Rpm Goes Down When Accelerating

gayanW · June 15, 2012

Hello everybody.

i'm driving a kia Rio 2001. I've experienced a rather unusual mechanical problem. i'm just a average vehicle user with limited technical knowledge. perhaps the experts here would be able to help me out with this.

OK this is what happens. all of a sudden i find it difficult to accelerate. i need to push the gas pedal really hard to get the RPM up. This happens only when vehicle is run for sometime, probably after 15-20 Kms. When the vehicle slows down due to traffic, it's hard to pickup the back again cos RPM goes down a bit and then accelerates. it's like the engine is slow to recognize the acceleration through the gas pedal. ( Idle RPM slows down, and engine may even stop in a worse cases). This improves when the car is stopped for a while. and again appears when driven for a long distance ( most of the time). Plus from time to time i get Check Engine indication but this issuue may not happen every-time the check engine comes up. so it's kind of a dilemma. ( i tried to do a scan on check engine, but couldn't detect anything)

Greatly appreciate your contribution to understand this problem.

Thanks!

MasterDon · June 15, 2012

Check if the throttle position sensor is faulty.

hatharasinghe · June 19, 2012

is this auto or manual and all the time your AC is ON or OFF.

Edited June 19, 2012 by hatharasinghe

The Don · June 19, 2012

So basically the car tries to stall before it accelerates when put under load? A couple of things could be at fault here. I would first start by cleaning your throttle body, injectors, idle control valve, air flow sensor and throttle position sensor. See if that gets you anywhere. I had a similar problem and a clean up resolved it. Basically carbon build up and general dust and corrosion tends to skew the readings from sensors and the idle controls valves tend to stick a bit!

Magnum · June 19, 2012

Check your battery terminal/wire, sometime back my cousin had a similar issue in his CR41, it had poor pulling power and it gave trouble going up hills, once he tightened the terminals it was fine

MkX · June 19, 2012

AFAIK you can read CE light history also. So if you don't have CE-light on stil you should be able to find out what sensor gave the error message. As MD said if the throttle position sensor has a fault it will drop rpm (cut off fuel) even if you are accelerating.

jami · June 19, 2012

i got a problem similar to this. rpm goes down and stopped the engine while running. when it start rpm goes around 1000 and suddenly drop to 500 and again up to 1000, this is happen at the idle position. what is the issue??

The Don · June 19, 2012

On 6/19/2012 at 10:34 AM, jami said:

i got a problem similar to this. rpm goes down and stopped the engine while running. when it start rpm goes around 1000 and suddenly drop to 500 and again up to 1000, this is happen at the idle position. what is the issue??

If this happens when the car is idling then your engine is stalling and the stall sensor is cutting in and increasing rpm to try to keep the engine going hence the sudden fluctuations in rpm. Usually the issue is the idle control solenoid or valve if your car has one but many other things can cause the same issue.

jami · June 20, 2012

On 6/19/2012 at 11:58 AM, The Don said:

If this happens when the car is idling then your engine is stalling and the stall sensor is cutting in and increasing rpm to try to keep the engine going hence the sudden fluctuations in rpm. Usually the issue is the idle control solenoid or valve if your car has one but many other things can cause the same issue.

thanks. ill check on this

gayanW · June 22, 2012

On 6/19/2012 at 3:29 AM, hatharasinghe said:

is this auto or manual and all the time your AC is ON or OFF.

its automatic. AC is ON when this happens.

gayanW · June 23, 2012

On 6/19/2012 at 8:21 AM, The Don said:

So basically the car tries to stall before it accelerates when put under load? A couple of things could be at fault here. I would first start by cleaning your throttle body, injectors, idle control valve, air flow sensor and throttle position sensor. See if that gets you anywhere. I had a similar problem and a clean up resolved it. Basically carbon build up and general dust and corrosion tends to skew the readings from sensors and the idle controls valves tend to stick a bit!

latest situ on this.... took the car to a paint job.....and when then try to start the car the engine stalls! it was doing ok for few days...this happened only today.

Don....i got throttle body cleaned a month back. plugs are new. maybe should have a check on air flow sensor and ICV

The Don · June 25, 2012

On 6/23/2012 at 5:01 PM, gayanW said:

latest situ on this.... took the car to a paint job.....and when then try to start the car the engine stalls! it was doing ok for few days...this happened only today.

Don....i got throttle body cleaned a month back. plugs are new. maybe should have a check on air flow sensor and ICV

I think the paint guys must have disconnected the battery and in the process reset the ECU. I don't think there is anything particularly wrong with the plugs or throttle body.

Try running for a few days and see if the ECU automatically adjusts itself. Else you should check the map/MAF (air flow) sensor, check for vacuum leaks and of course the ICV. The ICVs unfortunately gets a bit dirty and suffers from carbon clog up so you might need to clean it. There is a particularly known issue with cars that use Mitsubishi made ICVs from the 1990s like Hyundai etc.

