SL/R129: 95 MB SL500 Rough RPM, Stalling, Check Engine Light
01-21-2019, 09:48 AM
#1
Newbie
Thread Starter
Join Date: Oct 2009
Posts: 1
Likes: 0
Received 0 Likes
on
0 Posts
MB 1995 SL500 Roadster Black
95 MB SL500 Rough RPM, Stalling, Check Engine Light
Hi all:
I'm looking for input from this group on a worsening intermittent rough engine problem I've had for over a year, now undrivable!
Initially replaced plugs with MB Dealer plugs. Seemed to help a little, but intermittent problem continued. Cleaned caps and rotors 2 months ago, need to purchase new. Also replaced fuel filter 3 months ago, no change.
The intermittent problem started with normal startup idle, then rough hesitation on applying throttle, like no power available, then somewhere around 40mph (and occasionally if I back off slightly on the throttle), the car will suddenly accelerate big time and smoothly. The most concerning part was the inability to accelerate at lower speeds and RPMs with people behind you getting annoyed. And it will occasionally idle roughly as well.
Fast forward to a few days ago. Drove to a destination 6 miles away, developed the rough underpowered acceleration 3 miles into it. Super rough idle at stop lights almost to the point of stalling. When car was turned off at destination, it seemed like it was going to stall before shutdown. Then I noticed a funny smell near the exhaust as I walked past it, like a burning electrical smell.
I came back to the car much sooner than normal and tried to start it with no success. Engine turned over fine, but wouldn't start. Got a ride home and came back with tools to check my plugs from a year ago...all looked new and super clean. Engine started (but over an hour had passed).
Tried to get the car home, but stalled when I tried to apply throttle at a traffic light 2 miles from home. What I noticed during that short drive was that when the RPM got super rough and dropped to 400 RPM, the MPG gauge pegged to the right at like "0" MPG, like the fuel mixture became SUPER Rich. When the RPM smoothed out momentarily, the MPG gauge shot to over 40 MPG (before applying throttle), indicating a Leaner mixture. **I really don't know which is occurring first, the rough RPM or the SUPER Rich mixture **.
Had to let the car sit for almost an hour before getting it to start, and then applied continuous throttle while braking at the light and finally limped it home. That's when I noticed the ENGINE light has come on for the first time ever (and I only have 95,000 miles on the car).
Researched my available onboard diagnostics and I'm disappointed to say I have the 38-pin module on the right side engine compartment near the hood hinge. I'm really hoping someone can offer a solution to read the codes off of this module other than taking it to the Dealer....
Also, any thoughts on further troubleshooting this problem and how to read the CEL codes would be appreciated.
Thanks!
Bill
I'm looking for input from this group on a worsening intermittent rough engine problem I've had for over a year, now undrivable!
Initially replaced plugs with MB Dealer plugs. Seemed to help a little, but intermittent problem continued. Cleaned caps and rotors 2 months ago, need to purchase new. Also replaced fuel filter 3 months ago, no change.
The intermittent problem started with normal startup idle, then rough hesitation on applying throttle, like no power available, then somewhere around 40mph (and occasionally if I back off slightly on the throttle), the car will suddenly accelerate big time and smoothly. The most concerning part was the inability to accelerate at lower speeds and RPMs with people behind you getting annoyed. And it will occasionally idle roughly as well.
Fast forward to a few days ago. Drove to a destination 6 miles away, developed the rough underpowered acceleration 3 miles into it. Super rough idle at stop lights almost to the point of stalling. When car was turned off at destination, it seemed like it was going to stall before shutdown. Then I noticed a funny smell near the exhaust as I walked past it, like a burning electrical smell.
I came back to the car much sooner than normal and tried to start it with no success. Engine turned over fine, but wouldn't start. Got a ride home and came back with tools to check my plugs from a year ago...all looked new and super clean. Engine started (but over an hour had passed).
Tried to get the car home, but stalled when I tried to apply throttle at a traffic light 2 miles from home. What I noticed during that short drive was that when the RPM got super rough and dropped to 400 RPM, the MPG gauge pegged to the right at like "0" MPG, like the fuel mixture became SUPER Rich. When the RPM smoothed out momentarily, the MPG gauge shot to over 40 MPG (before applying throttle), indicating a Leaner mixture. **I really don't know which is occurring first, the rough RPM or the SUPER Rich mixture **.
Had to let the car sit for almost an hour before getting it to start, and then applied continuous throttle while braking at the light and finally limped it home. That's when I noticed the ENGINE light has come on for the first time ever (and I only have 95,000 miles on the car).
Researched my available onboard diagnostics and I'm disappointed to say I have the 38-pin module on the right side engine compartment near the hood hinge. I'm really hoping someone can offer a solution to read the codes off of this module other than taking it to the Dealer....
Also, any thoughts on further troubleshooting this problem and how to read the CEL codes would be appreciated.
