My accord would stumble on accelerating when cold so I figured at 180K the carbon build up was getting thick. I tried cleaning the throttle with spray tb cleaner but the idle started fluctuating up and down. The upper intake was pulled and the egr valve and passage was cleaned out. The throttle body was scrubbed as well as the IACV. The IACV was clearly dirty and the plate would barely move. When all was clean and reassembled the coolant was bled at the thermostat with the bleed valve. The car revs smoothly enough (no missing) but the idle races up and down from 1,000 up to 3,000 rpm. It is like someone mashing the gas (hard) every three seconds. I think I have a problem idle air control valve (IACV).

When I pull the air intake hose off and block the IACV port in the throttle body with my finger the surging takes place at a lower rpm. If I unplug the IACV electrical plug the same thing happens. If I unplug the TPS the engine idles at 3,000 rpm without the surging up and down. There are no CEL codes (until I pull the plug on the TPS of course).

I did try and let the car warm up without touching the gas to get the computer to relearn the idle. The strong up and down surging goes on even with the car in drive. I also used a Honda factory gasket on the throttle body as I have read the Fel-pro brand wont work. All the bolts were torqued to the 16 ft lbs required. It is not safe to drive it now. Any ideas out there? thanks,

98 accord in pain

 

here is a bit more data. I've tried checking for vacuum leaks around all the joints and hoses. No luck. I tried something different. I started the car and unplugged the Map sensor, TPS and IACV at the same time. I was surprised that it still ran. The surging up and down was at a much lower RPM. When I plug the IACV port in the throttle body with my thumb the idle smooths out at almost to normal level.

The throttle position censor shows .459 closed and 4.9 wide open. I've read about similar problems on the forum but not one with such a wide fluctuation in idle as I have. I hate to start throwing parts at this thing but I'm running out of options. Any ideas?

 

Can I ask what the color of the three wires to the tps are?

It does sound like a vac leak - I know you checked but the high - wide range it goes thru has me leaning towards that. The o-ring gasket for the IAC or aka the Rotary Air Control, was it replaced or anything added to help it seal.

 

Ah, you're thinking i mixed up the plugs. I checked that with the wiring diagram just to be sure. No dice. The o-ring gasket thingy on the idle air control was flat as a pancake so I shouldn't have reused it. Probably leaked. Anyway, I got a nice, new IACV and new gasket on so we'll see tomorrow. I dropped one of the nuts to the throttle body and it has fallen through a crack in the space-time continuum. So I gotta get a new one tomorrow. Wish me luck!

 

Here's luck seriously, 'cuz 2 sons have two old Hondas that do this idle oscillation and want to know how (you) solve it ...

 

Set your base idle and do the idle-re-learn procedure in this post.
https://www.hondaaccordforum.com/for...e-speed-38734/

 

Op- sorry for this.

UhOh - I think we've had this conversation before....for the 4th gens, clean and adjust the FITV, then clean the air boost valve.

 

Well, that finally did it. When I turned the key she fired right off and idled perfectly like there was never anything wrong! Turns out trying to clean the idle air control valve was a mistake. I cleaned the one on my other car with no trouble with the same throttle body cleaner (sensor safe). I just won't try that again without having a good replacement on hand in case of another failure.

It looks like you could take the electric actuator section apart from the rest by a couple of torx screws. Maybe you could isolate the more delicate portions and clean those with electronics cleaner instead. Food for thought. Thanks for the help ya'll.