SubZero · March 19, 2013

On 6/15/2012 at 5:38 PM, gayanW said:
Hello everybody.
OK this is what happens. all of a sudden i find it difficult to accelerate. i need to push the gas pedal really hard to get the RPM up. This happens only when vehicle is run for sometime, probably after 15-20 Kms. When the vehicle slows down due to traffic, it's hard to pickup the back again cos RPM goes down a bit and then accelerates. it's like the engine is slow to recognize the acceleration through the gas pedal. ( Idle RPM slows down, and engine may even stop in a worse cases). This improves when the car is stopped for a while. and again appears when driven for a long distance ( most of the time). Plus from time to time i get Check Engine indication but this issuue may not happen every-time the check engine comes up. so it's kind of a dilemma. ( i tried to do a scan on check engine, but couldn't detect anything)

Greatly appreciate your contribution to understand this problem.

Thanks!

On 6/19/2012 at 10:34 AM, jami said:
i got a problem similar to this. rpm goes down and stopped the engine while running. when it start rpm goes around 1000 and suddenly drop to 500 and again up to 1000, this is happen at the idle position. what is the issue??

Guys,

My vehicle is having both these issues since about two weeks back. Did an efi tune up and an engine scan. currently running with a fuel system cleaner mixed with petrol. The technician said there are no error codes, but the problem still persists.

Took to another place last week and I saw there was an error code for throttle valve position. He tried to reset the ECU with the scanner but couldn't. He did a manual reset which I think was not successful.

I replaced the battery before any of this happened and the battery also shows being under charged( battery is only one and a half months old).

I'm looking for a good place to do a full engine scan and a reset since according to your earlier replies it looks like to be errors with the throttle position and the idle control.

Any suggestions of a good place to do an engine scan pls?

SubZero · March 21, 2013

Any one to recommend a place...?

MkX · March 22, 2013

On 3/19/2013 at 7:38 AM, SubZero said:
Guys,
My vehicle is having both these issues since about two weeks back. Did an efi tune up and an engine scan. currently running with a fuel system cleaner mixed with petrol. The technician said there are no error codes, but the problem still persists.

Took to another place last week and I saw there was an error code for throttle valve position. He tried to reset the ECU with the scanner but couldn't. He did a manual reset which I think was not successful.

I replaced the battery before any of this happened and the battery also shows being under charged( battery is only one and a half months old).

I'm looking for a good place to do a full engine scan and a reset since according to your earlier replies it looks like to be errors with the throttle position and the idle control.

Any suggestions of a good place to do an engine scan pls?

What is your car? I think problem with a sensor related to the fuel system. Give some more information.

SubZero · March 22, 2013

Hello MkX. The vehicle is a manual Yaris.

First it appeared when I was overtaking a vehicle. The engine slowed down mid way of accelerating. Then after a while in the same journey the engine started to miss and I had to pull over. The engine was responding ok when I pressed the accelerator when stationary, but on the move the engine speed didn't go up consistent with the accelerator.

It was OK on the next day I drove in it. But on another day in the traffic this appeared again and the problem was worse. Even when stationary the engine didn't speed up. Even in the idle the engine speed dropped and a few times, halted.

After the two scans and the tune up, the problem is more or less limited to the idle issue(now after slowing down to about 400 rpm, the engine suddenly speeds up by itself) but some times when running the acceleration is not smooth. Its a little difficult to balance the clutch because of the difference in the response to the pressing of the acceleration peddle.

Edited March 22, 2013 by SubZero

MkX · March 22, 2013

These are the exact symptoms of TPS failure I had long time ago. Also check the vehicle speed sensor & ideal air control valve.

SubZero · March 22, 2013

Thank you MkX. Any place you can recommend to get it sorted?

Charith H Jayasinghe · July 20, 2013

On 6/19/2012 at 8:21 AM, The Don said:
So basically the car tries to stall before it accelerates when put under load? A couple of things could be at fault here. I would first start by cleaning your throttle body, injectors, idle control valve, air flow sensor and throttle position sensor. See if that gets you anywhere. I had a similar problem and a clean up resolved it. Basically carbon build up and general dust and corrosion tends to skew the readings from sensors and the idle controls valves tend to stick a bit!

Oh I had the similar issues. Did the same as above and corrected after I bought the car. Thanks for this. Didn't have authentication to post those days.

Grid · January 13, 2014

quick fix works on some older automatics .... just before accelerating switch off the AC and accelerate then switch it back on..

( normally when the AC is on it reduces HP by about 3-4 on automatic cars )

Rumesh88 · January 13, 2014

On 1/13/2014 at 10:31 AM, Grid said:
quick fix works on some older automatics .... just before accelerating switch off the AC and accelerate then switch it back on..
( normally when the AC is on it reduces HP by about 3-4 on automatic cars )

That's not a fix my dear but an ad hoc measure to circumvent the real issue! It is a 6-month old thread anyway?