2000 Honda Accord engine RPM fluctuation

Hi iamfurqan,

A lot of things can jam up when not used over a period of time. There are 2 things likely to cause this problem.

1. Throttle position sensor. Check the TPS voltage at fully closed (0.5v) and open (4.5 v) throttle and confirm voltage increases smoothly with acceleration. Some slight difference in reading is acceptable.

2. The IAC valve is stuck.

Is the idling speed normal? Cold start more than 1500 rpm and lowers to 700 when engine operating temp is attained?

thx for the reply.i
yes idle RPM ok. if i left car running on idle it kept on running as long as not being switched off. and normal idle RPM are 700. kindly would you tell me what is IAC valve.

Hi iamfurqan,

Intake Air Control valve. It is the unit attached to the lower part of the throttle body with 2 coolant hoses passing through it.

Idle rpm = 700, what about with A/C on and also when engine is cold?

hi khlow;
thanks for reply. idle RPM are 700 and when puting on AC. it droped around 550-600. but still it kept runing.

Hi iamfurqan,

Idle rpm should not drop when AC is operated so the IAC is at fault. You need to clean it and the throttle body.

hi sir,
i had checked my car from honda and they also revieled the same thing you had mentioned. they are asking to replace IAC valve and throttle body.
kindly can you tell me it is whole throttle body need to be changed or it is throttle position sensor which
actualy have to be changed.
does idle control valve or intack control valve is same thing.

Hi iamfurqan,

The throttle body comes as a whole unit with the IAC and throttle body. It is not going to be cheap.

If the check engine light is not showing, I would recommend cleaning the IAC.

Get yourself a can of carb cleaner. Remove the intake hose and spray into all the holes you have inside the throttle body. Wait a while and start engine, spray again if it is very dirty. Remember to push the throttle valve open to get to the inside. engine would stall if you spray too much, it is ok, just try to rev up a bit to keep it going.

Get a second opinion, might save you some $.

i have replaced my throttle body and IAC valve. my car was running very smooth for few days almost 100Km. then one morning when i started my car it started with RPM at 2000 after 3 or 4 minutes it started fluctuating RPM between 2000 to 3000RPM. moment i put my car in drive things become ok. after couple of days now again its the same as arlear. it is running ok at idle but when i put it in drive there is fluctuation in RPM. there is too much fluctuation. when i am driving sudenly RPM start falling then again goes up like i am driving at 100Km speed it start droping to 60Km then sudenly it will start increasing to 100 speed. couple of times it stall at red lights and it is giving very jurking start when i accelerate from stop. pl tell me now what to do.

Hi iamfurqan,

Check the radiator coolant level and see if coolant hoses to IAC are clogged.

i have checked radiator coolent level, it is ok and also IAC hoses are not cloged. my mechanic is insisting to replace IAC again since it was running ok for first few days after replacement.
i checked my old throttle body with multimeter there was smooth variation from 0.8 to 4.6 kohm and there was no continuity at IAC . is it means that my throttle body was ok only IAC was bad.

Yes, TPS is ok, IAC is bad if there is no continuity.

It is possible for the replacement IAC to be bad, was it a used or new unit thet you replace?

yes that replaced IAC was used. later in the day i had checked voltages at IAC, MAF sensor and TPS all were ok giving battery voltages. finally i had replaced thermostate and since then every thing is ok i have driven 20Km and through out running it was perfactly smooth.
keep in mind the thermostat i have replaced is now UAE gulf spacificationi earlleir thermostat was amarican spacification since my car is imported from USA. what do you think that might have been the problem. temprature here is most of the time very hot.

Yes, the thermostat can cause the surging if the rating is different.

That was the reason I reminded you to check the coolant level and hoses for clogging.

ahh! once again it is behaving same after running 50Km.
Now this time i have just reset the computer by removing -ve terminal of battery, and again it is running smooth. so it looks like when ever i am reseting the computer it is becoming ok for 50 to 80Km and again start behaving same. so what do you think now.

What is the idling speed when it is running smooth?

Any losses in coolant level in the radiator?

The IAC seems faulty but then why should resetting cause a temporary reprieve?

idle seed is almost 800 and once i switch on A/C it goes about 1000 for lest then second and comes down to 800 again. and no loss of lequid at all.
tell me one thing is it posible my ECU is giving some frequesncy to IAC as per requirement of load and due to malfunction of ECU its feeding frequency to IAC changes or start fluctuating and when we requirement is reset ECU it becomes ok till again due to some internal fualt it start surging again. what makes me belive IAC is working on frequency not opening of gate as per rquirement of load is that when i checked voltages after switching on was 12volts on both terminals of input plug to IAC.

