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Idle to high when cold, and goes up and down!

09-28-2004, 05:11 PM
Hey guys,

I recently installed a cold air intake on my 93 lude, car was fine, now recently when i start the car up in the mornings rpm goes to about 1500-2000 and then jumps up and down intermitently, although as i drive and car starts to get hot the problem goes away.

Can anybody tell me what is wrong and how i fix this?

Also sometimes car wont start, especially in hot weather, then it starts and dies immediately and then it will just start after a while no problems.

Some help please :)


09-28-2004, 05:16 PM
I have a 92 prelude stock and I remember reading in the manual the car idles high when cold then when attaining proper temp it idles normal. I'm almost positive this is the case as I read it in the manual.

09-28-2004, 05:17 PM
although the rpms shouldn't go up and down erradictly

09-28-2004, 05:19 PM
yeah thats it, the idle shouldnt go up and down like that, besides it never reved so high as to 2000rpm when i started the car, i can actually hear the car a bit too accelerated.
any body knows what this is?

09-28-2004, 06:33 PM
Check out this thread on this page. I had the same idle condition.
Idle problem... seems different posted by: Flava888

10-15-2004, 08:15 AM
i got a 86 2Lsi that does the exact same thing so i know what u talking bout, except my lude is rooted so i cant put my finger on the exact solution, but im pretty sure something is wrong with your cooling system, like mine. Ive had a quote and they said that my radiator or theromo was blocked by something or other, plus my over heates and pisses out steam from the over flow resevra when i turn her off.....

10-21-2004, 06:37 PM
Try this, some stuff that I had saved. This is from an old post from here, sorry I don't have his name for credit. I just plugged mine, but that may not work in cold weather. If anything gets loose in there it will be sucked into the engine. Plugged the 7 o’clock hole with a wooden dowel inserted into a rubber hose that fit the hole.

Honda Civic Si Electronic Air Control Valve EACV also known as IACV. It can be fitted to Honda OBD1 & OBD2 intake manifolds.
The EACV is an integral part of the idle control system. It changes the amount of air bypassing the throttle body in response to a current signal from the ECU in order to maintain proper idle speed. After the engine starts, the EACV opens for a certain time. The amount of air is increased to raise the idle speed about 150-300 rpm. When coolant temperature is low, the EACV is opened to obtain the proper fast idle speed. The amount of bypassed air is also controlled in relation to the coolant temperature.
When Check Engine light is on. With the service connector jumped, CODE 14 is indicated. It is highly likely a fault relating with the EACV.
The EACV is a component whereby when faulty is the most probable cause to most idle-linked problems. The problem can be symptomatic and may not even trigger the CEL. The list goes:
When cold fast idle out of spec (1k - 2k rpm)
Rough idle
When warm RPM too high
Idle speed is below specified rpm (no load)
Idle speed does not increase after initial start up
On models with automatic transmission, the idle speed drops in gear
Idle speed drops when air-conditioner is ON
Idle speed drops when steering wheel is turning
Idle speed fluctuates with electrical load
Frequent stalling while warming up
Frequent stalling after warming up
Bidders should do their own check to make sure the other sub-systems or ECU are working well before making their own conclusions.
The EACV is tested with a multimeter. The result is at 12.5 Ohms which falls within the acceptable range. Make your own checks to see whether this EACV suit your needs. The EACV in the picture below is the item you are going to get. Check it out supersize.

1) Let the car warm up. Just let it bounce or surge and do its thing. When it is up to temp.
2) Take off the intake pipe.
3) Look in the throttle body
4) There will be 2 holes, one at 7 o'clock and the other at 9. The one at 7 is the idle bypass and the one at 9 is the cold start bypass. Getting more air helps the car heat up in cold weather.
5) Now stick your finger in the hole at 9 o'clock. This will mimmick the cold start valve closing. Don't worry it won't suck your finger in.
6) If when you stick your finger in the hole the idle goes back to normal then that is the problem.

This is the racerx fix, named for the creator of this (TEMPORARY) solution. The root cause of the H23 idle bounce its that the elastic plug that expands in the fast idle valve, has lost its elastic properties and no longer expands/contracts the same distance. This repair prevents the necessity of a $65 dollar part and and $100 labor charge (if you are lazy). I have driven on my car, and changed the oil, flushed the cooling system, and driven the car, in ummm"spirited" driving since and the idle holds fine.

