I have a 99 civic EX Sedan. Those of you with similar cars (6th Gen), what speed does your engine typically idle at? Mine usually around 700 maybe but once it sits and warms up for a while it'll drop down to almost 200. Is this normal? My friend's didn't believe me about the low idling speed but I showed them a picture. My friend was saying my MAF sensor is going bad (he is trying to say my car sucks), is this true (the maf part I mean)?

 

A cold engine without load should idle high, about 1500 rpm. A warm engine without load should idle at about 700 rpm.

Is the CEL ON? If not, try cleaning the IACV (see DIY section) and, if necessary, also adjust the idle speed.

 

So that's bad? Yeah when its really cold it idles around 1500 and then drops down slowly as it warms up. A lot of times though once its warm it'll drop down to around 200-300. So that's bad I guess. Thinking about it now, I don't have 1 of the hoses connected to my intake manifold (its the one that sucks air in) maybe that is why?? What is that hose anyways (not the breather one), the one that draws air in. If you plug it the engine starts to kill, maybe its a pressure sensing hose?

 

The disconnected PCV hose is likely the problem. Why is it disconnected? This hose draws filtered air from the crankcase to the intake manifold. It's bad that the hose is disconnected for three reasons. The PCV system can't perform its function of reducing emissions, and your intake manifold is receiving too much air and probably causing the engine to run rich (reduced gas mileage). In addition, the intake manifold is taking in unfiltered air that contains particulates. Your ECU is trying to compensate for the higher than expected air intake, thereby creating the idle problem. In summary, RECONNECT THE PCV HOSE!

 

Yeah its not the PCV hose though, I don't think. The PCV hose is for blowing pressure and crankcase vapors back into the intake to be burned up in the engine right? Also I see many people don't have those connected and have a filter instead. That's not the hose I'm talking about, I'm talking about the other one. And wouldn't more air and fuel mean higher idling speed? Not trying to correct you, I know you know more than me I'm just wondering.

 

Air is moved through the PCV system by suction/vacuum created in the intake manifold. Direction of air movement in the PCV system: Starts at the breather hose connected to the air cleaner, moves to the valve cover, passes through the crankcase, exits out the breather through the PCV valve, and then passes through the PCV hose to the intake manifold.

The first hose you refer to is called the breather hose. The other hose you refer to is called the PCV hose.

Yes but the ECU will try to compensate by lowering the idle speed. The end result is a fight between the ECU and the intake air leak. This fight leads to an idle speed problem.

Why do you have the hose disconnected??????

 

Cause I made an intake last year out of some aluminum piping and an air filter that I bought. I have the sensor inserted in but one of my friends was supposed to weld a bung on for me but he never did. So I guess what I should do is get a new intake.

 

Okay, your modified intake manifold lacks a PCV inlet nozzle. The lack of this nozzle on the intake manifold better explains the low idle problem. Air normally sent to the intake manifold by the PCV hose is absent, thereby reducing the idle speed.

 

Oh you thought I meant like it was leaking out a disconnected area?? Yeah there's no connection bung. So that's still not great I guess right?

 

Correct. Not good. The engine needs a regulated amount of air flowing from the PCV hose to the intake manifold to maintain the proper idle speed.