Thanks!
Bill
07-14-2021, 05:18 PM
#5
Newbie
Join Date: Jul 2021
Posts: 1
Likes: 0
Received 0 Likes
on
0 Posts
1998 Mercedes sl500
Hi all:
I'm looking for input from this group on a worsening intermittent rough engine problem I've had for over a year, now undrivable!
Initially replaced plugs with MB Dealer plugs. Seemed to help a little, but intermittent problem continued. Cleaned caps and rotors 2 months ago, need to purchase new. Also replaced fuel filter 3 months ago, no change.
The intermittent problem started with normal startup idle, then rough hesitation on applying throttle, like no power available, then somewhere around 40mph (and occasionally if I back off slightly on the throttle), the car will suddenly accelerate big time and smoothly. The most concerning part was the inability to accelerate at lower speeds and RPMs with people behind you getting annoyed. And it will occasionally idle roughly as well.
Fast forward to a few days ago. Drove to a destination 6 miles away, developed the rough underpowered acceleration 3 miles into it. Super rough idle at stop lights almost to the point of stalling. When car was turned off at destination, it seemed like it was going to stall before shutdown. Then I noticed a funny smell near the exhaust as I walked past it, like a burning electrical smell.
I came back to the car much sooner than normal and tried to start it with no success. Engine turned over fine, but wouldn't start. Got a ride home and came back with tools to check my plugs from a year ago...all looked new and super clean. Engine started (but over an hour had passed).
Tried to get the car home, but stalled when I tried to apply throttle at a traffic light 2 miles from home. What I noticed during that short drive was that when the RPM got super rough and dropped to 400 RPM, the MPG gauge pegged to the right at like "0" MPG, like the fuel mixture became SUPER Rich. When the RPM smoothed out momentarily, the MPG gauge shot to over 40 MPG (before applying throttle), indicating a Leaner mixture. **I really don't know which is occurring first, the rough RPM or the SUPER Rich mixture **.
Had to let the car sit for almost an hour before getting it to start, and then applied continuous throttle while braking at the light and finally limped it home. That's when I noticed the ENGINE light has come on for the first time ever (and I only have 95,000 miles on the car).
Researched my available onboard diagnostics and I'm disappointed to say I have the 38-pin module on the right side engine compartment near the hood hinge. I'm really hoping someone can offer a solution to read the codes off of this module other than taking it to the Dealer....
Also, any thoughts on further troubleshooting this problem and how to read the CEL codes would be appreciated.
Thanks!
Bill
I'm looking for input from this group on a worsening intermittent rough engine problem I've had for over a year, now undrivable!
Initially replaced plugs with MB Dealer plugs. Seemed to help a little, but intermittent problem continued. Cleaned caps and rotors 2 months ago, need to purchase new. Also replaced fuel filter 3 months ago, no change.
The intermittent problem started with normal startup idle, then rough hesitation on applying throttle, like no power available, then somewhere around 40mph (and occasionally if I back off slightly on the throttle), the car will suddenly accelerate big time and smoothly. The most concerning part was the inability to accelerate at lower speeds and RPMs with people behind you getting annoyed. And it will occasionally idle roughly as well.
Fast forward to a few days ago. Drove to a destination 6 miles away, developed the rough underpowered acceleration 3 miles into it. Super rough idle at stop lights almost to the point of stalling. When car was turned off at destination, it seemed like it was going to stall before shutdown. Then I noticed a funny smell near the exhaust as I walked past it, like a burning electrical smell.
I came back to the car much sooner than normal and tried to start it with no success. Engine turned over fine, but wouldn't start. Got a ride home and came back with tools to check my plugs from a year ago...all looked new and super clean. Engine started (but over an hour had passed).
Tried to get the car home, but stalled when I tried to apply throttle at a traffic light 2 miles from home. What I noticed during that short drive was that when the RPM got super rough and dropped to 400 RPM, the MPG gauge pegged to the right at like "0" MPG, like the fuel mixture became SUPER Rich. When the RPM smoothed out momentarily, the MPG gauge shot to over 40 MPG (before applying throttle), indicating a Leaner mixture. **I really don't know which is occurring first, the rough RPM or the SUPER Rich mixture **.
Had to let the car sit for almost an hour before getting it to start, and then applied continuous throttle while braking at the light and finally limped it home. That's when I noticed the ENGINE light has come on for the first time ever (and I only have 95,000 miles on the car).
Researched my available onboard diagnostics and I'm disappointed to say I have the 38-pin module on the right side engine compartment near the hood hinge. I'm really hoping someone can offer a solution to read the codes off of this module other than taking it to the Dealer....
Also, any thoughts on further troubleshooting this problem and how to read the CEL codes would be appreciated.
Thanks!
Bill
What was the cause of the problem I have a 98 sl500 that is doing the same exact thing?
thanks!
Nate
