A mechanic told me that the Idle Air Control Valve on a 93 EX can be bypassed. Is this true, and has anyone here done this?

 

I would immediately turn 180 degrees from this guy and run as fast as you can.
Sure you could disable it, but unless you don't mind having to constantly have you foot on the accelerator, have the Check Engine Lamp glaring at you and failing the inspection emissions test; I wouldn't advise it.

P

 

yeah, besides that, its all you. haha. P is right though. terrible terrible idea. there are some systems you can delete or bypass, like the cat for example, but some stuff need just be left alone. lets call these one of those.

 

well this proves my theory that this particular mechanic is totally inept. i had my doubts about him already, due to previous f*ckups. i won't be visiting his shop anymore.

 

Here's my problem:
now that it's starting to cool off (in florida), this is when the problems start.
when it's warm outside (most of the year) nothing happens, but as soon as the temperature outside drops below 65 degrees. once the engine has been running for a few minutes, the engine starts surging while driving. when idling in park or neutral, the rpm gauge jumps between 1300 and 2000, but if i'm at a complete stop in d4 it does not idle erratically, only when in P or N, like when i'm in a drive-thru bank teller or fast food place. the colder it gets outside, the worse it gets. the mechanic said it was the IAC, and other people who know alot about hondas agree.

could it be something else besides the iac?

 

If you really think it's your IAC, try simply cleaning it. That's explained along with some other good cleaning tips here:
https://honda-tech.com/forums/honda-accord-1990-2002-2/cleaning-iacv-fitv-tb-1844067/

I cleaned my IAC and FITV about this time last year, it doesn't take long and it's cheap.
Also, I believe the Haynes manuals for the CB7 (90-93 Accord) have a test procedure to check your IAC.

I've also heard that a vacuum leak can lead to this problem. Here's just what I found with a quick search, it appears to go through more thoroughly diagnosing a roaming/bouncing idle:
https://honda-tech.com/forums/honda-accord-1990-2002-2/help-1992-accord-bouncing-idle-video-problem-2575201/

I hope that this helps!

 

Are you sure he didn't mean FICV? Otherwise, your mechanic is pretty inept.

 

Simkin314: Might I ask what an FICV is for my own future reference? I've heard of the FITV (Fast Idle Thermo Valve) but not an FICV.

Thanks!

 

Actually, you may be right. I've always called it Fast Idle Control Valve (or Cold Start Control Valve). Good looking out, FIT it is...

But if he was talking about that one, that one can be bypassed especially in warmer climate areas (you may not wish to do it in winter climates).

 

joc1394, thanks for posting those links, they were very helpful. i did clean the iac about 6 months ago but i don't think i did a thorough job.

so i got a can of throttle body/air intake cleaner (instead of carb cleaner), cleaned out the iac multiple times, cleaned the throttle body and the pcv, then adjusted the fitv. it seems to be working but i'll run another test in the morning before i break out the champagne.

Simkin314, yes, that mechanic is completely inept and will never go near my car again.

 

Fast Idle control/thermo valve is definitely the culprit, and all it takes is a good cleaning or a "tightening" of the white plastic valve seat to stop the hunting idle. (depending on your situation)

I would take it off, clean it AND tighten the white seat with a little blue loctite on the threads. Should be good as new.

The only other thing I could think of is a random vacuum leak (other) than the control valve.

sohc

 

i think you're right, because i already cleaned the iac once before, the pcv is relatively new, and the tb wasn't dirty at all. i cleaned and tightened the white plastic thing in the fitv and checked for airflow. i honestly think that was the only thing i really needed to do, but i did all the other stuff anyway. the only thing i didn't do was bleed the coolant.

i drove around for about 5-10 miles tonight and based on the weather and the amount of time the car sat cold, it normally WOULD have idled erratically but it ran pretty smooth. this forum is a life saver.

 

Good job man. Sounds like you probably fixed the issue.

 

Good deal! You should probably go ahead and bleed the coolant to take that out of the possibilities, only takes a minute.

 

something kind of sketchy happened tonight. i drove up to the store, and i noticed when i take my foot off the gas pedal, it will surge about 4 times (somewhere between 1000 and 1500 rpms) and then go back to normal. but this is nowhere near as bad as it was before. do you think it might be air in the cooling system?

about bleeding the coolant: do i just open the air bleed on the thermostat housing, and do i need to remove the radiator cap as well?

 

another question: does the EGR need to be taken off and cleaned?

 

Yea, Hondas seem to be notoriously difficult to get perfect.

I didn't think early 90's Civics had EGR (exhaust gas recirculation) valves.

 

This is funny considering what you posted after.

While disabling the IAC will throw a code, it will not leave you with a terrible idle if done properly. If you start the car, and then disable the IAC while the car is idling normally, the IAC's stepper motor stays in the same position that it was driven to by the ECU. Only someone who didn't know how the IAC worked would disable it while the car was off, this would in effect kill your idle. I certainly wouldn't consider the mechanic that suggested this incompetent, some people just need to research more before spouting off about what they think they know.

 

The mechanic that suggested this is incompetent for other reasons, e.g. damaging the drivers side window track then denying doing it, among other things. But he legitimately believes the IAC can be bypassed, so does his father who owns the shop.

 

That's because you CAN disable the IAC, fairly easily on most cars actually since usually it's just a plug to pull. Start the car up and when it's idling fine, pull the plug on the IAC and drive around for a few days like that. If it IS the IAC, it should drive fine and you can either leave it like that or make plans to replace it. If it still surges, you at least know that it's not the IAC and you can then make plans to take it to another mechanic.

 

I'll try that. The only problem I'm having now is when driving slowly, I let off the accelerator and it revs a little bit a few times before going back to normal.