On a D16Y8, what causes engine idle to surge up and down continually? I checked my repair manuals in the troubleshooting section, but it only talked about engine idling too high or too low, or a rough idle. Can anyone help??

 

a few things like air in the cooling system, possible head gasket going bad, ...etc.

 

some of the time it's the IAC valve, but if it was, then the check engine light would flash.

Otherwise, it's most likely a vac leak. What you can do is spray carb cleaner around mating surfaces, such as throttle body, intake manifold to head, map sensor, etc. If the car bogs down when you spray in a certain location, then you found the troubled area.

 

Locate the fast idle valve..inspect it, verify that`s not the problem before you start throwing $$$ at the engine.

 

Well this is an engine that was just dropped in the car. The head gasket is brand new, and there are no CEL's.

As for the fast idle thermo valve, on 92-95 Civics and 94-95 Integras, it's a little black thing with 2 vac. lines, a harness connection, and a rubber cap on top, right? On the Y8 it's different, and mounted to the fuel rail I believe. Since this engine is using an OBD1 D15 harness, we had to use the fast idle thermo valve from the D15, which is slightly broken. Could this be it?

 

Air filter needs to be replaced. There are a few things it could be though.

 

it's not running any intake or filter at this point, at least not when we were testing it last weekend, just open throttle body.


[Modified by PatrickGSR94, 5:36 PM 3/29/2003]

 

That`s where I`d start

 

hold up a sec, is the fast idle thermo valve underneath the throttle body, or is it on top of the intake manifold? If it's on the bottom of the TB w/ coolant hoses going to it, then that part isn't broken. However the Y8 TB doesn't even have a separate piece on the bottom like the D15 TB does. However the idle still surges no matter which TB is on there (D16Y8 or D15B7 TB).

 

Was the car hot? Because if you are getting surging RPM's, its usually the Air Flow Sensors. Plus, if you were running open throttle body, its sucking in extremely hot air. When the sensor heats up, it doesnt read accurately, and your car will go into kind of a safety mode that just revs the car when its about to die, and then lets off when it thinks it can idle, so it will drop to like 400, then up to 1200rpms. There will be no CEL because the sensor still works, but it cannot read accurately due to extreme temperature.

That has happened to my DOHC mitsu before. The underhood temps get really hot with intake, and it would mess up the air flow sensor. Also, on 6gen accords some people have had the same problems, and they were fixed by reducing temps to intakes. Just a thought

 

what about the air temp sensor? The D15B7 sensor sits in the intake manifold, and the Y8 one sits inside the intake pipe, and since we are using the D15 engine harness and temp sensor, it's just hanging out in the engine bay right now. What have other people done with that? People that have put a Y8 manifold into a 92-95 Civic, what did you do?

 

vacuum leak