Momentary Rough Idle?
Thread Starter
Senior Member
Joined: Oct 2004
Posts: 308
Likes: 0
From: Honolulu, Hawaii
2001 E55, 2002 ML55, 2002 SL500, 2003 CLK55
Momentary Rough Idle?
Started the car up from cold (85' day) and drove non-stop for about five miles then stopped at a stop-light. For about a second I had a rough idle then all was fine. The best way I can describe it is that it the car shook a bit and felt like it was going to die, idle might have blipped down a bit but it happened so fast that I didn't have time to look at the instruments.
I realize this is a shot in the dark but hoping someone has some insight.
Car has 62k on it and MAF has been cleaned recently. Plugs have all been changed about 10k ago and I diligently run fuel cleaner periodically.
Any ideas?
Thanks!
I realize this is a shot in the dark but hoping someone has some insight.
Car has 62k on it and MAF has been cleaned recently. Plugs have all been changed about 10k ago and I diligently run fuel cleaner periodically.
Any ideas?
Thanks!
Senior Member
Joined: Aug 2011
Posts: 271
Likes: 3
From: NY
1999 Mercedes Benz E55 AMG
Bad gas comes to mind. A lot of times it's as simple as that. I know you probably run 93,but sometimes even with that you can get a bad batch.
Have you ever changed the fuel filter?
Have you ever changed the fuel filter?
Senior Member
Joined: Oct 2006
Posts: 341
Likes: 0
From: Novato, California
2000 E55 AMG
Just a shot in the dark: Crank position sensor. Mine went out at 64K. It's a slow death. But, the CPS tends work fine at cold starts. Then it begins to fail as the engine warms up. Eventually, you may find yourself at the gas station not able to start your engine until the unit cools off. Good luck. 
Thread Starter
Senior Member
Joined: Oct 2004
Posts: 308
Likes: 0
From: Honolulu, Hawaii
2001 E55, 2002 ML55, 2002 SL500, 2003 CLK55
Thanks for the suggestions.
No, haven't changed the fuel filter but have one waiting to be installed!
I was thinking about the CPS too but thought the miles were too low. Just changed it on the ML.
I guess I'll go an order a CPS since it almost seems like a maintenance item!
No, haven't changed the fuel filter but have one waiting to be installed!
I was thinking about the CPS too but thought the miles were too low. Just changed it on the ML.
I guess I'll go an order a CPS since it almost seems like a maintenance item!
Senior Member
Joined: Aug 2011
Posts: 271
Likes: 3
From: NY
1999 Mercedes Benz E55 AMG
It's funny how you guys change CPSs for no reason...and this is not the first time I've had this conversation on here.
The CPS won't really give you warning signs,it will leave you stranded...the well known hot-cold. I just don't see why the car would shudder for a moment and the culprit would be the CPS. Maybe you ' felt ' the fan clutch kicking in faster at idle,sometimes it gives you that impression,as it can take quite a bit of engine power.
BTW,if you guys decide to replace your CPS,don't throw away the so called ' faulty ' one,just Pm me and I'll take it off your hands...I'll pay for shipping. That way I'll keep one in the car for when I'll really have a problem and be stranded.
The CPS won't really give you warning signs,it will leave you stranded...the well known hot-cold. I just don't see why the car would shudder for a moment and the culprit would be the CPS. Maybe you ' felt ' the fan clutch kicking in faster at idle,sometimes it gives you that impression,as it can take quite a bit of engine power.
BTW,if you guys decide to replace your CPS,don't throw away the so called ' faulty ' one,just Pm me and I'll take it off your hands...I'll pay for shipping. That way I'll keep one in the car for when I'll really have a problem and be stranded.
Last edited by Neanicu888; Oct 17, 2012 at 03:09 PM.
Senior Member
Joined: Aug 2011
Posts: 271
Likes: 3
From: NY
1999 Mercedes Benz E55 AMG
Also,if you're going to change your fuel filter,please listen to my advice....DO NOT and I repeat DO NOT,under any circumstance install an aftermarket fuel filter!!! Only install OEM from the dealer with the Mercedes part number on it. Or,if you buy it online,make sure it's OEM and that it has the Mercedes part number on it. This is very important because our cars have the fuel pressure regulator integrated in the fuel filter. A lot of people don't know this and they wonder how come they don't have fuel pressure...' Oooh...it's the pump ' . IT'S THE FUEL FILTER!!! The top hose that comes out of the fuel filter facing the front of the car is an engine vacuum hose. No gas should be present in that hose! If you have gas there,your filter it's toast. That is the fuel pressure regulator hose. Once the pump builds up pressure at the fuel rail,it will continue to maintain it until shut off. Then it's the fuel pressure regulator's job to keep it at the fuel rail for future start. If your fuel pressure regulator is bad it will allow the gas ' leak ' back down and you will have problems at start up and/or it can cause rough idle,no power etc.
Also,I recommend filling up the new filter with gas before installing it back in the car and starting. This will prevent the initial pressure flow on dry that can cause the rupture of the fuel pressure regulator's membrane,which would allow gas in the vacuum hose.
Also,I recommend filling up the new filter with gas before installing it back in the car and starting. This will prevent the initial pressure flow on dry that can cause the rupture of the fuel pressure regulator's membrane,which would allow gas in the vacuum hose.
Thread Starter
Senior Member
Joined: Oct 2004
Posts: 308
Likes: 0
From: Honolulu, Hawaii
2001 E55, 2002 ML55, 2002 SL500, 2003 CLK55
Also,if you're going to change your fuel filter,please listen to my advice....DO NOT and I repeat DO NOT,under any circumstance install an aftermarket fuel filter!!! Only install OEM from the dealer with the Mercedes part number on it. Or,if you buy it online,make sure it's OEM and that it has the Mercedes part number on it. This is very important because our cars have the fuel pressure regulator integrated in the fuel filter. A lot of people don't know this and they wonder how come they don't have fuel pressure...' Oooh...it's the pump ' . IT'S THE FUEL FILTER!!! The top hose that comes out of the fuel filter facing the front of the car is an engine vacuum hose. No gas should be present in that hose! If you have gas there,your filter it's toast. That is the fuel pressure regulator hose. Once the pump builds up pressure at the fuel rail,it will continue to maintain it until shut off. Then it's the fuel pressure regulator's job to keep it at the fuel rail for future start. If your fuel pressure regulator is bad it will allow the gas ' leak ' back down and you will have problems at start up and/or it can cause rough idle,no power etc.
Also,I recommend filling up the new filter with gas before installing it back in the car and starting. This will prevent the initial pressure flow on dry that can cause the rupture of the fuel pressure regulator's membrane,which would allow gas in the vacuum hose.
Also,I recommend filling up the new filter with gas before installing it back in the car and starting. This will prevent the initial pressure flow on dry that can cause the rupture of the fuel pressure regulator's membrane,which would allow gas in the vacuum hose.
I've read about this previously.
Thanks!
