Engine shaking when start, car rpm jumping up & down

[azeL_Inc]

Something weird happen to my car yesterday & today, n i think it still persists, no error light whatsoever.Symptoms: When i start the car, the car shaking really bad, coz the engine like dying off and on, RPM jumping from .6k to 1.5k... (my normal idle RPM is 8k).And it only happens when i first start the car, doesnt matter the car is hot or not (i mean it doesnt only happens during morning cold start). What is the weirdest to me is that, during that period, sometimes like there s someone pressing the gas, coz the rpm went up to 2k for few seconds, on its own. weird huh. it happens for 1-5 mins, if i force the car to move with that condition, engine goes back normal.Btw, i just picked the car from workshop 3 days ago, previously, I left the car at a workshop for some minor repair at the front, replace bumper, hood & paint job. The car wasnt moving for 3-4 months. Just replaced the engine mounting.Any idea on the possible cause? Dont think misfire also, coz after around 10 mins, it normal back, but the shaking is reallllly bad.it s N42 btw

 

[anaksarawak]

Guess ... I mean "Guess" or "Assumed" its caused by leaking vacuum hose. Please have them checked as they normally will crack due to aging.

 

[azeL_Inc]

Thanks anaksarawak.. you ve made me read more on vacuum hose leak, n led me to the video

http://www.youtube.com/watch?v=W2s-qcT7tjU

it is almost the same symptoms as mine. anyway he solved it by replacing MAF.. would look into it as well...i had no clue before. thx a bunch!

 

[jarance]

try to start the car with the maf cable disconnect and see what happen,

 

[azeL_Inc]

try to start the car with the maf cable disconnect and see what happen,

That i can do, will do it tmrw, coz now raining.. what should i expect if the MAF is the culprit?

 

[jarance]

That i can do, will do it tmrw, coz now raining.. what should i expect if the MAF is the culprit?

if the idling speed is stable when the maf is disconnect during cold start, then the problem lies with the maf.

you can try to clean the maf with crc maf cleaner before changing to new one.

 

[koreng]

Had the same problem. Could be your vacum hose nor Air flow hose. Try disconnect your MAF first for troubleshooting, My top guess would be the vacuum hose. hehe

 

[azeL_Inc]

have yet to try the disconnect MAF method! it s rainy everyday over here, hence, no window to do it, car parked under the sun, no porch.
so u solved ur vacum hose, by replacing it?

edit: additional info, found some whitish sludge at coolant tank cap. could this be related? got scared after reading the thread below, when related to ATF etc. hope it s not related!

http://www.bmwclubmalaysia.com/foru...-milkly-sludge-at-radiator-cap-E46-328i/page4

 

[azeL_Inc]

Finally got the time to do the stuff. Well, it was the first time i ever unscrew anything under the hood. Hehe
Actually, i bought new air filter, so while checking the MAF that Jarance suggested, I intent to change the air filter as well. (bought the air filter from Bomin Auto for RM55)
Unscrew the cover engine and manage to take out the "Intake Silencer". While doing that, i saw a small pipe going into the intake silencer is not plugged! Plugged that in, start the engine and the engine no more jumping on off!!

But i found the engine is still unusual, so since i d already dirtied my hands, i decided to go on, check the MAF and change the air filter. THen i saw the "rubber boot with resonator" (according to realoem) has a hole on it, due to friction with the belting system. Dont think that is good since the name suggest something that i think cant tolerate leakage, haha.

Item no.5 in the diagram.
http://realoem.com/bmw/diagrams/m/u/286.png

Stop work, gonna go and buy myself a new "rubber boot with resonator" and will complete the work.

*kinda proud of myself, and to my surprise, i actually enjoyed myself this evening. LoL. Thanks for somehow motivating me to DIY!

 

[anaksarawak]

Finally got the time to do the stuff. Well, it was the first time i ever unscrew anything under the hood. Hehe
Actually, i bought new air filter, so while checking the MAF that Jarance suggested, I intent to change the air filter as well. (bought the air filter from Bomin Auto for RM55)
Unscrew the cover engine and manage to take out the "Intake Silencer". While doing that, i saw a small pipe going into the intake silencer is not plugged! Plugged that in, start the engine and the engine no more jumping on off!!

But i found the engine is still unusual, so since i d already dirtied my hands, i decided to go on, check the MAF and change the air filter. THen i saw the "rubber boot with resonator" (according to realoem) has a hole on it, due to friction with the belting system. Dont think that is good since the name suggest something that i think cant tolerate leakage, haha.

Item no.5 in the diagram.
http://realoem.com/bmw/diagrams/m/u/286.png

Stop work, gonna go and buy myself a new "rubber boot with resonator" and will complete the work.

