Weird Idle Problem

Hey guys

I am working on a 95 Civic LX 1.5L 16 valve for my buddy. We changed out the timing belt, water pump, thermostat, plugs, wires, brakes, and a few more minor things. When we started it up, it did the normal rev up to 2500 to warm up but when it died down to normal idle it started reving up to 2000 and back down to 800 about every second. It is the weirdest thing. It ran fine before hand, I have cleared out the computer and checked vacuum lines and looked for anything that seemed out of place. Has this happened to anyone else or does anyone have any ideas?? Any help would be appriciated!

did u put coolant back in it? did u unplug any sensors? did u get the timing off by a tooth? 2.5k is pretty high even for cold idle, mine is between 1.5-2. u might want to check the idle adjustment. wut were the few other minor things that u didn't mention?
make sure u don't have any air bubbles in the cooling system, make sure the timing belt timing is right, check the idle adjustment, i'm guessing u have an idea of wut u'r doing so don't take offense if some of the items sound simple. just clearing the basics so they're ruled out.
if all that checks out, try tapping on the iac valve w/ a screw driver while it's rough idling, if it clears up or changes rpm for a moment or more, then it's a bad iac valve.

-edit: also check for a vacuum leak, but one to cause that would be a pretty noticeable one

Check for vacuum leaks as well as which spark plug wires are plugged into where....

Hey guys

I am working on a 95 Civic LX 1.5L 16 valve for my buddy. We changed out the timing belt, water pump, thermostat, plugs, wires, brakes, and a few more minor things. When we started it up, it did the normal rev up to 2500 to warm up but when it died down to normal idle it started reving up to 2000 and back down to 800 about every second. It is the weirdest thing. It ran fine before hand, I have cleared out the computer and checked vacuum lines and looked for anything that seemed out of place. Has this happened to anyone else or does anyone have any ideas?? Any help would be appriciated!

Take your IACV out and clean it with carb cleaner. A dirty IACV will give these kinds of symptoms.

Take your IACV out and clean it with carb cleaner. A dirty IACV will give these kinds of symptoms.

when cleaning throttle bodies, u avoid getting carb cleaner in the iac because it can damage it. soooo... u might not want to clean it that way

when cleaning throttle bodies, u avoid getting carb cleaner in the iac because it can damage it. soooo... u might not want to clean it that way

Do you say this from experience? I've used O2 sensor safe carb and choke cleaners on TB's IACV's and FITV's of Hondas and Toyotas and I've got nothing but good results. Please tell me where you heard that it can damage it.

i had one myself go bad after cleaning w/ carb cleaner, then in class was told that iac's can be damaged by carb cleaner. maybe it's not a sure iac killer but it can do it. the way i figure it does this- the carb cleaner, if not cleaned out of the iac after, eats through the seal of the needle/plunger and gets into the motor and contaminates the motor and thus damages it. like i said it may not happen all the time and if the carb cleaner is cleaned out of the iac after then u may be able to avoid damaging it.

eats through the seal of the needle/plunger and gets into the motor and contaminates the motor and thus damages it.

Contaminates the motor? It was built to clean/ combust. It is 100% combustible. What do you mean by contamintes the motor and thus damages it? That seems like a pretty weak explanation. Carb cleaner is meant to be sprayed liberally down intake ports; any excess is combusted in the combustion chamber.

Contaminates the motor? It was built to clean/ combust. It is 100% combustible. What do you mean by contamintes the motor and thus damages it? That seems like a pretty weak explanation. Carb cleaner is meant to be sprayed liberally down intake ports; any excess is combusted in the combustion chamber.

the iac motor. there is an electrical motor that is part of the iac. that is wut controls the amount of air that is allowed to bypass the throttle plate. i know carb cleaner is combustable, but when u clean carbon off w/ carb cleaner, it has to go sumwhere the carbon doesn't disappear. in the case that the iac is damaged it's likely do to carbon being introduced into the iac motor by way of the carb cleaner.

my car does that too. except mine goes up and down from 3,000 to 1,000 every second. gah. once the engine warms up it stops though. i wish i could help ya.

check your fuel pressure regulator.

If there are air bubbles in the coolant syste, will it affect the tempurature? mine idles just like this but the temp stays normal.

If there are air bubbles in the coolant syste, will it affect the tempurature? mine idles just like this but the temp stays normal.

Yes, make sure you bleed your system. I've seen air in the coolant cause both funcky idle and overheating problems. Run the car to op temp then oben the bleed screw near the upper radiator hose and let the bobbles flow out. Even though your temp is normal you could still have enough air in the system to throw off your idle.