Strange Problem When letting go of accelerator.

[futron.sim]

I am facing this intermittent problem with my 318is. When I let go of the accelerator, sometimes, the car won't engage engine brake.

Usually, when I let go of acceleration at high RPM (~2K or more), the fuel economy meter will go to 0 and I can feel the car slowing down due to engine brake. But sometimes, the meter won't go to 0, instead it remains around around 2-5L/100KM mark and I don't feel any engine brake at all.

It happens more frequently when I turn on the AC. If AC is off, it seems to function normally (happens only once or twice)

When its idling, the RPM will also hover around 1K RPM mark instead of 850-900PRM mark.

The engine also stalled twice today when I let go of the accelerator. The fuel economy mark jumps to around 15L/100KM and the engine just died.

I am wondering whats wrong with the car. Its it due to faulty throttle position sensor (sening I am still engaging accelerator when I am not) or perhaps something is wrong with my ECU?

 

[centurion]

Re: Strange Problem When letting go of accelerator.

In optimal conditions, the algorithm is like this when you let go accelerator

If engine is running faster than idle speed, ECU will shut down injectors and spark but will still be in active mode.

Reasons:
When you switch on the a/c, the idle treshold is increased. Thus at a high gear, the ECU may not choose to shut the injectors.
Your idle has increased to 1K, there is probably a sensor issue or idle control valve issue but your ECU is working just fine.

To check idle control valve issue, open your engine, listen under the intake manifold, is there a clicking sound? If so, it's dead or dirty. Can clean it using brake cleaner or engine cleaner, but what the heck just get a new one.

 

[futron.sim]

Re: Strange Problem When letting go of accelerator.

Thanks for the explaination. I didn't think of the ICV....

Went to Eng Soon during lunch time to buy a new throttle positioning sensor (since its easy to replace). The problem seems to be gone. Drove the car for around 30mins, no idle problems or engine brake issue even with AC on.

Keeping my fingers cross. Hopefully, its just a faulty throttle sensor.

 

[dpointt]

Re: Strange Problem When letting go of accelerator.

what is a throttle positioning sensor??
how do u get it replaced??

 

[futron.sim]

Re: Strange Problem When letting go of accelerator.

what is a throttle positioning sensor??
how do u get it replaced??

A throttle positioning sensor is one that senses how much the throttle butterfly is opening. If you step more and it detects the butterfly opening more, the ECU will spray more fuel etc to increase engine power.

As for how to get it replaced. I can't exactly describe in words. It would be easier if you refer to your service manual. Its just a connector and 2 screws for my case.

Anyway, its pretty much confirmed that the sensor went busted. My problems are gone after replacing the sensor. Everything is working fine now.

 

[lordfire]

Re: Strange Problem When letting go of accelerator.

when i let go of my accelerator the fuel economy marker sometimes stay at 15L-20L/100km for quite a while. most of the time it will drop steadily to 0. is there a problem brewing somewhere ? sometimes i just want to coast along to the red light but the auto gear seemed to downgear and slow the car down too fast... is that normal too ?

 

[centurion]

Re: Strange Problem When letting go of accelerator.

u wanna coast just put the car to neutral.

 

[lordfire]

Re: Strange Problem When letting go of accelerator.

hmm....thought someone in the forum mentioned not to put to neutral too often as will damage the autogearbox.... also i noticed when set to neutral the rpm is at around 1000 or plus a bit and not normal idle....

 

[phil]

Re: Strange Problem When letting go of accelerator.

just disconnect the sensor, that works too

 

[lordfire]

Re: Strange Problem When letting go of accelerator.

which sensor do u mean ? and where is it located ?