My car is a 1996 Civic w/ a D16Y5 engine. During idle, everything is fine when there is no load (750RPM). I guess I can say the same thing when there is load introduced i.e A/C. It gets to proper speed (810±50RPM) when the A/C is turned on. But here's the issue.

As soon as I press the A/C switch, it will increase the RPM right away (a hundred, that is the "Advanced signal" I guess), but after a second the RPM will dip a bit (maybe 200RPM less) and then after another 2 seconds it will seem to catch up to the ideal speed.

So to describe that better:

1.) No load - 750 RPM
2.) A/C on - 850 RPM (as soon as the switch is pressed)
3.) A/C on - 650 RPM (after a couple of seconds)
4.) A/C on - then stays around 800 RPM which is perfect

This cycle will repeat as the compressor cycles on/off.

However, a buddy said that the RPM shouldn't go down when the A/C is turned on as the IACV should be able to adjust the air intake based on the load introduced. He seems right based on what I've read on several posts.

What could be wrong with the system? Could the IACV be going bad? Maybe a leak somewhere causing the dip and then the ECU detects the fall in RPM and it will try to adjust, therefore causing the symptoms above?

Could it also be that the A/C is a bit overcharged and the initial 'burst' given by the IACV isn't sufficient thus causing the dip and the delayed adjustment of RPM?

Other loads doesn't seem to show the same issue but maybe it just goes unnoticeable their too light compared to the A/C.

 

Could a bad gasket in the IACV manifest the same symptoms? Since this is cheap I am planning to replace this first. But I have doubts because a worn gasket should cause a vacuum leak and that means high RPMs at idle.

If it's the IACV I can't get a brand new right now and will have to go to a junkyard.

 

Personally i would remove and clean out the IACV and FITV. Replace both the gaskets while your down there with gaskets from a Honda dealership. Make sure you properly set your idle and see if it helps. If it helps you just fixed it for next to free minus cost of gaskets and a can of carb cleaner.

With how easy these parts are to clean i see no reason to troubleshoot yet. Even if it didn't fix it consider it preventative maintenance.

 

Thanks for the advice. I regularly clean my IACV. I use WD40 though. Shouldn't hurt right? I don't have an FITV.

Anyone here who has a cross-sectional drawing of an IACV? Wanted to know the mechanism just so I can understand if the 2 second dip has anything to do with it. Like I said this is something that doesn't bother me too much, as the idle goes back up to normal after a couple of seconds. But if I can solve the issue cheap, why not.

 

WD-40 is a degreaser and water displacement product. (WD-40 Stands for water displacement 40th attempt). Being as coolant runs through the IACV and coolant is 50-60% water putting anything in the IACV that displaces water seams like a bad idea to me. (Like mixing oil and coolant it just doesn't work). Use carb or brake cleaner, it evaporates clean and wont contaminate your motor, just keep it off your seals.

Secondly if you clean it regularly and haven't changed that gasket, Change it. Especially if you got WD-40 on the gasket. As WD-40 is petroleum based and therefore eats rubber.



No exploded diagram sorry. Also not sure what you ment, but you should clean both holes.... That what she said.... \/




ALSO: its normal for your idle to change a bit when putting load on the system. (ex. putting down windows, turning on A/C, turning the wheel while standing still.) Though it should even out after a second.

 

I have same problem cleaned out IACV, and replaced the rubber gasket in it. No difference... Idk could just be normal.

 

I use WD40 to clean the insides of the IACV. I don't have the part where coolant passes around the IACV frame. That's only for cold weather, afterall. It's useless in a tropical country like the Philippines.

 

Man, could be an ECU thing then. What year is yours? I heard there are 3 versions of ECU for the 1996-2000 Civic. Maybe it's how it is programmed?

 

It's a 93. Yeah the hx, dx, ex, and si trims all run a different ecu for 96-00. Don't think it's a ecu problem, but wouldn't rule it out due to age. I been told because the electrical system is so "old" and "puny" that it's not gonna take the load like it did new from factory. Especially if you have aftermarket deck, hids, or subs. If it returns to original idle, with the accessories on I would leave it alone.... I'm used to it on my sol lol.

 

Didn't see you were from the Philippians. I am in the North Eastern US so i am in a foot of snow right now and never even took that into consideration.


Also I have read different country's have different ECU's on an otherwise identical model vehicle. Simply to account for altitude and things like that. So the same ECU will perform differently depending on where you are in the world.

 

I had my A/C recharged to the minimum acceptable pressure levels at 1500RPM then had my idle reset, guess what.. RPM no longer dips at idle when A/C is turned on. I guess before it's just too much load than the ECU expects, so it had to play catch up for a bit.

 

We could use a little snow over here. 100-70% humidity all year makes our A/C work harder. The puny radiator and condenser doesn't help either. I guess Civics aren't designed for this environment but the irony is we're right beneath Japan.

 

WD-40 isn't an effective cleaner, it's oil based lubricant and is why it displaces water. I heard once it's main ingredient is fish oil.

Brake Cleaner is your better bet at cleaning the insides of the IACV. WD-40 is going to leave an oil residue which will just attract dirt unlike a clean residue free cleaning with brake cleaner.

I'd actually avoid carb cleaner too as it's a pretty harsh solvent and the IACV might have delicate plastics in it or special plating finishes. I know the 92-95 FITV has a plastic bellow in it. Never actually ripped open an IACV to see the guts.

Non-chlorinated brake cleaner is your friend and won't leave a dirt magnet residue like WD-40. Also it will dislodge a lot more carbon over the WD-40.

 

Makes sense. Will use brake cleaner with the IACV from now on. Thanks.