MountainBiker Posted May 4, 2006 Share Posted May 4, 2006 Besides the Air Conditioner? I know that when the A/C pump is on, the engine "idle up" function is used, but there is something else that is triggering it, because it happens even with the A/C off. If you are on a super steep road (think San Francisco, but longer distances on dirt or gravel surfaces), and using a low gear to control the speed, every so often, the engine backpressure decreases, causing an increase in speed! I'm pretty certain this is the "idle up" function in the ECM. I can easily turn off the A/C on these steep decents, but something else is causing it, so I'd like to disable it with a switch. This can be a bit scary when on loose gravel roads, since you speed up when the "idle up" occurs, so you hit the brakes, and ABS engages, while continuing to speed up! ABS disabling on gravel is an additional subject, not in the scope of this thread. Quote Link to comment Share on other sites More sharing options...
Legacy777 Posted May 4, 2006 Share Posted May 4, 2006 What year and model?? The a/c compressor can be on when the HVAC system is on Defrost or Defrost/heat, as well as A/C Quote Link to comment Share on other sites More sharing options...
boxerhummfetish Posted May 5, 2006 Share Posted May 5, 2006 alternator? lights off and a trickle charger could both maybe minimize that from happening. new batt helps too. Quote Link to comment Share on other sites More sharing options...
keltik Posted May 5, 2006 Share Posted May 5, 2006 My wagon does this frequently but i suspect its the Auto box equalising things to stop the torque converter stalling. If yours is a manual i'd still be interested in hearing a pro opinion. KELTIK Quote Link to comment Share on other sites More sharing options...
cookie Posted May 5, 2006 Share Posted May 5, 2006 My 5 speed does this a little bit to cut emissions I believe. When you chop the throttle it causes unburnt gas to dump. It raises the idle a bit and take a moment to come down to prevent this. My ECU is always thinking while I'm just listening to the stereo. Between the electrical load changes, emissions stuff, and AC an automatic is often worse in this regard. Quote Link to comment Share on other sites More sharing options...
Lawsonmh15 Posted May 5, 2006 Share Posted May 5, 2006 Idle Air Control Valve. Quote Link to comment Share on other sites More sharing options...
MountainBiker Posted May 5, 2006 Author Share Posted May 5, 2006 Model and year are in my sig. '02 Forester, so it doesn't have the automatic activation during defrost as some other models/years do. alternator? lights off and a trickle charger could both maybe minimize that from happening. new batt helps too. The battery is in really good shape, and is about 3 months old. But a possibility is that the alternator loading may occassionally call for the "idle up" My wagon does this frequently but i suspect its the Auto box equalising things to stop the torque converter stalling. It's a 4EAT. And the trans control unit might be doing some funny things. Idle Air Control Valve. Yes, this is the likely culprit! However, it is controlled completely by the ECM on my '02 Forester and it is also used to control the normal idle speed. When this problem occurs, I am usually at 1500-3000 rpm, so I need to figure out what input is causing the ECM to bump the air volume in an effort to increase the idle speed. Obviously, at that rev range, I don't need an increase, but the ECM seems to think I do. I expect this idle up phenomena is just a normal occurence, but I want to disable it. Of course it could also be a symptom of something malfunctioning on my car, but I doubt it. Quote Link to comment Share on other sites More sharing options...
cookie Posted May 5, 2006 Share Posted May 5, 2006 I see you are up in Sonoma. I was thinking you might try my car if you are ever donw San Mateo way and see if it works about the same. If your car is doing what it is supposed to and you disable you might flunk smog if you have it. Quote Link to comment Share on other sites More sharing options...
Legacy777 Posted May 5, 2006 Share Posted May 5, 2006 Model and year are in my sig. '02 Forester, so it doesn't have the automatic activation during defrost as some other models/years do. I'd still be suspicious if the A/C compressor doesn't come when you have the HVAC system in defrost. Have you put the HVAC system on defrost, opened the hood, and looked to see if the a/c compressor is clutch is engaged? What setting do you normally have the HVAC on when you notice the problem? Quote Link to comment Share on other sites More sharing options...
MountainBiker Posted May 5, 2006 Author Share Posted May 5, 2006 I see you are up in Sonoma. I was thinking you might try my car if you are ever donw San Mateo way and see if it works about the same. If your car is doing what it is supposed to and you disable you might flunk smog if you have it. Thanks for the offer, but I have a couple Forester friends around here. Assuming it is working as it is supposed to, I would only disable it temporarily. The only time this comes up as an issue is when I'm offroading. Quote Link to comment Share on other sites More sharing options...
MountainBiker Posted May 5, 2006 Author Share Posted May 5, 2006 I'd still be suspicious if the A/C compressor doesn't come when you have the HVAC system in defrost. Have you put the HVAC system on defrost, opened the hood, and looked to see if the a/c compressor is clutch is engaged? What setting do you normally have the HVAC on when you notice the problem? I see where you are coming from. My Toyota does this, and I hate it! The Forester doesn't operate the compressor enough to engage the fan when in defrost mode and the AC button is off. As far as I know, if the AC compressor is on, the radiator fan is on at the same time, 100% of the time. But I will do as you suggest, and see if the AC clutch is engaging occassionally. However, I rarely have the HVAC in a mode where it is blowing air on the windshield, because that tends to dry out my eyes, since I'm tall, and the air blow right onto my face. Quote Link to comment Share on other sites More sharing options...
Setright Posted May 6, 2006 Share Posted May 6, 2006 Moving the control to defrost will switch on the AC, but if you hit the AC button afterwards the compressor is switched off again. Quote Link to comment Share on other sites More sharing options...
MountainBiker Posted May 7, 2006 Author Share Posted May 7, 2006 Moving the control to defrost will switch on the AC, but if you hit the AC button afterwards the compressor is switched off again. Once again, this is not the case on my '02 Forester. The only way AC compressor comes on, is if I physically push the AC button. BTW, the service manual lists the following for what will trigger an "idle up" condition: -Alternator load rising to some threshold value (not stated) -AC compressor being on Quote Link to comment Share on other sites More sharing options...
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