Hi all, Wondering if I could get some help with this issue, I searched and searched and couldn't find any solution that worked. So here goes:

The car performs just fine when the engine is cold, but the more I drive it throughout the day and the warmer the engine gets, the worse the idle becomes (Starts off normal at around 700, then dips down to 500, then once it gets to 400 the power is halved). Also once the engine becomes hot enough for the cooling fans to kick on, the car will jolt and shutter. Any electrical load will make it worse. Battery, and alternator are still good though.

Engine: F22B1 VTEC

So far I've done:

-Checked for vacuum leaks with carb cleaner, couldn't find any
-Replaced air filter (August 2013)
-Replaced fuel filter
-Replaced radiator, thermostat, hoses, and bled cooling system
-Unplugged, checked, and cleaned IACV; seems to be working.
-Reset base idle as per the service manual to 550 RPM
-Checked for spark in all cylinders, pulled the wires to listen to idle change, all seem to be working
-Listened for fuel injectors clicking, all seem to be working.

Any ideas? I'm stumped.
Thanks in advance.

 

Have you checked for any stored codes?
There may be a code even if the CEL is not on.

 

I suppose it may have something to do with FITV. I am having same problem but my case is not very frequent. What happens is it comes and goes. Like if AC has kicked in,such power loss and rpm drops to 500 on idle. When i turn off and on car it goes. I am also in progress of diagnosing the problem. Its been 2 months and still going on.

 

The fitv will cause it to idle higher not lower. When's the last time you checked the air filter ? You should check the voltage with everything loaded up. It could be the alt going out.

 

Well seems legitimate. Can Alternator put soo much load........... what should be voltage with everything loaded up?

 

Good point. I have a feeling there may be, but I don't have an OBDII scan tool, I may be able to borrow one soon though. Will report any findings. Thanks

 

I haven't messed with the FITV yet, I thought that only if there are high idle, or hunting idle problems that is the go to source after checking vacuum leaks and cooling system bleeding. I forgot to mention that I replaced the air filter back in August 2013. Would a bad alt cause electrical load problems under idle? Or could the IACV really be bad? I thought it was supposed to compensate for electrical load by raising the idle.

 

I was thinking alternator going as well. not having a good charging system can wreak havoc on electrical systems. when motor is hot and idling, take a multimeter and test the battery with no load. no accessories on, nothing. . it should be 13.8-14.8volts. then load the engine. turn everything on high. observe the voltage . it should drop and come back up after the accessories have been turned on. if it drops below 13v the charging system if defective. with no accessories on. apply brakes. again voltage should not drop below 13v.. if the charging voltage doesn't distinctly change when you ran the tests then the VOLTAGE REGULATOR could be bad and is part of the alt and must be replaced.

 

Just posting an update, I had a hunch it may be the IACV still, and wanted to check the FITV anyway.

-I just took the throttle body off, cleaned it thoroughly with intake cleaner, opened the FITV, spun down the white housing and backed it off 1/4 turn. Reinstalled the plate.

-Replaced IACV with a used one from salvage yard, replaced gasket with new one.

-Reinstalled throttle body, hoses, and bled the cooling system.

Despite doing all this, the problem still persists, virtually no change... Perhaps there is a vacuum leak somewhere I haven't looked, any tips? Could it be a problem with engine mounts? I hear about these going bad alot on these 90's Hondas.

Until I can get access to a multi meter to check the Alternator, and OBDII scanner, nothing much else to do.

 

Well If you remove the air filter pipe you would see two hole sin throttle body. One top and other bottom. Theory says that when car gets warmed up and the fans kick in the hole below should not suck any air and the upper hole on blockage should turn the car off.

If that does not work take carb cleaner and spray at various possible areas to see if there is a leak. if there is a leak then the rpm would change.

 

both of those valves control air before the throttle plate. Iacv controls air flow depending on various sensors and/or parasitic engine load. fitv is only supposed to be open when cold. when hot it shuts. it depends on coolant temps.

if you had a vacuum leak after the throttle plate, your idle would be higher, not lower.

completely cap the vacuum line controlling the engine mount and see if that fixes your problem. if it doesn't, that is not the problem.

 

So if he is getting low idle this means that the air is blocking up somewhere (means not a vac leak). If it was a vac leak then it may be present even at when its cold.

I think two things highly possible culprit are
1. Alternator (Try removing the Alternator Plug for few seconds when car is idling low.Check the voltages with plug connected it should not be above specified range)
2. Or ECU his having trouble managing when it goes to closed loop from open loop