, the idle would start to come down, bounce back up a little, come down some more, bounce up again, and so on. Eventually, it would settle down to almost normal. If I wanted to stop the behavior, all that was necessary was to stop and restart the engine. After that, everything would be normal until I cycled the A/C on and off again.
After the convention, I noticed that more and more, my idle was a bit ******, generally erring on the side of being too high. I figured, hey, maybe I ran too hard during the track day, and the computer has some weird ideas as to what normal is. So I fell back on my IT training, and made use of a tried and true adage:
When in doubt, plug it out.
After the KAM was cleared, I reconnected the Batt (-), and reset the idle per the generally accepted procedure. And then I noticed something else weird. As I was turning on accessories, the idle was jumping slightly and falling back to normal. I hit the headlights first, and then the A/C max, then the rear defroster. I cut the A/C and the idle went high... par for the course. I cut the lights and rear defroster, and it came down? WTF?
Rear def on, idle goes high again. Turn it off, and the idle falls. When the fan finally stopped, so did this behavior.
Later on, I noticed while driving that if the headlights were on and the cooling fan came on, the idle went high. Cut the lights while the fan is still on, and the idle goes normal again. Fan stops with the lights on, and idle goes normal.
This is just ridiculous.
Another odd thing I've noticed... when triggered by the engine temp, the fan won't just come on. It'll twitch, just for a fraction of a second, then wait... then twitch again... then wait... then come on.
I've watched the voltage during all these events, and the readings remained well over 13.6v (though that's questionable, as I'm beginning to have my doubts on the readings from my 30 year old Fluke DMM).
So, where do I look next? I'm not one for blindly replacing parts, but I will troubleshoot like a ****. That, and I want to fix this before it becomes a bigger issue (like most things left neglected on any SHO).
So, thoughts?
Thanks all.
I've had this issue since I bought the car in 2004. If I started the A/C (or any mode that made use of the compressor), everything would be ok for the most part, save for the interesting drivablity issues that come with running the A/C and driving at low speed (which I've recently found to be a common SHO thing). Once I turned off the A/C after letting it run for a short while, the idle speed would jump up to 1200 - 1300 RPM... and just hang there. Once the fan shuts off after a few minutes, the idle would start to come down, bounce back up a little, come down some more, bounce up again, and so on. Eventually, it would settle down to almost normal. If I wanted to stop the behavior, all that was necessary was to stop and restart the engine. After that, everything would be normal until I cycled the A/C on and off again.
After the convention, I noticed that more and more, my idle was a bit ******, generally erring on the side of being too high. I figured, hey, maybe I ran too hard during the track day, and the computer has some weird ideas as to what normal is. So I fell back on my IT training, and made use of a tried and true adage:
When in doubt, plug it out.
After the KAM was cleared, I reconnected the Batt (-), and reset the idle per the generally accepted procedure. And then I noticed something else weird. As I was turning on accessories, the idle was jumping slightly and falling back to normal. I hit the headlights first, and then the A/C max, then the rear defroster. I cut the A/C and the idle went high... par for the course. I cut the lights and rear defroster, and it came down? WTF?
Rear def on, idle goes high again. Turn it off, and the idle falls. When the fan finally stopped, so did this behavior.
Later on, I noticed while driving that if the headlights were on and the cooling fan came on, the idle went high. Cut the lights while the fan is still on, and the idle goes normal again. Fan stops with the lights on, and idle goes normal.
This is just ridiculous.
Another odd thing I've noticed... when triggered by the engine temp, the fan won't just come on. It'll twitch, just for a fraction of a second, then wait... then twitch again... then wait... then come on.
I've watched the voltage during all these events, and the readings remained well over 13.6v (though that's questionable, as I'm beginning to have my doubts on the readings from my 30 year old Fluke DMM).
So, where do I look next? I'm not one for blindly replacing parts, but I will troubleshoot like a ****. That, and I want to fix this before it becomes a bigger issue (like most things left neglected on any SHO).
So, thoughts?
Thanks all.
