I have a d16 in a 95 civic and pretty often when im stopped and rev the engine or at idle sometimes I hear what sounds like part of my exhaust rattling. My question is could an exhaust leak cause my car to go below regular idle after revving up? Like if I hit the gas it goes up in rpms, goes down to about 500, then goes up to 800 and stops. I just replaced the IACV and bled the coolant system also.

 

No an exhaust would not cause the rpms to dip like that I would suggest to check your timing.

 

The rattling is almost certainly the cat converter heat shield. I wouldn't worry about momentary low rpm unless it is actually stalling.

 

ill check the shield out today, and the only other thing that's bugging the crap out of me is my car idles up and down at startup. ive tried numerous iacv's and bled the coolant religiously. would a break Line vacuum cause that also?

 

Yes, a vacuum leak would cause erratic idle like you describe.

 

Its weird though like when I first start it from overnight it idles at about 1500 for like 5 seconds then it starts with the up and down idle. Other then that after about 3 minutes of driving it goes back to normal and stays at a steady 700ish.

 

It could be the FITV, which admits extra air upon a cold start. Disconnect IACV when warmed up and adjust the air screw for 400 rpm, and check that the IACV and FITV are not drawing air (take the intake pipe off and block the holes inside the throttle body before the throttle plate.)

Also check the timing as suggested.

 

I cleaned the FITV and bled more coolant and it still does it. I just got done bleeding more coolant, maybe I have a small leak in my coolant lines? I don't notice any leaking though. This is so aggravating.

 

And if its not caused by my IACV or air in the coolant lines, could it be caused from a fauly o2 sensor?