I recently purchased a 2004 coupe. When I stop at stoplights or intersections the idle drops to 500rpm and the car is slightly rough at idle. As soon as it turns green and I accelerate there are no issues. I actually called the dealer who services the car before I bought it and he said that it is normal for the crossfire. It lowers the idle at stop and then resets after you accelerate. Anyone else have this with their car?

 

Do you have an AT or stick? I have a stick, and have noticed a couple of times mine idling a little rough & rich when backing in to the gargae, but it has come back up too. I haven't noticed it doing this at a light (but that doesn't mean that it hasn't).

 

Your dealer gave you what they all give their customers for free, a lie.
Mine idles at about 500 to 600 rpm but it is smooth. maybe you have a vacuum leak somewhere.

 

vacuum leak, dirty map sensor, even dirty air filters...start lookin'

 

x3

Jumping on the vacuum leak bandwagon.

 

Or, it could be a loose air intake tube.... After market CAI?

Airflow over the Map sensor is everything with these cars.

 

Try some fuel system cleaner. Also you are running premium?

 

I also have 2004 Coupe. Mine has done that sevral times. It has even stalled out a couple of time at the light. Once the check engine light came on the went off the next day. I took it ot the dealer for a check and they are replacing the Mass Air FLow Sensor and MAP Sensor. It was throwing P0175 and P0172 codes. Parts will be in on Tuesday. I will report back when parts are replaced

 

Rough idles are common on our cars. I have experienced it myself. But it all depends on how rough the idle is. If it is really rough (which I experienced while driving a demo back in 2005) then it is a vaccum line (which the dealer ended up fixing). But I have experienced an occasional stutter while sitting at a light. Never stalled or felt like it would.

Our cars are very unique... sometimes you notice engine noises. Sometimes you will hear a ticking from the engine. Lets face it.... they are noisy Mercedes. That is what makes our cars so special and unique. If you want a car that runs so smooth and quiet that you can't even tell if it is running then buy a Lexus.

 

Check for a vacum leak first and then get a spray can of brake parts cleaner and remove the MAF sensor and clean it. A rough dropping idle when you come to a stop or stall is the first sign of the CPS going bad.

 

My 04 had been fluctuating more than usual while stopped and would randomly turn CEL on/off. Pulled engine cover off, took filters out and wiped everything down with a microfiber. Intake tubes as well. There was a lot of dust build up at the tube connections and a couple leaves/bugs laying up by the filter. Shook the filters out and put everything back together. Acting much better and *** dyno says it's pulling slightly harder in mid range but that could just be in my head engine light went off right after doing it though. 10min job might be worth a shot

 

Thank you for all the suggestions. The car has an AT transmission and stock air cleaner. I changed the filters when I first bought the car a month ago. It idled quite rough and the filters were trashed. I put in K&N filters and it was 100% better. I took off the cover tonight and cleaned it. I checked most of the vacuum lines I could see visually and saw nothing loose or cracked. Not sure if there is any other way to check them? Tomorrow I will check the MAF sensor. Let me say that I could just be over the top on my expectations because the car does not stall, it just has a slight rough idle at stop lights. It does not seem to respond instantly if the car is in D from stop. However it is much better if I start out in 1st gear and shift through them. I appreciate everyone's time and suggestions.

 

Do a throttle reset. Turn the ignition on but don't start the car.
Depress the fuel throttle and hold to the floor for five seconds
Release the throttle and turn the ignition off but leave the keys in it.
Let it sit for at least two minutes.

Now, start the car. Reset complete.

It should eliminate that hesitation. At least back to factory performance.


Next, Get a Sprint Booster.

I'll bet this is happening during warm weather with you AC on? And I'll bet this is your first wireless throttle.

 

This throttle uses wires, it is cable less though.

 

your right, a oft made mistake when describing the disconnected throttle connection.

Somewhere in the little Black Module CPU is a canister of black smoke. It is how these mystical electronic things work. I know because whenever the black smoke escapes, they stop working.

My sub mental assertion is, therefore, that wires have nothing to do with it.

I have proven this theory on several occasions.

 

I was having a misfire. So i changed all my vacuum lines,intake gasket, plugs and wires. Ran worse than it did before.Then i found all my coil packs were cracked. Start up great when i replaced that. Drove down the road great but it idled horrible. Checked for leaks could find anything. So i started unhooking lines to see if anything made a difference. What i found if i unhook that line in the picture it idles prefect. Does anyone know what that is?

 

EGR valve.

 

Thanks. I was able to look up egr valve and found i had the vacuum lines hooked up wrong.Its running great again.