GimpyCivic

This is one of the MOST common problems with Hondas (no ----). Its one of 6 things:

1.) Base ignition timing too high
2.) Vacuum leak
3.) Idle air screw set too high
4.) FIV bad (stuck open)
5.) IACV/EACV (whatever you wanna call it) bad or clogged with ----.
6.) Older Accord/Prelude: the AIB (Start Air Boost) check valve on the drivers side of the Intake mani can get stuck open, just remove it.. it does jackshit anyway.

With the car warmed up to operating temperature: I start by jumping the service connector and pulling the IACV connector. I then set the base ignition timing and base idle (650rpm is where i try to get it with my external tach). I then shutoff the car, unjump the service connector, plug the IACV back in and reset the ECU via the backup fuse for 15-20 seconds. Restart. If its still jumping around I start looking for vacuum leaks. If I can't find any I swap on a spare FIV (I keep these things around ... I don't run one anymore, but my friends do) and that is usually the end of the troubleshooting session. Rarely do I see an bad IACV.. and you hope not to, because unless you have a hookup at a scrapyard they're like 150-250 depending on the model of the car. The last resort is to try and clean out the ports of the IACV and see if that gets you anywhere....

In my experience fixing this on probobly 20-30 honda's its been timing, idle air screw and vacuum leak that usually is the cause. Thankfully the cheap ----

The way honda idles their cars when an environmental problem like timing etc is wrong its cycling the IACV causing the updownupdownupdown idle... very annoying. Sometime if you're in traffic notice how many Hondas do it! Tons of them.

88crxSi

thats just the thing. mine doesnt idle up, it stumbles DOWN.. never over 600rpm at full operating temp.

idle, no elec load 600 rpm.
the fan kicks in cuz temps get up, idle drops to 400rpm and runs like ***... tough to describe the sound..

ShadowRex

4.) FIV bad (stuck open)


whats that Yea the worst i seen on a idle being messed up ws a ecu a fast swap solved the problem thats VERY RARE that the ecu screws up like that though..

Most I have done is Idle screw and clogged *** IACV where i am at people reuse evrything from friend to friend. Its a wonder how some of these parts make there way around lol. checked a few timings on them but i like yer mini write up.

Sticky Maybe?

GimpyCivic

I would wager your IACV is bad... unplug it and see if the car acts the same. It'll toss a CEL but if it acts the same the IACV isnt doin anything. As you know it will kick up idle a bit for AC, highload electrical conditions and other things.

GimpyCivic

This diagram sucks, but see #13? under the TB? That whole the large dingus is the FIV. Fast Idle Valve. It has a thermo-wax plug that when cold.. opens and allows more air into the intake tract to warm the car up quicker/help cold idle. As coolant temp rises the wax expands and closes it. What happens is over time the wax plug gets messed up and it sticks open or closed.. usually open unfortunatly and it plays hell with the idle... especially warm idle since the ECU is then in closed loop operation.

Some FIV's are on the bottom/side of the TB.. some are on the intake manifold itself. It just depends on the year/make of the Honda.

As you can see above I keep 2-3 of these on hand at all times... kinda like igniters and OBD0 distribs :P

88crxSi

does the ecu read the o2 at full warm idle.. ?

GimpyCivic

the only time it doesnt read the o2 is WOT and cold idle/warmup. at those times it relies soley on the 2d timing/fuel map.

88crxSi

would a bad o2 cause crapy idle? my last emmiosions test was right on the limits of pass/fail. if that helps

GimpyCivic

I guess anything possible... heh as they get old they don't go bad so much as they lose sensitivity. Do you have a spare to try?

88crxSi

no spare. I just recently got the courage to do anything in the engine bay w/ my car.. interior and electronics are no prob.. next step is under the hood...