Got a rough idle/poor start? Read this!

[mike65]

This is from the benzworld fourms and its required reading if your petrol powered Merc is not starting and running smoothly.

http://forums.mbnz.org/forums/forums/thread-view.asp?tid=1183524&posts=17&fid=14

It worked a treat for me.

Mike.

 

[mike65]

Bumpity-bump!

Mike.

 

[Jamesnel]

Hey Mike,

Don't suppose you'd be able to translate that into English would you?! What exactly is a 'Butterfly'? Would my 2.3-16v have one?

Thanks,

James

 

[mike65]

The butterfly is buried at the bottom of the throttle body (the bit your air box sits on) if you push down the flap at the top and shine a torch in
you will see the butterfly flap (proberly rather grimy) this pivots when you push the accelorater down or tweak the throttle cable at the engine end.

This is not from a Merc but it shows what to look for.

http://www.markl.f9.co.uk/misc/pulsar/throttle/tn_port4.jpg

Mike.

 

[Brensbenz]

Hey Mike,

Although running well, I thought I’d take a look at the butterfly and, sure enough, it was gungy. I cleaned it off with meths on a cloth, re-assembled, started it up and the engine ran fine for a few minutes then started to rock and roll in the engine bay. The BAS / ASR light came on and stayed on. I allowed the engine to cool off and re-tried. Same again! As soon as it comes near to normal temperature, the engine dances and the BAS / ASR light appears. Any ideas? Does this sound like a faulty Air Mass Meter? BTW, 2 litre petrol engine, 1999, not Kompressor.

Thanks,
Brensbenz

 

[teky]

other components to consider MAF/MAP sensor which ever one is fitted might need a spary clean out with carb or break cleaner spray (if map sensor} check the vacuum pipe is not split or disconnected, coolant temp sensor the colder is is the higer the resistance should read useing a multimeter to determin that

 

[mike65]

Although running well, I thought I’d take a look at the butterfly and, sure enough, it was gungy. I cleaned it off with meths on a cloth, re-assembled, started it up and the engine ran fine for a few minutes then started to rock and roll in the engine bay. The BAS / ASR light came on and stayed on. I allowed the engine to cool off and re-tried. Same again!

Oh dear now I feel guilty...

Mike.

 

[Brensbenz]

Teky,
Thanks for swift response. I have a background in electronics but not auto-electronics! When you say MAF/MAP sensor, is this what Haynes calls the Air Mass Meter – buried in the air feed between air filter and throttle body? If not, where is MAF / MAP sensor? After cleaning the butterfly, I checked spark plug connections so the air feed containing the Air Mass Meter was disturbed. I didn’t touch anything else – honest! Which vacuum pipe do you mean?

Mike,
Don’t feel bad – your good advice + my clumsy hands = problem,

Thanks,
Brensbenz

 

[Brensbenz]

Guys,

Don’t know if this will help to get a diagnosis but………..I just did a few miles on quiet country roads. Car ran very well, throttle was responsive, temp gauge at 80 degC, no warning lights but just a hint of jerky gear-changes, although I’m pretty sure this is just my paranoia! Parked for a few moments with engine running and revs immediately began to hunt between about 900 and 1,300. Temp gauge went to about 85 degC when the car began to vibrate, BAS / ASR light came on, revs all over the place. Panic, ignition off, phoned for a lift home in Japanese car!
This afternoon, when I first saw this problem, I noticed the engine cooling fan came on even though the engine temp hadn’t reached its normal 80 degC. All suggestions gratefully received,

Brensbenz.

 

[Brensbenz]

Hey Guys,

More info - when parked with engine running, as soon as I engage Neutral the revs start to hunt and then we “Come Dancing” again. However, if I keep it in Drive, the engine behaves itself for a few minutes before all hell breaks loose. To the Dealer – his computer reckons the Air Mass Meter is OK but electronics on throttle body have a fatal fault. The electronics can’t be repaired or replaced – must get a complete throttle body! None in stock.
On the way home, dawdling behind a caravan, the engine rock and roll started, the BAS / ASR light came on, I lost power – it was difficult to go more than 40 MPH, and then, most worryingly, the braking system seemed to loose power. I pulled over, ignition off for a few minutes, restarted and made it home without much difficulty.
Is the dealer talking “shoemakers”? If I avoid city traffic, is it safe to drive as is? Besides fuel economy, would I damage the cat con or other components?

Brensbenz.

 

[mike65]

Bren,

Was your car running well before your checked and cleaned inside the throttle? I really can't belive a good wipe round will be have done anything to damage the electrics (bear in mind your throttle body is proberly different to mine). If I were you I'd post your symptoms at the other benz foums and with the info you get back then get in touch with a fuel injection specialist.

Mike.

 

[Brensbenz]

Hey Mike,

Yes, car was fine before clean-up. It’s probably just a huge coincidence or maybe static from my hands, or cloth. Looks like today’s lesson is “if it ain’t broke, don’t fix it”.
I thought this was THE forum for best advice! What other forums do you suggest?

Brensbenz.

 

[mike65]

Hey Mike,

Looks like today’s lesson is “if it ain’t broke, don’t fix it”.

I was thinking of saying that a few days back but decided it might be best not to!

I thought this was THE forum for best advice! What other forums do you suggest?
Brensbenz.

There are two other major boards - http://www.mercedesshop.com/shopforum/ and http://forums.mbnz.org/forums/

Mike.

 

[talbir]

Brensbenz,

When cleaning the butterfly, what did you dismantle ?

Did you at any point detach the throttle switch from the throttle body ?

If so, then this needs to be 'matched' up again to the throttle body, which can be only done using a hand-held computer.


I'd double check that allelectrical looms in that region are connected correctly.

 

[Brensbenz]

Talbir,

Thanks for reply. Throttle switch???
I removed the butterfly, i.e. the metal disc, to clean both sides. Before removal, I noted that two dimples on the disc determined its "left / right" position so, after cleaning, I put it back to the same location (I think). There is some space for "forward / back" movement of the disc. Is it possible that, if the disc was too far forward or back, I'd get these results?
No other parts removed from throttle body,

Brensbenz.

 

[panason1c]

Just a long shot but have you tried disconnecting the battery for 1/2 an hour or so?...apparently, this can clear some problems...fault codes, etc

 

[Brensbenz]

Hey Panason1c,
Thanks for reply. I had considered disconnecting the battery but was concerned about creating more horrors. I saw your post about your SRS light and Martin Bell?s suggestion a couple of months ago. Did you try it? Any?ahem...consequences with windows, security system, other warning lights, etc.?
Brensbenz.

 

[panason1c]

Hi Brensbenz, From the problems you are having now i think you cant make things much worse by trying the battery disconnection route.
Good luck.


Regarding a previous post of mine.... i was only enquiring as to were there any points to watch out for on battery disconnection/connection,.. it seems the answer is 'no'