1997 Honda Civic 1.6 surging idle up and down

So with this vehicle I changed the iac and bled the cooling system and the idle continues to go up and down. What did I do wrong. Iac is brand new. I tried adjusting the idle screw in and out, but it achieved nothing. Thanks.

Hi moroso,

You should check for a vacuum leak or any broken hose connected to intake manifold.

Ok thank you. I will. But this particular throttle body doesn’t have any vacuum hoses. Just two hoses for coolant to run through.

MOROSO321 wrote: Ok thank you. I will. But this particular throttle body doesn’t have any vacuum hoses. Just two hoses for coolant to run through.

More than just on the throttle body, if you have a smoke machine you can use that for finding vacuum leaks.

hey guafa, check this out. when i placed my hand over the mouth of the throttle body, the surging stopped. it started idling ok. what is that telling me sir?

I sprayed soapy water like paul does it. but it showed no vacuum leaks yet.

I'm sorry. I need to make a correction here. I have 2 hoses in the back of the intake. One going to the brake booster and the other to the fuel regulator. Checked them, no change in idle speed.

no smoke machine, i wish. just a spray bottle with water. lol

Hi moroso.

That maybe is telling you that when you strangle air intake, A/F ratio is stichiometric or rich. If you check O2 voltage, you could see a rich output.

Do you have additional inputs from engine sensors?

I have the map sensor and another sensor on the air duct. But I probably installed the wrong tb gasket. Because when I cover the mouth of the tb, the surging stops. So what is that telling me. Thank you.

When you cover the t.b mouth, you change A/F ratio. For certain coolant temp.(ECT)/air temp (IAT)/ vacuum (MAP), ecu moves into a certain range of injection memory maps. According to some ecus i have studied, modifying sensor inputs you can reach those limits and ecu is not able anymore to keep stichiometric mixture.

It could be posible you are taking ecu to that limit and getting a rich mixture (you can check if so, by checking O2 sensor voltage)

Do you have any other engine inputs for you from a scannerdanner or any app? Those allow you for a better understanding of the issue you are facing

MOROSO321 wrote: Because when I cover the mouth of the tb, the surging stops. So what is that telling me.

I believe that is telling you that you definitely have a vacuum leak. A vacuum leak on a Speed Density Engine will cause a high idle. If the PCM has a rev limiter programmed into it, it will kill the injectors to prevent over revving. When the RPMs lower, the injectors kick back on and the cycle repeats. This is what causes the surging. If you can block the throttle body intake, with your hand, and the engine does not stall, you are receiving PLENTY of air for the engine to run from an UN-authorized source.

I suggest returning to the water bottle, while blocking the Thottle-body intake.

You should check for a vacuum leak in gaskets (tb to manifold, iac to tb, manifold to cylinder head) hoses and any other hole associated with intake manifold.

When you cover tb mouth, besides constant rpm, do you notice a lower than normal idle speed?

Ok pole71, I will use water while covering the area. By the way, when I purchased a new throttle body gasket, it did not look like the original. I’m going to put the old one back and see what happens.

When I cover the opening, the surging stops and begins to idle normally.