I have a 1991 Honda Accored EX with 393,000 KM's. It is 5 speed fuel injected. Anyways it idles at 1500, it doesn't surge, doesn't do anythign once it warms up, just stays there. I was told to turn downt he idle by some people but was wondering whatt eh problem would be caused by, could it be somehting i dirty or a vacum leak? if so where would it be and is the idle screw?




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IACV stuck open? The IACV is a rectangularish alloy boxy thing on the front of the plenum chamber, it has an electrical connetion attached to it's front and a couple of small diameter rubber coolant hoses underneath. Take this off (two bolts, easy to access, but you can probably leave the connector and hoses in place for now) and plug the two holes you'll see in the plenum chamber (plug them properly, get a friend to hold their thumbs over the holes, or whatever, but don't let anything get sucked in!), and start the engine.

If the idle is now much lower (possibly too low if it's changed) then the IACV is probablystuck open, the IACV gasket is suspect (it's a rubber gasket, you'll see it on the IACV), or the ECU is telling it to be more open than it should be. Now thoroughly spray the guts of the IACV with throttle body cleaner and refit it. If the idle is now OK then the IACV was just stuck open. If the idle is still high then it could be that cleaning the IACV didn't fix it, or maybe it's the gasket which should be replaced (but you can try some gasket goo to seal it up,usenon hardening gasket sealant such as Permatex Aviation Gasket No3 or similar, not silicone). If it still no good then it could be a sensor problem resulting in the ECU telling the IACV to do the wrong thing.

 

ok i removed it and had the holes plugged. When i first started it it was at 1200 rpm's but after 25 seconds had worked its way down to 750 and held there. So I'm going to clean it and see if that fixes it or replace the gasket thanks

 

wait....so you plugged both holes in the intake and the engine didn't stall? that means you have a vacuum leak. and it's VERY steady leak too.

it can also be carbon buildup on the throttle plate or a misadjusted base idle screw. typcially honda throtte body gaskets do not crack or leak.

 

750rpmis the correct idle speed (650rpm to 750 rpm), and is also is more or less the correct idle speed with no auxilliary loads and the IACV disconnected, i.e. if you put the car in 'diagnostic' mode (i.e. shorting the blue connector under the dash will cause the IACV to shut off) the 'base' idle should be adjustedto 650 to 750rpm. But, if you then turn on say the air-con (still in 'diagnostic') the idle will drop way down because the IACV isn't operating. This suggests that the base idle is correctly set, and that you have no air leaks not associated with the IACV, unless perhaps the there is an air leak and the butterfly is adjusted completely closed (or nearly) to account for it (i.e. a bodge adjustment of the butterfly valve to make up for a slight leak somewhere else), but my bet is that there isn't an air leak.

If you block the IACV ports and the idle is now correct whereas before with the IACV active it was high then this suggests the IACV is stuck open or the rubber gasket is suspect. However, the fact that it now starts at 1200rpm and then drops to 750 isn't what I'd expect with the IACV ports blocked (it ought to just idle low or at the correct idle with no change, until perhaps the engine temp increases).

Perhaps the port(s) wasn't properly blocked off initially but vacuum then sealed it after the 25 seconds?? Or, perhaps the butterfly was not quite closed (to the idle position, i.e. very slightly cracked open a bit too far) but then closed up with vibration etc?? If it's this then try cleaning the throttle body, you may have gunk causing the problem at this point, or at least contributing to it. Don't just clean it, lubricate the butterfly shaft bushes as well.

 

base idle speed should be 550rpm(+/-50rpm)
a sudden cut off of both ports should stall the engine in my experience.

 

Well I cleaned it, and now it idles at 600, but when i give it gas and let off it almost stalls, or if i move the steering wheel or put any other load on it, then it recovers before stalling and idles correctly, what happened?

 

Well it may have been dirt or something but i let it run for 30 minutes and pulled the ecu fuse to reset it, and it seems to be fine now. Must have just been some gunk that came lose, the car has 400,000 on it so there was quite a bit of buildup

 

400,000 miles?? small detail left out... [8D]

 

very virst post i have that detail lol. its 393,000 km's or 244,198 miles