Car behavior at startup - Mercedes Benz SLK Forum

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#1 Old 09-09-2008
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Car behavior at startup

This is just a question for conversation purposes and something I'm curious about.

How does your car behave when you first start it?

Here's what I mean. When I start my SLK for the first time on a day, put it in drive, and take my foot off the brake, it takes off. By that, I mean that it jumps to about 5 mph without me giving it any gas. I need to pay attention to where it is pointed or I could run right into the edge of my garage. If I'm driving around for a bit, stop to run into the store, and come back out, it is different. In this case, it doesn't take off until I give it some gas.

In contrast, I have a 1997 Pontiac Grand Prix. If I haven't started it for a day or two, it doesn't want to go anywhere without me giving it gas. If I just stop for a bit and start it again, it starts to move on its own - but not like the SLK. The whole behavior is opposite of the SLK.

I guess this scenario only applies to the automatic transmission cars.

Surely there must be some logical explanation for this behavior. Does the SLK computer know that it hasn't been running and then feeds it a little gas at startup?
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#2 Old 09-09-2008
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It sounds like the initial rpm is still high when you put in on drive/reverse.

Here's what I habitually do: after starting the car in P, I do not shift the auto transmission to D or R right away. I watch the rpm (whilst enjoying the sound of the engine while SmartTop retracts the roof), it is around 1000rpm the first 30-60 seconds, and it will gradually decrease to around 700-750 rpm (now enjoying the low-pitch barble). I then step on the brake pedal, and move the gear into R (in my case), gradually release pressure on the brake pedal and the car reverses slowly, probably 1-2 mph.

If I let go (almost completely no pressure) of the brakes it will reverse at a higher rate of speed, like 5-7 mph, which is too fast for me. When the engine is warm (90-100 C), the car will move at a slower rate when the gear is engaged but then the idle rpm is close to 500-600.

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#3 Old 09-09-2008
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Interesting. I must admit I've never paid any attention to the RPM when first starting the car. I'll start paying attention to that. I also tend to pull the car out of the garage right away after starting it. That's a habit I got into from my older car. I didn't like the smell of the car fumes getting into the house.

Even though you wait a bit, it sounds like yours takes off pretty quickly if you let it.
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#4 Old 09-09-2008
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....
Even though you wait a bit, it sounds like yours takes off pretty quickly if you let it.
That's right, it still moves at a rate of speed higher than when the engine is at its operating temp.

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#5 Old 09-09-2008
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Eddy's got it right, its just the higher engine RPM's causing the car to jump.

It has a higher startup idle so it can heat up its cat's quickly it means if you put it into a drive mode at that point its gonna kangaroo.

I just do what Eddy does to get around it and it works a treat plus it has about a minute to figure out if it has any faults while its sitting harmlessly still.
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#6 Old 09-09-2008
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Ah, that is good to know. Thanks.
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#7 Old 09-10-2008
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Never thought about it except I accept it's like older cars... Choking the Carburetor.

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#8 Old 09-11-2008
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Never thought about it except I accept it's like older cars... Choking the Carburetor.
I remember so called "auto choke" when you press the gas/accelerator pedal all the way down once before starting the engine in cold winter months. The auto choke disengages when the engine warms up. I also recall the manual choke too, where one pulls out a round button/lever labeled CHOKE, start the engine and when it warms up, you would push the choke lever back in.

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#9 Old 09-11-2008
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Don't think i have heard that term used in ages now, I'm more used to hearing about it on aircraft engines than car's.

It's slightly put out by the fact that the SLK doesn't have one mind you.

I'm feeling all nostalgic right now.
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