1991 Honda Accord EX, 4 Dr Sedan, FWD, ...

I have recently refurbished most parts in Engine area, @ Professional Mechanical Shop, as included below:

1. However, aft changing these, Idle speed was surging, 1k-2K in Neutral, and surging forward at stop signs in Drive, (so had to put in Neutral at Traffic lights, annoying ..).. then changed IAC twice, AND 3 mechanics can't figure out what is wrong even after adj idle via distributor,... they have cleaned IAC also,..
2. Disabling IAC w Solenoid has bypassed this problem,,, I have videos, of idle speed with IAC plugged in (Surging ), and w/o plugging it in (no Surging,..),...
3. The following were changed bef I had this problem

• Spark Plugs, Wires,
• Alternator, Starter, Belts,...
• Fuel Tank, Fuel Pump, some Fuel & oil Lines,..
• Radiator, Condenser, Hoses, Rad Cap,..
• Timing Belt & Water Pump, Tensioners
• Oil Pan & Gasket,

Car was parked for few yrs during Covid, but before that, the Car used to drive really well, high speed was smooth, 100-120-140++ kph easy,.. smooth, quiet, normal Idle,... altho Fuel Tank & Rad had started to leak, rusting, so had bought another car, and parked this one,..

Three (3) diff experienced Mechanics have played with IAC, and have changed both IAC valves (one w Solenoid was changed 2x!), and the Fast idle Valve also changed,.but no luck.

Currently, and even before these repairs, with IAC UNPLUGGED, car feels it has enough power, and has v good acceleration for a 23 yr old car, No sputtering ! (==> so NO vacuum leak?) & (NO defective Airflow sensor?),...

I have seen videos of surging problems on YouTube,.. and if anyone has any more suggestions,..

Thnx

Az_99

 

I recently fixed my issue and it's not where you think it is.

First, check vacuum leaks. The mechanics probably have already checked it but check it again especially on the gaskets (TB, IM). Also replace all vacuum lines, check pcv valve. Clean EGR and FITV. Try replacing the MAP sensor if you have an extra, they don't always go bad but it's not impossible.

My issue was in the Brake booster. Try pressing the brake pedal on idle and see if the RPM changes. If so, check for vacuum leaks around there or replace the whole assembly.
Also try calibrating TPS if none doesn't work, rarely goes bad too but check it.

Try burping all the air on the cooling system for an hour and see how it goes.
Lastly, try resetting ECU after all this work and leave it idle for an hour and see if it relearns.

Other than that, try swapping ECU or getting a tune.

 

Well, I learned something today, but first I assume that you tried the fix that works 99% of the time? Perhaps the EX doesn't have this as I assume by Kiju's post that he knows that this is not on the EX model or he would have mentioned it.See video if your car does have the standard Idle control.
Also, your car would be 32 years old, not 23 years old.

To hijack the thread a little bit. I didn't know that you could tune an ecu in this era.
I didn't know that there was an IAC in this era of Honda as I don't recall ever seeing one on my Hondas. (90-93). But then again, I don't have an EX, just multiple lX's.

 

I believe it's also called FITV. Not really sure but they look like FITV on my H22 with the white plastic looking on the inside and you turn it snug and sometimes remove idle issues as well.

I didn't read the first part where he mentioned his car and I assumed it's a universal issue haha. It's interesting to learn that some Hondas don't have that, or even by their models.(90s')

 

Az 99
Have you tried spraying starting fluid (propane torch, just gas no flame) or less preferable to me WD-40 (lowers engine RPM) across any vacuum hoses, ports etc. You do this to see if the idle changes or goes up to indicate a vacuum leak in that area.

 

Thnx Kiju & Micro1989 LXi
Between the 3 mechanics, they have tried to clear out air in the system (let car run, w/Rad open - idle was better for few min, but same again aft,..), checked hoses, cleaned Fast Idle Valve, and IAC. they opened & sprayed these,... so I don't think they did anything w EGR or MAP if it does have one!.

In the meantime, we have unplugged the IAC Solenoid Valve, and the car DOES NOT surge, but is a little jerky, as if missing in low gear, at slow speed, in Low Gear only, but o/w v smooth at other speeds. I am wondering if I am doing damage by unplugging IACV ?
Az,..

 

Idle should be around 400-500 rpm fully warmed up with IACV unplugged. Haven't driven it without the IACV but from your situation, I think your base idle isn't set to normal. It should be fine to drive IACV-less without issue so I'm thinking your base idle should be adjusted. Also I don't think you're doing any damage as it only affects the idle, not sure.

 

I had same issue on my '91 ex. I jiffy deleted the iacvalve. You will need a small solid plate some rtv adhesive, a coupling for the hoses and a couple screws. There are videos on you tube that go into detail about how to delete it.. only downside supposedly is that you have to let your car warm up longer in the winter or when it's cold out, gets rid of the surging idle, or at least it did for me.