E36 Rough Idling and Auto Rebound

[BMW2007]

Dear Sifu & Bro, My e36 328i is having rough idling when cold start and the car is rocking like washing machine with RPM fluctuate up and down. However the shaking will be gone and stabilize immediately after accelerate rev up the RPM to 1.5~2K then release immediately. Car running smooth without rough when shifting to D, however noticed that the rpm will be "rebound" back to 1.5K when the car slows down to 1K without accelerate. What cause the rpm rebound automatically even without accelerate? It will repeats 3 times before rpm can be really came down to 800 mark while driving in D.Appreciate your advise, thanks.

 

[yat]

hai bro im facing the same prob as u b4, check ur icv sensor conector under the manifold......mybe the socket r dirty or not realy conected...

 

[BMW2007]

thanks bro, what chemical cleanser that uses to clean the ICV if it is dirty?

 

[jeffreyewe]

aiyoo, the symthom came back arr? Please check the ICV and all the vacumm hoses if possible. For the ICV cleaner just get the normal contact point cleaners will do.

 

[BMW2007]

dear bro jeffrey, the symthom still not yet solved lar... what the mechanic did was just took out the throttle butterfly for cleaning and polishing. But at least can feel the 328 power now after cleaning the butterfly but the rough idling still there.. i called the mechanic last week, he said the throttle butterfly is not in good condition wow.. i just dont understand why he didn't clean the ICV on that day, make it a double work now..

I will ask another mechanic to clean the ICV and O2 as well. thanks

 

[yat]

bro u can use any cfc product.....yes... check ur hoses to.....my 325 all the ruber hoses chnge to new one...even bocor sikit pn the idle can be bad..

 

[yat]

anway ur location?

 

[ersalle]

Hehehe this fault sounds very familiar, Check your crankcase ventilation oil/separator pressure regulating valve.The diaphragm inside might be broken or body crack and cause air leaking. Symptoms unstable at idling after revving.

 

[BMW2007]

I have done the Throttle body + ICV + Manifold cleaning + replaced Oil pressure/separator valve lately, this has solved the engine vibration at idling.
Test drive the car, the rpm still rebounding when pedal release for slowly dropping to rpm 1000, it will auto rebound to 1500 then slowly came down again to 1000. What could be the possible cause?

The engine rpm at idling just slightly high at 850 +/-, so I asked the mechanic to lower down it to ~650 by adjusting the throttle body, however rpm rebounding issue still there. It is even worst now when the aircon kick in, the rpm will be dropped to 500 or so. Sometimes, the engine oil indication light is also On and then Off when the rpm is too low (when aircon kick in and break is pressed).

Plug in the computer diagnose, the error code 25 still there (O2 sensor 1, cylinder 123), could it be O2 caused all these or something else?

Any idea? thanks

 

[John_Smith]

Check vacuum hoses. Spoilt O2 sensor will only make your fuel consumption goes worst.
Do you have air mass error code?

 

[BMW2007]

will get the mechanic to check thru the hoses again..
air mass is okay, no error code (it was changed last year). TQ

 

[ersalle]

Ahaaaa! Take note, O2 sensor faulty could also cause errartic idling. And also BMW2007, the rpm should be around 650rpm at idle, aircon kicks in it will bumps up and settle around 750rpm. Actually the idle cannot be adjusted, because the ECU will automatically adjust the ICV to the suitable rpm no matter how you adjust the throttle body housing butterfly valve. This is not carburetor idle adjustment hehehe

 

[BMW2007]

Exactly what my mechanic told me, the rpm should be controlling by ECU and not like the carburretor car.
Somehow the idling rpm can be "slightly" lower down or raise up by adjusting the throttle butterfly.

When the engine is warmed up and gear is engaged, the rpm dropped too much when the aircon kick in.
not sure what caused this..