Today, I was dropping my brother at work. I drop him off and i start driving off, and when i came to a stop at the stop sign, I notice my Rpm is literary at zero!! But the weird thing is, to my knowledge, the car should stall, but it does not, the engine is idling fine with no shaking or any signs of it wanting to stall. I keep driving, and it is doing the same for the next 4-5 minutes, when i come to a stop. But then about 5 minutes later, it was idling normal.

Normally it idles at about 400-450 rpm, does that seem right? I thought it looked a little low, but when couple of guys checked it out, they said it was normal, so i didnt bother looking further in to it.

Also, I have a system in my car, and when i pound the system, and im at idle, the rpm dips down and up, so i figured i am straining the alternator/battery. So i go and buy a Capacitor and hook that up , and I still see that the rpm is dipping low. About 2-3 months ago, when I first bought my system, the shop i bought it from told me my battery is kinda of weak. Stupid me didnt bother looking in to that and had the system installed. about 2 weeks later, my car went wack and i couldnt even drive the car, i jump start the car, and the rpm gauges were going crazy and the car wouldn't wanna move when i accelerated. I got it towed to my mechanic, and he told me to replace my battery, so i did with a yellow top optima battery, and the car was fine. He also said when either one of battery or alternator goes wrong, the other goes wrong too. Does anyone know if my alternator could of gotten messed up during the time i had troubles with the battery?

About two days ago, i had to transport some stuff, so i take my system out. and im driving, and when im at idle, i notice the rpm once in a while dips down and up. I got really frustrated because all this time im thinking its the subs that are doing this. So im there trying to figure it out, and i notice when i idle, my fans turn on, and thats exactly when the rpm dips low and then up. Then when i use my power windows, when i press the brake peddle i notice it does the same. So it seems like everytime i use anything electrical its doing that. I was doing some research, and i read that its normal for the rpm to dip a bit low when something electrical is used such as the power window. But my problem is that I am already idling at low rps already (between 400-500) , and when it dips low, it goes very low, almost close to Zero, which worries me.

Any ideas guys, what the problem can be?

Any advise will be appreciated. Thanks.

 

Are you sure your idle is not 900-950rpm? The first thick line is 0. The next one few hairlines away, thinner one is 500rpm mark. Then you have a bigger/normal gap from 500rpm to 1000rpm.

If you were idling at 400rpm, I assure you your mechanic, friends etc and even you would have noticed a problem. Idling at such low rpm starts shakin the car and its not pleasant. So ill just assume you thought the thin line was 0 and you are actually idling properly.

About your system, how much wattage does it consume and what farad capacitor did you get?

Also when battery/alternator dies doesn't mean the other one will go soon. You can check your battery voltage, if its around 13.4v then your alternator is still good.

Reason for your idle to drop when using anything electrical is simple. Your alternator is making a constant power, but once you use anything electrical, it requires more power, so it gets a bigger load putting more force on the crank pulley...slowing down the engine and then your iac valve compensating and rev matching to proper idle level.

Now your rpms dropping once you push on the brake pedal, its usually a sign of master cylinder wearing out, but if its minor, you shouldn't worry. Next time on a light, try pushing on the brake pedal, it should go I believe 2/3rds of the way, that's with you gripping into the wheel and pushing on the pedal HARD.

If the car tends to rev up/down by itself, few things could help/fix the problem. If the fluctuation in revs is small it could be caused by old gunky coolant/iac valve clogging up. If it drops drastically, then it could be many things from fuel supply/injection to ignition.

Hope this helps, post back if you have any more questions.

 

I'm pretty sure the first thick line is 400 or 500 not 0rpm.. So being 1 or 2 small lines above that is fine..

Scrid3r is correct about the alternator.

 

Hey, Thanks alot for the post Scrid3r. Okai, so i am not idling at 400, i am idling inbetween the 2nd line (500rpm) and the 1000 rpm. So i would say about 700-750. Thats normal right?
When I was coming home and saw that the rpm dropped to Zero, it was literary at zero, at the lowest line possible. I know that it is zero because when the car is off, that is where the rpm meter is. Nizmo suggested that it might be a bad cluster. Any opinions on that?

I have a Rockford Fosgate P3 putting out 500 rms, and the cap is 2.5 farad

The voltage read on the cap reads between 13.5 and 14.3.

Since the Iac Valve is suppost to rev match, do you think my Iac valve needs cleaning or is defective? because my cusin has an integra aswell, and his never drops as much as mine does. His does drop but barely anything. Mine, it drops enough for me to notice it, atleast 3-5 lines lower.

When I press my brake pedal, it does drop alot, i would say its not minor. It drops about half way inbetween the rpm at idle and zero. Is it costly to replace the Master Cylinder?

It used to rev up and high, when I first got the swap. But I was advised by the mechanic that I have to get the coolant to flow, and it will eventually stop. And it has. It doesnt rev up and down anymore.

Again, thanks guys for your opinions /advice

 

it could be the cluster acting up since it doesnt do it all the time...your car should be idleing around 700-850 rpm...but scrid3r got it mainly covered.

 

The reason for rpms to drop when applying brake is because the master brake cylinder uses vacuum, same vacuum system as your intake manifold. So if it leaks you see the consequences in idle. Your iac valve is fine as long as it bumps back up and correct the idle.

Also a simple thing to check are ground terminals on the battery and chasis. Its a simple thing but may cause quite the few problems in idle and overall performance.