rpms drop off once engine is warm

DC_T · Post by **DC_T** » Mon Feb 01, 2010 12:07 am

I've had this issue since I got the car running. The car starts and runs perfect, with no idle issues. After driving the car around and getting it up to normal operating temps, when you come to a stop and push the clutch in to throw it in nuetral, the rpms drop off hard and either fall to around 100 and come back up to the normal 850 or so, or drop off completely and the car stalls. I've realized that if you let the rpms fall down to around 800 or so w/ the car in gear then throw it in nuetral it doesnt happen, but if the rpms are any higher, then I have the issue. I had the car tuned at Lowe right after the rebuild, the car was basically on the dyno the first time it was driven. So, I thought maybe it was a tuning tweak that needed to be done. So I took it back to them, they said they checked the tune and it was good, and told me that it was the iacv, and even said they swapped it out for a new one and didn't have the issue. So, I picked the car up, bought a new iacv, swapped it out, and have the same issue. After trying to talk the Lowe (multiple times) I realized they are not really wanting to help me out. No big deal, i've been around this game long enough to realize nobody cares about your car and situation as much as you do, and its a business. But I digress.... So anyways, thats why I am here. Anybody have any ideas? I've already checked for vacuum leaks, swapped iacv, and cleaned the throttle body. Next I was thinking of maybe bleeding the coolant system. Could it be the o2 sensor? Maybe the map is bad? Just really looking for any help you can offer, this problem is pretty annoying. Thanks.

here is my setup by the way:
lsvtec, b16 head, b18b block, pr3 pistons, gsr cams, chipped p28 tuned w/ hondata

tommygun89hb · Post by **tommygun89hb** » Mon Feb 01, 2010 4:52 am

Do you have a Fast Idle Valve on your throttle body.

you can find on the net how to ajust this its really simple.
Its a little box connected on the TB.

This is my only guess as because you already checked the IACV.
You may have got some plugs mixed up too. on some of the sensors.

I would make sure the plugs are good first before I mess with the fast idle valve.

tommygun89hb · Post by **tommygun89hb** » Mon Feb 01, 2010 5:21 am

Heres a discription of what a Fast idle Valve Does and ways to test it.

DOHC VTEC Fast Idle Thermo Valve from Honda Motors, Japan. This fast idle thermo valve format is usually found on Honda Acura Integra Si-V SiR-G GSR B18C DOHC VTEC. It may also fit other applications. Buyers, please email us and make your own checks if uncertain regarding your application. This fast idle valve is usually fitted horizontally and bolted below the throttle body.

16500-P72-900 is interchangeable with 16500-P72-000

To prevent erratic running when the engine is warming up, it is necessary to raise the idle speed. The fast idle air bypass valve is controlled by a thermowax plunger. When the engine is cold, the engine coolant surrounding the thermowax contracts the plunger, allowing additional air to be bypassed into the intake manifold so that the engine idles faster. When the engine reaches operating temperature, the valve closes, reducing the amount of air bypassing into the manifold.

As the Fast Idle Valve is factory adjusted, it can be installed or removed but not recommended to be disassembled.

The Fast Idle Valve is a component whereby when faulty can cause some starting and idle-linked problems. The problem is symptomatic and will not trigger the Check Engine light. The list goes:

Difficult to start engine when cold
When cold fast idle out of spec (1,000 - 2,000 rpm)
When warm RPM too high

In many cases, you can test whether your Fast Idle Valve is working by putting your finger at the lower port of the throttle bore, located at 8 o'clock with the throttle body upright. When the engine is cold, you should feel suction and when warmed up (cooling fan comes on), there should be no suction.

#it sounds like to me if you have one of these that it is stuck open#

civicex442 · Post by **civicex442** » Mon Feb 01, 2010 6:34 am

i didnt read any of the two posts above me, but if you need any help give me a call. i understand your frustration!

DC_T · Post by **DC_T** » Thu Feb 04, 2010 3:36 am

thanks tommygun, i actually didn't think to check the fitv, i will do that as soon as we get a semi-warm day so i can get out there

Joe! thanks for the offer man. i sent you a pm

DC_T · Post by **DC_T** » Thu Mar 25, 2010 1:23 am

hey guys, well, this problem isn't going away. i do not have a fitv on my throttle body, so i can't check that. what i've done so far:

- pulled all the plugs and checked the gap
- played with the distributor a little, tried 3 different positions along the little slot, didn't do anything (for the idle issue at least)
- cleaned the throttle body
- replaced the iacv with a new one
- adjusted the throttle cable
- adjusted the idle screw
- checked all the sensor plugs to make sure they are right
- checked and no vacuum leaks
- checked the fuel pressure, it stays steady at 40psi

the fuel pump has been replaced, the cap and rotor is fairly new although i'm debating on replacing them to try to eliminate some stuff here. when i had the engine out, i did replace the fuel line w/ a stainless steel line and inline fuel filter, don't know if maybe the filter could cause an issue. after the car warms up to normal operating temps, i can sit there in nuetral and blip the throttle and duplicate the problem. not to where the car will die, but the rpms drop low enough to where it almost does. other than this issue, the car runs really strong. the idle stays pretty steady at around 850. i have noticed when i have the brake pedal depressed that the idle tends to move a round a little, but that means from about 700-900 or so. nothing crazy.

this engine was in my car about a year ago w/ everything exactly the same except for the inline fuel lines and the rebuilt bottom end/tune. i also did a wire tuck while i had everything out, but was careful to cut/extend/solder only one wire at a time, so i'm pretty sure that all of that is ok, although i'm not going to completely rule anything out at this point.

i've been all over forums and can't really find much info to help so if any of you guys have any more suggestions, please throw them out there.

thanks in advance

5thgen · Post by **5thgen** » Thu Mar 25, 2010 1:28 am

what is it tuned with?

Did you set the idle with the iacv unplugged?

DC_T · Post by **DC_T** » Thu Mar 25, 2010 1:54 am

5thgen;226284 wrote:what is it tuned with?

Did you set the idle with the iacv unplugged?

chipped p28 and hondata. lowe tuned it for me on their dyno.

no, i did not set the idle with the iacv unplugged. i just replaced it, plugged it back in, and started the car up. is there a proper way to set the idle when you replace the iacv?

5thgen · Post by **5thgen** » Thu Mar 25, 2010 1:58 am

I believe the honda/helms says to unplug and set idle to ~400 or 500. Plug the iacv back in and reset ignition.

Im going to double check

It says to unplug....stabilize idle to 480rpm. Shut off, plug in, turn on again. I don't know if it'll help....but worth a try I guess.
*do this at operating temp

RyanA · Post by **RyanA** » Thu Mar 25, 2010 11:04 pm

Unplug your IACV and start the car. It should idle around 750 or so with it unplugged. If it does not, adjust the idle speed with the throttle stop screw or the idle bleed screw. Once it idles at around 750 with iacv unplugged, check your TPS voltage. Plug IACV back in and start car and go drive.