It's been a while since I visitied, but here goes. This is a problem I've lived with the past year and I thought I'd put it out there for a possible fix.

I've got a 94 civic DX coupe. Replaced the old motor with a JDM 1.5 Vtec about 14 months ago. Nothing changed internally, but have added headers, new cat, stainless cat back exhaust, Skunk II manifold with a behind the bumper cold ram air induction and an upgraded computer with a reprogamed chip. When I installed the motor, I added all new engine and manifold sensors.

The engine runs great, has good mid range power, but it has what I call a breathing problem at idle. Whether hot or cold, starting after sitting for several days or being driven hard, the rpms at idle will go up and down between 900 to 2,000 rpms. The idle will raise, come down, pause for a moment then repeat. Every once in a while, I can tap the throttle and it will stop for a short time, but then it will continue.

The problem has been since day one and changing manifolds hasn't helped. I've double checked for air leaks by spraying carb cleaner around the manifold and nothing. All the air lines are on tight and nothing is loose. I've readjusted the throttle cable in case the rpms were dipping too low and still the problem persists.

The car passed AZ smog inspection with flying colors and if I stay off the throttle, I can get just under 30 MPG, but average around 25 MPG. The problem is more of an irritant than anything else, but if it's a sign of a possible problem, I want to get it fixed. My local Phoenix area speed shops have not been able to fix the problem, so any help or suggestions would be great.

Thanks

 

Is the CEL ON?

1) Have you tried cleaning the EACV (IACV)? See forum DIY section.

2) You may have air trapped in the cooling system so try bleeding the system. No need to drain the coolant. Just push the heater lever to full heat, top off the radiator and reservoir with coolant, and then bleed the system of air:

 

No check engine light at all. Like I say, it passed AZ emmissions no problem.

Cooling system has been purged and pressure checked.

I will check the EVAC this weekend.