All,

My car now idles at 800rpm with no accessories on. When any load is placed on the motor the idle drops to half that. (vibrates to).

My question is what should the idle difference be between base idle (800rpm) and idle when under load? I am trying to figure out if my car needs more work or if this is just how it is.

 

It helps if you tell us what type of Accord you have. Place this info in your signature line so it's always available.

In any case, all Accords in US since 1990 and some earlier models have an idle compensation system which controls the idle speed with a closed loop control system. The ECU monitors idle speed and compensates by increasing or decreasing air flow through the Idle Air Control Valve (IACV) which causes engine fuel control system to add/reduce fuel flow to engine to manage the engine load change.

Engine speed should not change significantly as load is added or removed. If it does as yours the IACV is likely not working (damaged or dirty). It can be tested (check solenoid motor) to verify it's functional, and cleaned (remove and clean passages, screen), clean throttle plate on both sides, and throttle body bore carefully w/ throttle body cleaner.

If you have a shop manual, the IACV system should be in that manual.

good luck

 

Texas,

Im very sorry I didn't even realize I forgot to post it.

1994 Accord EX 5sp 2.2 154kmiles

I have a Chilton Manual but it doesn't not show many details. I've been told the haynes manuals are better? If I am correct the IACV is a "cylinder" attached to the back of the intake? Looks kinda like an oversized camera film tube?

 

Yes, it has two coolant lines, inlet and outlet. W/ some difficulty you can remove the 2 bolts which retain IACV to the throttle body and access to clean. Gloves essential.

The electrical connector can be removed to check the IACV solenoid. I don't know resistance spec but would estimate 3-5 ohms (not much so good VOM set to lowest range necessary to check). If open circuit or dead short, then solenoid is defective.

good luck

 

I should be able to get it off, does it require the cooling system to be bled afterwards?

The car will idle at 800rpm but when I drive it without the accessories it will usually stay at around 1500. A friend of mine told me this is the motor keeping the RPM up to burn off excess fuel vapor. Would this be more of an issue with the FITV?

I apologize for the multitude of questions, I am trying to avoid annoying people with multiple posts.

Thanks for the info and your time Texas.

 

The IACV is not removed completely. The coolant hoses remain attached. Of course you could disconnect the hoses to make access for cleaning easy, but you will have to add coolant as you will lose some. Pinching the hoses w/ vise grips before disconnecing should reduce the coolant loss.

FITV is not a typical cause of this problem in my experience, but others may have different opionion.

good luck

 

Thanks for the info Texas. I am going for the FITV as well since I will be in there cleaning and the car has 150k miles on it. The previous owners do not inspire any confidence in me that they took even the slightest care of the vehicle.

This idle issue is getting very annoying and gets much more so when the A/C is on. I would take it back to the mechanic working on it but I can't spare another week for him to get to it only for the same problem to happen again.

I will post back if I run into problems, thanks again Texas!

 

Texas,

I removed both the FITV and IACV and cleaned both. The filter screen on the IACV was a black as satan's heart and clogged. So I cleaned them both out and when I started the car back up it idled perfectly. I turned on the AC to max, headlights on high and the car dropped about 200 rpm. It was beautiful, and then the problem started again.

Now the car will base idles at 1500 rpm with no accessories on, when the AC is kicked on the rpms will drop from 1500 to about 500 and then back to 1000, back down to about 400 and just keeps rollercoastering.

Would this sound as if the IACV is faulty? Any other suggestions you may have as to where this idle problem is? THanks again for your time.

 

Did you clean the IACV valve movement? It may be sticking. It needs to be cleaned carefully to avoid dousing the solenoid w/ carb or Throttle Body (TB) cleaner.

Also clean the TB throttle plate (both sides) and bore around the plate thoroughly.

You may also have an intake air leak somewhere. Check PCV system, vacuum booster, vacuum lines for leaks.

good luck

 

When I had the IACV out I was going to remove the coolant plate and try to get in there but the screws wouldn't budge. I ran a whole can of TB cleaner through the opening until it came out clear. Since I can't get that plate off to get inside it would I be better off replacing the unit?

I took a second and cleaned out the TB intake and the valve inside. I thought I had let it air dry long enough but the car ran like crap until it burned it all out.

I haven't check for vacuum leaks yet. (I was hoping that that wouldn't be a problem but I guess I should have expected it with a 17 year old car.)

Thank you for your help and advice so far.