Tools required
Socket Set 3,6,8mm
Socket extender
1 flat head screwdriver
1 phillips head screwdriver

Tools Recommended
1 extra flat head screwdriver
several screw type hose clamps 1/4-3/8"
Mechanix style gloves
Several lengths of extra cooling hose
Coat Hanger-wire

Follow the intake to the throttle body. directly below the throttle body (TB) is a cylinder, with a flat, copper plate capped end. That is the fast idle valve (FIV) . The throttle position sensor (TPS) is the electric clamp on the firewall side of the throttle body, the throttle cable is connected to the rocker on the front of the TB<BR

1) Open hood, and prop open with a 2x4, or something a bit longer than the post in your engine bay. I recommend disconnecting the battery before working under the hood.
2) Take the Sharpie and number all the vaccuum and coolant lines that run to the Intake, TB, and FIV.
3)Remove the Intake pipe and air filter.
4)Disconnect the TPS.
5)Disconnect the Throttle cable (Don't unscrew the placement nuts unless you want to tighten your throttle cable.)
6)Disconnect the coolant line to the FIV, some coolant may spill out, but its less that 50ml usually7) Using the 8mm sicket and extender, unscrew the 4(four) 8mm bolts. Becareful not to drop them, because fishing them out of the engine is a pain (and that is why the coat hanger is on hand)
8) Once all 4 are done the throttle body will slide on the posts to the intake mani-chamber. As it slides for forward there is a bracket on the bottom of the FIV Cylinder. It has a clip that routes electrical lines, unscrew this bolt 6mm with the socket wrench.
9) The entire TB and FIV assembly will slide out
10) Take this to a flat clutter-free workspace. Inspect the assembly, particularly the FIV. On one end there is a Copper Plate secured with 2(two) 3mm/Phillips head screw/bolts. Use the Sharpie to mark orientation, then remove bolts, and copper cap11) Inside is a white retaining ring with a copper "bullet" through the center. Mark approximately how many threads this ring is screwed into the assembly. Using the flathead screwdriver(s) gently unscrew the white retaining ring. Once removed, "dump" out bullet assembly12) Remove Spring Clip on end of bullet assembly -CAUTION, the spring clip will get shot across the room, garage, or driveway.- Pull the spring off the assemebly. Once off gently, but firmly stretch the spring until you feel it deform slightly. This is re-tensioning the spring to take into account the loss in elasticity of the wax plug. 13) Reassemble the bullet/spring assembly, and replace in FIV.
14) Reinstall white retaining ring, and screw approximately same number of threads in, plus 2-4. This is opening the FIV, slightly allowing more air around it after ignition, but putting more pressure on the wax plug, and spring assemblies, so that any change in temp will close this hole. (ALso this is why this is only a temporary fix, as in time this will break down again)
15) Check TB/ Intake Manifold gasket for fold, dirt, grime and or damage. Replace as necessary.
16) Reassemble everything in reverse order. Install new hoses and clamps for old, and damaged parts.
17) Reconnect TPs
18) Reconnect throttle cable, and tighten as desired.
19) Reconnect battery.
20) Start car and observe. Adjust idle as necessary with flat head scredriver at idle screw. (Top center position over TB) I recommend opening the radiator cap for a few minutes to "bleed" the cooling system as well. Make sure it is recapped promptly though.

21) Got to the bar, celebrate liberally Your car's idle will no longer wake the dead.

It maybe necessary to re-adjust the tightness, the number of threads, of the white retaining ring, to get a stable idle. Disconnecting the battery for that period of time resets the ecu, as well as all internal (radio, clock, and other electronic goodies) So you might want to record favorite stations, stereo equalizer positions, and/or dvd settings etc.
I believe on the prelude the four throttle body bolts are 12mm. and remember to torque them down to 16ftlbs. Now what i did for my fix on this is a bit different but works and "may" be better if you have done the coolant bypass mod. What i did was i removed the throttle body same as described above, but instead of dealing with the removing of the spring and wax thingy.. i just took off the whole fast idle valve, created a gasket that left no holes open and sealed off the fast idle valve from the throttle body. which basically is putting the gasket between the throttle body and fast idle valve, then re installing the fast idle valve to the TB and putting it all back on the car.... no more surging idle and everything works fine..... if you would like more in depth details do let me know... im keeping this semi short because i dont know if it will be here like my last post.. that disapeared. thanks

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