I have a 99 Honda Accord 4 door V6. I had some transmission work done in 2012 to fix a leak and ever since my car does this unusual thing on the freeway. I'll be coasting at 70mph at about 2200 RPMs and my RPMs will increase by 200 all on there own and suddenly drop and I can feel my car jerk. My speed doesn't go up at the time, just my RPMs. I've taken it to the dealership and they've flat out told me "we don't know what's wrong with your car." Recently my car has been starting, then idling roughly and will turn off. I took it to the dealership again and it was the same answer of "we don't know." My neighbor who works on cars and dune buggies suggested it could be my IAC (idle air control valve) and through research online and this forum everything seems to point to my IAC going out. Anyone have or had this same issue? Or maybe think the two could be related solely to the IAC itself? I'm not sure if it would have lasted me 2 years now if its been going out since my transmission repair. I want to be almost 100% sure I need to replace my IAC before I do it. Honda has quoted me about $600 and independent mechanics about $400.

 

As a suggestion, it sounds kind of like your torque converter is going in and out of lockup mode.

 

I just googled that and it makes sense, but its gonna cost a pretty penny to fix. Do you know what would happen if I never fix it?

 

Honda IACVs tend to respond to cleaning, it's more unusual for them to actually fail.

But the idle control system wants to be set up in a very specific way, so look for a thread in the DIY section about setting the "BASE idle".

Vacuum leak?
Dirty throttle body?

Torque converter locking up sounds reasonable for the issue while driving, but not for the idle stuff.

 

Before doing any trans work, have you changed trans fluid recently.

Also, does check engine or D4 light ever flash? If yes, get codes read at auto parts store and post them (actual code Pnnnn).

good luck

 

I don't have any check engine lights on (I really wish I did because that would make solving my problems much easier) and I've never seen my D4 light flash, but I'll be extra aware of it now if it does. My transmissions fluid was changed when I had transmission work 2 years ago. Do you think I would need to get it changed again?
When I spoke to the Honda service technician they said there IACs only fail and cannot be cleaned. I really hope that the service technician isn't lying. I will definitely try to set up the base idle.

 

dont just assume there isnt a code check it

 

I would change trans fluid; drain/replace cycle using Honda ATF. Sometimes this simple item improves trans performance. Failure of lockup can be lockup solenoid (easy to fix) or hydraulic fault (not fixable w/o removing trans).

IACV can be cleaned. See DIY forum and youtube for guidance (any honda/acura V5 of that vintage will be similar) Shops don't clean them because they can sell you a new unit at 50-100% markup. Why clean?!

Agree that you should check for codes. I think there are some trans codes that don't set Check Engine Light or flash D4.

good luck