I own a 1999 Honda Accord EX V6 coupe. Ever since I bought it (with about 186,000 miles), it has had and idling issue. Usually after an hour or so of driving, it will start acting up. The engine will start sporadically going up and down between 600-900rpms at first, then as time goes on, it worsens to 600-1300 or 1400rpms. The thing that I thought was strange was that it does not do it in reverse at all. D4 and D3 gears are the worst (it's a 4-spd auto), 1 and 2 OD gears are not as bad, and then neutral, park and reverse are fine, nothing happens in those gears. I figured it was not an electrical problem because no check engine light come on, but then again I'm not an expert. Also sometimes when I start my car after starting it many times before in the same day, the engine will turn over, go up only to about 800-900rpms (normally its about 1,100-1,200) and then ver quickly drop to zero, followed by the engine turning off completely (the radio, lights, and everything electrical will remain on.) I'm guessing that may have something to do with the idling problem.
By the way, I replaced the IAC motor, thinking, along with four other mechanics, including Honda, that a bad IAC motor was the cause, but it didn't do a thing. It is no better than it was before it was replaced. Does anybody have any idea what the cause of the problem could be?
Sorry, I know it's long but I tried to be very descriptive.

 

Are you sure the coolant it full? Air in the coolant can cause the IAC to not get the right reading.

Then there is the IAB - Intake Air Bypass....Has it been tested?

 

By coolant do you mean radiator fluid? And how would I know if there's air in the coolant? If you mean the radiator, it's full, I just recently checked.

And I don't have an Intake Air Bypass, I don't even have a CAI yet, (I will soon)... I probably should have mentioned that.

 

Ok, coolant/radiator fluid/anti-freeze = yes.

IAB is a stock (OEM) part of the intake system.

One thing I forgot to ask before, are the tune up items up to date?

 

I actually don't have a stock intake. I have a makeshift intake made out of electrical tape and an air filter, so I do not have an IAB. It was like that when I bought it. I was actually thinking that perhaps if I got a different type of intake system (like a CAI), it may help? I don't know...

And yes, mostly everything is up to date, if I'm understanding you correctly. Not everything is working properly, however. That is the reason why I need help with this current problem. After this is fixed, I will then know if the other problems will need attention. It's a long story, but this is the first one I need to get taken care of.

 

Humm, could there be an intake leak? Been doing this since you've owned it, a modified air intake system???

What are the highlights of the other issues, could they be related?

 

An intake leak was one thing that we thought could have been the source (considering it's only tape).

One of the other problems are the motor mounts. They need replacing. Not all of them, just a couple. From a stop, IF the idling issue is happening at the time, the engine will slam hard under heavy acceleration (I'm guessing from the bad mounts), hard enough to jerk the car and actually slow it down from the jolt, so it's pretty serious.

The other problem is POSSIBLY the tranny. It slips into gear (only from first to second gear usually). Rarely ever through the other gears, maybe once a month or so it will slip into another one besides 1st to 2nd. It also shifts hard and unevenly sometimes. But that could be the idling problem making it shift incorrectly.

We're not sure if the slamming is from the motor mounts or the tranny.
And we don't know if the slipping is from the idling issue or the tranny.

So basically until we get those fixed, we won't know if the tranny is really bad or not.