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#1: Unstable idle. Author: theduke,

Posted: Tue Nov 10, 2009 5:03 pm
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Greetings everyone,

I have an e30 powered by the famous M20b25 powerplant which is the Motronic 1.1 version. It seems that everytime i switch on the A/C, as the compressor kicks in the RPM Lowers down to as low as to 500rpm from a normal 900-1000rpm(A/C off). The problem worsens when the headlights and radio are ON altogether. And as u start to drive, it feels like the engine isn't up to it's optimum potential....another word is - it drags..Which makes me prefer to drive it with the window down most of the time. This is the part where i do not understand why the engine runs much more smoother with the A/C off?

Is this normal?

thanx.

#2: Re: Unstable idle. Author: highwaystar, Location: Kola Lompuer

Posted: Tue Nov 10, 2009 5:58 pm
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Older cars like that hehehehe... check your alternator looks like power output more than input. Battery also part of it. I use Din 75

#3: Re: Unstable idle. Author: theduke,

Posted: Tue Nov 10, 2009 6:22 pm
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highwaystar wrote:

Older cars like that hehehehe... check your alternator looks like power output more than input. Battery also part of it. I use Din 75

thanx for the tip Bro highway*....but,hw to check the alternator?i mean the output & input?care to elaborate?

PLus the radio shuts down on it's own everytime the signal lever is in use. Even the power window goes crazy too sometimes as if there's an insufficient power supllied.

thanx.

#4: Re: Unstable idle. Author: al3dx, Location: Kota Kinabalu, Sabah

Posted: Tue Nov 10, 2009 6:33 pm
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Ah... Then i will agree with Bro. Highwaystar... Please check your alternator and also your battery... Check your main power flow... which means check your Voltage & Amp (current) flow.... Then lastly check for your grounding...
Make sure that all your body surface submits efficient grounding...

#5: Re: Unstable idle. Author: highwaystar, Location: Kola Lompuer

Posted: Tue Nov 10, 2009 7:09 pm
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theduke wrote:

highwaystar wrote:

Older cars like that hehehehe... check your alternator looks like power output more than input. Battery also part of it. I use Din 75

The best way is to use volt/amp meter. Most kedai battery ada. OR DIY,
While car idle, disconnect negative so the car will run solely on your alternator for 5 minutes. If you disconnect and engine mati... alternator charge tak cukup POWER. Good luck

#6: Re: Unstable idle. Author: lempeng7,

Posted: Tue Nov 10, 2009 7:30 pm
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Emmmm...similar case was happened with me before.
After I changed the battery, it seems like all back to normal.
It might be insufficient power supply from battery.

Good Luck!

#7: Re: Unstable idle. Author: theduke,

Posted: Tue Nov 10, 2009 7:36 pm
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aite...will do.thanx guys!..

#8: Re: Unstable idle. Author: boy_mtech, Location: Selangor

Posted: Tue Nov 10, 2009 11:46 pm
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Bro highway.. U r using DIN 75? Wah so big ar? Me only using DIN 55.Now which one is the best and suitable?

Need more time for alternator to recharge la bro if using bigger battery...

#9: Re: Unstable idle. Author: irman, Location: Ampang/KL

Posted: Wed Nov 11, 2009 10:38 am
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me now using DIN 66 for my m20b20 previously used DIN 55

DIN 55 can be use if refer to the battery shop list..
but i think not enough power.. could be for 318 m40.. thks.

#10: Re: Unstable idle. Author: jeembo, Location: Car_Junk

Posted: Wed Nov 11, 2009 11:15 am
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boy_mtech wrote:

Bro highway.. U r using DIN 75? Wah so big ar? Me only using DIN 55.Now which one is the best and suitable?

Need more time for alternator to recharge la bro if using bigger battery...

i've been using DIN55 for my Agong ride for 4 years now...still going strong hehehehe...and plz believe me that i've raped it like nobody business...jump it here and there, left it on the floor...test it on other car..etc..etc...but still it hasn't failed me:) i use Incoe battery.

#11: Re: Unstable idle. Author: highwaystar, Location: Kola Lompuer

Posted: Wed Nov 11, 2009 11:41 am
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dayammmmm, sorry DIN66 Din75 Volvo kakak aku heheheheh. One more thing, Front mount battery WET CELL, rear mount DRY CELL.

#12: Re: Unstable idle. Author: theduke,

Posted: Wed Nov 11, 2009 1:42 pm
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hi guys,thanx for the heads-up..just got back from the mech this evening & had the alternator + battery checked via vlt/ampmetre.he said everything seems to be running fine..now da jalan buntu...adoi...any more ideas sifu2 sekalian??..

thanx..

#13: Re: Unstable idle. Author: highwaystar, Location: Kola Lompuer

Posted: Wed Nov 11, 2009 5:20 pm
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I set my RPM on 1100-1200, switch on Aircond goes to 700-800. Please try to tune your engine (timing). Other than that, banyak lagi contribute to this prob. Air intake kotor, Throttle body, O2 sensor.

Ahh... i think it should be engine coolant temp sensor. Change this first, it should be located around thermostat housing Laughing

#14: Re: Unstable idle. Author: al3dx, Location: Kota Kinabalu, Sabah

Posted: Wed Nov 11, 2009 8:16 pm
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Why not 1st check all your grounding surface... to the body & to the engine... once you've accomplish that and make sure it's perfectly well... then you wont have to worry about grounding distribution... just focus on your main direct wiring...

#15: Re: Unstable idle. Author: theduke,

Posted: Mon Nov 23, 2009 1:21 pm
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"There is a wire that tells the ecu when the aircon compressor is on, this tells the ecu to raise idle to compensate for the extra load. If it's not connected you will get the idle drop. I had the same problem after engine overhaul when they forgot to connect back the wire. Can talk to ah wai at bmworld about it, he will know about this.

I didn't have the other problems you describe with insufficient power, crazy electrics etc so that sounds like another issue, maybe some bad grounds or too many grounding locations. Also how many years old is your battery?"-

This is what i got from a fellow forummer in BMWCM forum.Any of u guys here have any ideas regarding this?

cheers.

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