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Hey guys, I’ve got a 97 Civic LX that’s giving me a little trouble. On hot days, especially while highway driving the air from the A/C will suddenly get warm and the car will idle at 1500. This usually lasts maybe five minutes, then the car will lurch from the compressor kicking on and idle will go to around 400. So when air is warm…high idle. When air is cold…low idle. The idle isn’t consistent even with the A/C off, sometimes it seems too low especially when there’s an electrical load on the system. Sometimes it’s at 900. Before all this started it stayed at a steady 650 (approx).
These are the parts I’ve thrown in it recently, not just because of this problem but for maintenance and other reasons: New ignition coil, new NGK plugs, new distributor cap and rotor, new battery, new fuel filter. I got my alternator tested and all was good there including voltage regulator.
Could this be caused by a bad AC belt? Basically I’m wondering how the computer knows to increase idle to compensate for AC being on? Does it know from you pressing the AC button, or does it know when it sees the idle begin to increase? Not sure if that makes any sense, let me know if it doesn’t.
Thanks,
TheFinderP.S. I’m going to replace the drive belts soon because
they do seem somewhat old. Maybe that will fix?
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OK… Lots of A/C questions today…
When you turn on your A/C the engine needs to run at a faster idle due to the increased load put on the engine by the compressor… The radiator requires more cooling, that is why there is an extra fan near your radiator. The ECU gets told that your A/C is on and makes the necessary changes for the engine (increase RPMS, turn on fan, engage Compressor clutch)
Here goes my assessment based upon what you have told me…
The idle going up is what it is supposed to do, right, but is your compressor clutch kicking on at 1500? I would say probably not… Hence why you do not have cold air… You tell me…. The ECU thinks the compressor is running so it still increases the idle…
I believe you may be having an issue with your compressor/clutch… Get a manifold and hook it up to your A/C unit. For outside ambient air temperatures between 70-95 the reading should be 35 to 50 psi respectively. The high side should be somewhere around 2.2 to 2.5 X the ambient air temperature. So on a 70 degree day your low should read around 35 and the high should read 155 to 175.
The idle being wrong when there is no load is something that may be a completely different issue… perhaps something mechanical…
I would rule out the Compressor first if you are interested in keeping your A/C and see what your idle is..
You may also try temporarily removing your belts and see how your engine runs….
-Karl
here is a link for solving honda idle problems.
I would suspect the IAC. The IAC is what controls
idle speed when ac or a load device is used.https://www.ericthecarguy.com/faq/solving-automotive-idle-problems
I think you might have two unrelated problems. I would check the idle problem like college man suggested and then check out the A/C.
Thanks everyone for the advice! I have suspected the IACV, but it’s a pricey part and so far I’m not aware of a way to test whether or not it’s actually the problem without replacing it. I’d like a set of manifold gauges anyway so I guess this is my excuse to get some.
As far as the coil is concerned, the old coil was kaput so I can’t throw that one back in to see if it helps. I didn’t have the money for drive belts today but I did tighten the AC belt to see if that would help at all because (I failed to mention this important fact) the AC belt does squeal some times. It’s been doing that since I got it and these problems just cropped up. I will know tomorrow if tightening the belt helped at all.
So is there a way to test the IACV without getting another one?
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