99 C280 Rough IDLE!!!!! PLEASE HELP!!! - PeachParts Mercedes-Benz Forum

jenjenstar · #1 08-14-2008, 02:47 AM

PLEASE HELP!!!!!!!!!!
When my C280 warms up and is stopped it idles really rough! Just starts shaking while in place. Also I've now noticed that recently when the AC is on high it will shake the entire dash.

I've just fixed the power seats now this! I'm trying to sell it on my own but its a huge turn off when someone goes for a ride and it starts shaking really bad

. Please help. There is no way I can afford to pay a mechanic for a diagnostic test and its hard to trust what they're saying all the time since I'm a girl its easy to get the wool pulled over your eyes.

jenjenstar

the tenor man · #2 08-14-2008, 07:18 AM

It's pretty tough to diagnose idling problems. Is this when you just start it, or does it do it all of the time?

The first thing I would check is to see that all of the spark plug wires are connected correctly to the spark plugs. Maybe one of them has fallen off. If not, you may need to pull the sparkplugs and take a look at those.

Sometimes a vacuum leak will cause rough idling, check to see if a vacuum hose has fallen off.

Sometimes contaminated fuel will cause a problem like this...Did this begin to occur after refueling? Let us know how long this has be happening and how many miles are on the car.

Hope this helps.

The Tenor Man

jenjenstar · #3 08-15-2008, 06:53 PM

Quote:

Originally Posted by the tenor man

It's pretty tough to diagnose idling problems. Is this when you just start it, or does it do it all of the time?

The first thing I would check is to see that all of the spark plug wires are connected correctly to the spark plugs. Maybe one of them has fallen off. If not, you may need to pull the sparkplugs and take a look at those.

Sometimes a vacuum leak will cause rough idling, check to see if a vacuum hose has fallen off.

Sometimes contaminated fuel will cause a problem like this...Did this begin to occur after refueling? Let us know how long this has be happening and how many miles are on the car.

Hope this helps.

The Tenor Man

The car has 174k miles. It actually starts when the car has been running for about 10 minutes so pretty immediate. I did have the spark plugs changed about 2-3 years ago but never the wires. If the wires are NOT connected correctly is this something that will be noticeable?

Yes it does happen pretty much all the time (before and after refueling). It has been going on for the last couple of years and will come and go in streaks but now its just constant. Should I start with the spark plug wires? what should I look for?

jenjenstar · #4 08-15-2008, 06:55 PM

Quote:

Originally Posted by willp621

Just went through this on my 95 C-280. Ultimately, my problem was the connectors that connect the 3 coils to the spark plugs. Check those for signs of arcing (burn marks)....you can also check the plugs and wires. If even one of these connectors is bad it will throw the whole engine out of whack. Start with these components as they are inexpensive and can be changed easily.

I know this is going to sounds dumb but are the connectors the same as the spark plug wires? if not where are the connectors and what do they look like?

Devil Dog · #5 08-15-2008, 09:18 PM

Jen the vacum lines are plastic brittle and break really easy like spegetti I had rough idel and it was the lines but I got a light on the dash.I would not mess withthe wires as I have broken my taking them off.Installing the plugs is easy but the wires are something else you need instructions.Maybe someone will post them for you as I dont have any pics...You could have bad plugs installed wrong or they broke th wires by not knowing if mercedes did not change them....

the tenor man · #6 08-16-2008, 08:34 PM

My thoughts are that if it's been going on for a long time, (months-years?) but was first intermittent, there may be a corroded connection...easy to say, but tough to find...

If it runs fine at start-up and after ten minutes or so begins to miss...it seems as if the heat generated by the engine or a component that opens-up (stops working correctly) is the culprit...and they are difficult to find.

Here are some of the thoughts that come to mind...bad spark-plugs (unlikely but they are the least expensive item on the list), bad spark plug wires (or connectors), throttle position sensor, incorrect fuel pump pressure, clogged fuel filter, faulty oxygen sensor (if you're seeing your "check engine light"), faulty engine control module...and because of its high mileage, you may want to add worn engine parts...unlikely, but without complete service records, there is always a chance.

If you are good with tools and have a working knowledge of repairing the complicated systems on today's modern vehicles, I would suggest a service manual (Haynes and others) available for your model. Some of these have troubleshooting sections which may help. You'll also learn how to identify the various components of the engine.

If this seems beyond the scope of your knowledge, you'll have to have professional diagnose the problem and replace the defective part(s). I don't want to seem unfriendly...in fact, I'd like to help, but there only so many options available without actually seeing the car.

If you're trying to sell it, and the car looks good, I'm sure it will sell. But if will have to run flawlessly to get the top price. Because it's a "later model", there will be less "crazies" (like me) that would be willing to adopt a needy car and bring it back to life...

Hope this helps you make your decision...

The Tenor Man

cudaspaz · #7 08-16-2008, 10:23 PM

Tap on the mass airflow sensor while the car is running at idle, tap on it pretty hard like you are knocking on someones door.

Sometimes the idle will change drastically, if it does fluctuate noticeably, that is a real good indication th emass airflow sensor needs replaced.

Is the check engine light on?
You can get your check engine light diagnosed free from most large chain auto parts stores like advance with no obligation of repairs.

Your motor mounts also may be plain worn out causing the engine to feel rougher than it should.

When you start the car up do you feel a semi violent rumble in the drivers seat?

This is usually an idication of worn or broken motor mounts.

Any more issues, send me a P/M and I'll try to walk you through it.

Arthur Dalton · #8 08-18-2008, 11:45 AM

[QUOTE=willp621;1941771]The coil to plug connectors are a rubber tube-like item about 4 inches in length and 1 inch in diameter. One end snaps onto the coil and the other directly onto the top of the spark plug. There are 3- one for each of the 3 coils on this engine. You can buy these here online or at your local NAPA Auto Parts store (aftermarket).
The actual Mercedes-Benz part # is 000-1593642>>>

The car in question is a 1999 with a 112/V-6 and does not use the Waste Spark system or connectors.