*kinda proud of myself, and to my surprise, i actually enjoyed myself this evening. LoL. Thanks for somehow motivating me to DIY!

Superb!! Next time lets DIY together.

 

[wingzee]

Just realized my car has the same symptom. Erractic rpm only during cold start. But only from the range of 900-1k rpm. Shall check on the vacuum hoses.

 

[azeL_Inc]

this is the pic of the rubber boot with resonance thing that i m gonna replace. See the hole in that thing? I think that might cause the unstable engine. Quoted Rm170 for that thing at Bavarian Auto. Changed the filter (never been changed, the colour is super black, and just bought CRC MAF Cleaner for Rm39 from Brothers Ampang). Hoping for significant improvement after this! Else, demotivated to DIY again. haha

 

[jarance]

You can temporary tape up and seal the hole with many layer of masking tape and check whether the problem is solved.

As for me, I will change the damaged part. Also check why the moving part is causing the cut in the resonator as the problem will
occurred again if not address.

 

[azeL_Inc]

Was busy and didnt get the chance to update.

Update: I changed the rubber boot with resonance (bought from BA segambut), while i am at it, i changed the air filter (never been changed since my 5 years of ownership), cleaned the MAF using CRC MAF Cleaner.

To my surprise, i got a very good fuel consumption now (about 11km/liter, good? haha..previously worse), smoother engine (minimal shaking when idle). more importantly, it s a DIY. the satisfaction is priceless.

 

[koreng]

Did you notice anything on the sudden drop of RPM from 3rd gear to 2nd gear?

 

[aidilj]

Yup the N42 (ME9 DME) will rev the engine up and down during idle if there is a leak after the MAF. During cold start the engine vibration would be worse because it depends solely on the input from MAF and not O2 sensor, and air that gets into the engine is much more than metered by MAF so the engine is running lean.

After the engine (O2 sensor) is warmed up, it will start to use O2 sensor reading and will be able to trim the fuel accordingly. A conflict between metered air and air fuel ratio will cause the DME to rev the engine up and down. Cheers

 

[koreng]

Yup the N42 (ME9 DME) will rev the engine up and down during idle if there is a leak after the MAF. During cold start the engine vibration would be worse because it depends solely on the input from MAF and not O2 sensor, and air that gets into the engine is much more than metered by MAF so the engine is running lean.

After the engine (O2 sensor) is warmed up, it will start to use O2 sensor reading and will be able to trim the fuel accordingly. A conflict between metered air and air fuel ratio will cause the DME to rev the engine up and down. Cheers

I still dont get it. he he. It has nothing to do with the sudden gear drop (RPM) from 3rd gear to 2nd gear as you slow down?

 

[ichi82]

Yup the N42 (ME9 DME) will rev the engine up and down during idle if there is a leak after the MAF. During cold start the engine vibration would be worse because it depends solely on the input from MAF and not O2 sensor, and air that gets into the engine is much more than metered by MAF so the engine is running lean.

After the engine (O2 sensor) is warmed up, it will start to use O2 sensor reading and will be able to trim the fuel accordingly. A conflict between metered air and air fuel ratio will cause the DME to rev the engine up and down. Cheers

bro,
can O2 sensor cause smoke to come out. I am currently having this problem. i noticed some kind of irritating smell from the exaust and if i drive or in a commute for a some time smoke starts to come out like a chimney..smoke disappear after a decent acceleration.

 

[krsna86]

Did you notice anything on the sudden drop of RPM from 3rd gear to 2nd gear?

I get this some times, suprisingly only happens on RON97 fuel RON95 no problem. Any ideas why? My mech is also puzzled and the only reason he could give is the ECU is adjusting to the octane levels.

 

[sharizat]

Something weird happen to my car yesterday & today, n i think it still persists, no error light whatsoever.

Symptoms:
When i start the car, the car shaking really bad, coz the engine like dying off and on, RPM jumping from .6k to 1.5k... (my normal idle RPM is 8k).
And it only happens when i first start the car, doesnt matter the car is hot or not (i mean it doesnt only happens during morning cold start). What is the weirdest to me is that, during that period, sometimes like there s someone pressing the gas, coz the rpm went up to 2k for few seconds, on its own. weird huh. it happens for 1-5 mins, if i force the car to move with that condition, engine goes back normal.

Btw, i just picked the car from workshop 3 days ago, previously, I left the car at a workshop for some minor repair at the front, replace bumper, hood & paint job. The car wasnt moving for 3-4 months. Just replaced the engine mounting.

Any idea on the possible cause? Dont think misfire also, coz after around 10 mins, it normal back, but the shaking is reallllly bad.

it s N42 btw

Did u check your throttle body and idle valve sensor and clean them.? Check intake hose and all vacuum . Maybe one of it is the caused. Me still learning the symptoms also :smokin: