I have a '98 Civic Ex engine (D16Y8) in my '88 CRX with a '94 Civic Si ECU (p28?) and a '95 Civic Si Intake plenum/TB...I also have an intake and headers/full exhaust...

Whenever i start my car...cold or warmed up, the car idles at 3000rpm's and then slowely lowers to about 1200 rpm's after maybe 5 minutes. It's highly annoying and I don't know if it will make me fail inspection as well. I bought the car like this and it has been idling like this since i got it but didn't think much of it. Are there any common problems that may cause this? If i hook my ECU up to a computer, what should i look for that would be a red flag. I hope you guys have heard of something like this before. THANKS!!!

 

is your throttle cable too tight?

 

Two things.
One, it most likely is the fast idle control valve.
That is a valve near the throttle body. it has coolant hoses going to it, but no wires. It must be clogged and it's not working right.
Another possible reason is the EACV.
That is an electronic valve that helps to conpenasate for when there is load on the engine while at idle. It is right next to the throttle body and it has two wires going to it (one plug)
My bet is on the fast idle control valve. When that valve is cold, it lets air go by, but when the engine warms up and hot coolant flows through it, it closes and stops air from going through it. That is most likely your problem

 

I would put my money on the EACV or also known as the IACV. I had a really shitty idle with my Z6 intake on my A6 motor (oh and the Z6 IM is the 92-95 IM) and I knoew my IACV was messed up got a new one and everything is fine. Oh and one other thing that likes to cause weird idles is if your coolant isnt bled properly. And since the coolant goes through the IACV it will give you the messed up idle. Bleed your coolant and then go from there cause the IACV arent cheap.

 

another thing that I ran across on a friends accord...It was so simple...The Idle adj screw some how over time backed out and was only being held in with the vacumn. Still had the OEM hondabond covering it. IACV also could be it. Remove it off the back of the manifold and clean it with some carb cleaner to get the carbon build up out of it.

 

My ECU is from a 94 civic Si and the engine is a 98 ex/si...would the difference between the engine and ECU generate this problem? With my setup (94 si ECU, 98 EX/Si D16Y8 engine, 95 Si Intake) what throttle body/IACV should i be using? Should it match the engine or ECU?

Anyone have a price on an IACV if that is the problem? I read somewhere that they are hard to clean.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by AgentJam &raquo;</TD></TR><TR><TD CLASS="quote">My ECU is from a 94 civic Si and the engine is a 98 ex/si...would the difference between the engine and ECU generate this problem? With my setup (94 si ECU, 98 EX/Si D16Y8 engine, 95 Si Intake) what throttle body/IACV should i be using? Should it match the engine or ECU?

Anyone have a price on an IACV if that is the problem? I read somewhere that they are hard to clean.</TD></TR></TABLE>
OK you got me all confused but I can tell you this much for the throttle body you can use any of them that bolt to it and it would be fine. As for the IACV you will want to get one that matches the intake manifold itself since some of them arent interchangable I.E. You cant use the IACV off of an A6 on the Z6 it simply doesnt fit. As for your setup if I am reading it right everything should be fine. So I take it that your car is setup for obd-1 and not obd-0 right?? If anything what should match up would be the ECU to the distributor other than that it should be fine.

 

Hey Guys!

I just took off what i think is the fast idle control valve...it was on the bottom of my TB. I drained my coolant and unscrewed it and as soon as i did it was rattling. When i took off the plate on the one side the pieces fell out. HAHA! It's ok they are ok, it's just that the plastic piece that holds the spring back wasn't holding it back anymore...i guess letting air through to the engine...a lot of air it looks like. But i was just wondering...would my obd-1 computer try to compensate for it because even on a warmed start, the engine would start at 3000rpm's and then work it's way down to 1200, it seemed like at 200rpm intervals. Like the ECU was saying...hmm somethin is messed up. Anyway i'm about to put it back on...if anyone has heard of this happening...or can confirm that this is the Fast Idle Control Valve that would be great. THANKS EVERYONE!

Oh yeah...if you know what i'm talking about could you tell me if i should worry about tightening the plastic spring retainer down too much? Would this control my idle at all???

 

Hmmm...well i just put the thing back on, filled my coolant and tried to start and it stalled out right away. It did start up and run if i was holding the gas down but that was because i was giving it air. I guess the Fast Idle Control Valve (Or whatever i just took off) needs to be tightened to the right position...anyone know what i should do??? There has to be an easier way that draining my coolant, taking it off, adjusting it, putting it back on, adding back coolant and seeing if it idles right. PLEASE HELP!!!