IAC receives power from ignition switch and the ECM will ground the other two terminals depending on engine operating temperature and conditions with various input from other sensors to control the idling speed.

The fluctuation in idling speed when AC is turned on points to a fault in the IAC or ECM.

Please can you tell me if i can check my ECM weither it ok or not.
So is it posible to install ECM direct from scrap for the same modle or i have to reprogram it first for my car. if i have to reprogram how can i do it.
and also can you tell me the part number of ECM, my VIN # is 1HGCG6652YA141254
Once again i am thankful to you for your time and support to me.

No reprograming is required unless equipped with immobilizer system.

You need to check the ECM part # on your vehicle and get the same from the scrap yard.

I would try replacing the IAC first, more likely to be the source.

at last while looking around for another IAC in scrap, i met with mechanic he asured me he can fix the problem. in one day he fixed it but he is not willing to tell me what he had done to my vehical but car is running very smooth. i dont know what he had done and also i dont know weither i should be happy more or worry more. cause i dont know what he had done. one thing i had noticed after ward i had never noticed earlier, when car is in drive and AC is one after every 60sec or so with comprassor turning on sound RPM goes to 1000 and then imidiatly come back to 800. is it ok.
once again thanks for your support.

If the CEL is not showing and no other noticeable problems showing, I guess there is nothing to worry about.

My guess is that he has done some adjustment to the IAC.
The problem with some people is the they worry someone would steal their secret.
Maybe they would rather bring it to the grave let others know how they did it.

at last i have a clue what he had done. i was inspecting my engine for any clue what that mechanic had done when i noticed that my oxygen sensor was actualy not connected rather it was engaged so that no body would notice it is disconnected. i imidiatly called that mechanic and ask if i should connect it, he forcefully recomend me to not connect it back otherwise my car will start bevaving same like earlier. he said that sensor was bad and he had made arrangement and reprogrammed the computer to ignore it thats why car is running ok know. he is still not telling me any thing else. so what do you think, what actualy he had done. kindly tell me the roll of oxygen sensor in this problem.
thanks once again.

Does the Check Engine Light show for 2 seconds during initial ignition On?

Honda PCM are non programmable unless he has replaced the chips. I don't understand what he is bs about.

Get a scan done and see if you can find any error codes, don't reconnect the O2 sensor first.

The role of the Snitcher ( Oxygen Sensor ) is like a heart monitor for the engine's air/fuel mixed when in the closed loop operation. When disconnected it will have a low reading and computer will constantly adjust for fuel making it run rich.

HOW IT WORKS

The O2 sensor works like a miniature generator and produces its own voltage when it gets hot. Inside the vented cover on the end of the sensor that screws into the exhaust manifold is a zirconium ceramic bulb. The bulb is coated on the outside with a porous layer of platinum. Inside the bulb are two strips of platinum that serve as electrodes or contacts.

The outside of the bulb is exposed to the hot gases in the exhaust while the inside of the bulb is vented internally through the sensor body to the outside atmosphere. Older style oxygen sensors actually have a small hole in the body shell so air can enter the sensor, but newer style O2 sensors "breathe" through their wire connectors and have no vent hole. It is hard to believe, but the tiny amount of space between the insulation and wire provides enough room for air to seep into the sensor (for this reason, grease should never be used on O2 sensor connectors because it can block the flow of air). Venting the sensor through the wires rather than with a hole in the body reduces the risk of dirt or water contamination that could foul the sensor from the inside and cause it to fail.

The difference in oxygen levels between the exhaust and outside air within the sensor causes voltage to flow through the ceramic bulb. The greater the difference, the higher the voltage reading.

An oxygen sensor will typically generate up to about 0.9 volts when the fuel mixture is rich and there is little unburned oxygen in the exhaust. When the mixture is lean, the sensor output voltage will drop down to about 0.2 volts or less. When the air/fuel mixture is balanced or at the equilibrium point of about 14.7 to 1, the sensor will read around .45 volts.

hi rasmataz,
thanks for your information regarding O2 sensor. can you suggest me the roll of it in my case history. how come a bad sensor have been bothering me so much my car was running with so much fluctuation that it was almost imposible to drive it. now mechanic has disconnected my O2 sensor and it is running ok and he is insisting my car will consume less fuel and i have also noticed it is consuming lot less fuel now.

Sound like the problem is a lean mixture and computer compensating by throwing fuel at it. When an oxygen sensor is disconnected/contaminated/out of range the air/fuel will be rich at all times.

You need to test the voltage to the oxygen sensor-could be a wiring problem or computer