SL/R129: Idle surge, rough idle please help.
03-07-2018, 06:54 AM
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CLK W208
Idle surge, rough idle please help.
Hi guys, i have this strange idle surge when not moving, sometimes its perfect but most times this rough idle occurs. I have practically changed everything possible but still same issue. Once you drive its great above 2 rpm.
Changed: Ignition coils, ignition distributors and rotors, ignition wiring, eha valve, fuel injectors and seals, fuel filter, checked and replaced vacuum hoses, spark plugs. The fuel distributor is untoched from factory and is working properly and all lines are ok.
After all changes car is still acting the same.
Please help, as its been a year and I still have no solution.
My car is a 1991 500SL r129. I use only 95 octane fuel.
Changed: Ignition coils, ignition distributors and rotors, ignition wiring, eha valve, fuel injectors and seals, fuel filter, checked and replaced vacuum hoses, spark plugs. The fuel distributor is untoched from factory and is working properly and all lines are ok.
After all changes car is still acting the same.
Please help, as its been a year and I still have no solution.
My car is a 1991 500SL r129. I use only 95 octane fuel.
03-07-2018, 05:52 PM
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CLK W208
Thanks for your responce. Any idea on how to test or clean the throttle body. Mine is a 1991andcannot find anything about it. I have no ASR or any light on though.
Thanks
Thanks
03-08-2018, 03:34 PM
#4
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I'd use fuel injection diagnostics to perform some basic checks. Locate the round diagnostic connector on the inner fender by the ABS hydraulic unit. With the engine cold, not running, and key on measure the voltage between sockets #2 and #3: it should be roughly 70% of the battery voltage. Then with the engine running at operating temperature repeat the measurement: the voltage should be 40-60% of what you have at the battery and should fluctuate.
03-09-2018, 08:43 AM
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CLK W208
I'd use fuel injection diagnostics to perform some basic checks. Locate the round diagnostic connector on the inner fender by the ABS hydraulic unit. With the engine cold, not running, and key on measure the voltage between sockets #2 and #3: it should be roughly 70% of the battery voltage. Then with the engine running at operating temperature repeat the measurement: the voltage should be 40-60% of what you have at the battery and should fluctuate.
Thanks
03-11-2018, 06:53 AM
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CLK W208
Sorry you are right, I found the X11 9 pin next to abs.
i removed the intake manafold to reach and clean the throttle body and check the vacuum lines under. Once I reattach everything I will check the volts on pin two and three. I will report back shortly.
Thanks
i removed the intake manafold to reach and clean the throttle body and check the vacuum lines under. Once I reattach everything I will check the volts on pin two and three. I will report back shortly.
Thanks
03-11-2018, 09:56 AM
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CLK W208
Hi guys
Cleaning the throttle body and checking the vacuum lines after removing manifold slightly enhanced the surge, but still occurs.
I did check the X11 pin 2 & 3 and these are the readings I am getting.
8.36 volts when engine is off, switch is on, cold engine
6.6 to 7.4 volts when engine is on and operating temp.
My battery is reading 12.32 volts when engine off, and 13.65 volts when engine is running.
please advise
Cleaning the throttle body and checking the vacuum lines after removing manifold slightly enhanced the surge, but still occurs.
I did check the X11 pin 2 & 3 and these are the readings I am getting.
8.36 volts when engine is off, switch is on, cold engine
6.6 to 7.4 volts when engine is on and operating temp.
My battery is reading 12.32 volts when engine off, and 13.65 volts when engine is running.
please advise
Last edited by M*BENZ; 03-11-2018 at 11:12 AM.
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03-12-2018, 10:06 AM
#9
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The voltage you read at the diagnostic connector are all within specification.
I suppose your Overvoltage Protection Relay (OVP) may be faulty. They typically have the date of manufacturer printed on their side. If your car still has its original OVP, then consider replacing it.
The OVP is located among the electronic modules in the rear of the engine compartment. It has a red top with a clear plastic cover and a fuse installed.
I suppose your Overvoltage Protection Relay (OVP) may be faulty. They typically have the date of manufacturer printed on their side. If your car still has its original OVP, then consider replacing it.
The OVP is located among the electronic modules in the rear of the engine compartment. It has a red top with a clear plastic cover and a fuse installed.
04-04-2018, 06:02 AM
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CLK W208
The voltage you read at the diagnostic connector are all within specification.
I suppose your Overvoltage Protection Relay (OVP) may be faulty. They typically have the date of manufacturer printed on their side. If your car still has its original OVP, then consider replacing it.
The OVP is located among the electronic modules in the rear of the engine compartment. It has a red top with a clear plastic cover and a fuse installed.
I suppose your Overvoltage Protection Relay (OVP) may be faulty. They typically have the date of manufacturer printed on their side. If your car still has its original OVP, then consider replacing it.
The OVP is located among the electronic modules in the rear of the engine compartment. It has a red top with a clear plastic cover and a fuse installed.
i finally received the OVP relay, a genuin mercedes part, but the idle surge is still there. Cleaning the throttle body did improve it, but problem still comes and goes. I did reset the codes on car, drove it for two days, and read all codes again. There were no errors at all. Only error was on Socket #8 code 17, but that is because engine is off. I tried with engine on and there was no errors. This is for checking the crankshaft position sensor.
I ordered a new oem bosch oxygen sensor although I am not getting any errors from the 16-pin diagnostic.
Please advise on what else I can do.
04-10-2018, 09:42 AM
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CLK W208
Ok guys, installed new oem oxygen sensor but no difference. Now I checked pin 2 & 3 while key is on and engine off, i get 50% duty cycle.
With engine is on at operating temp my duty cycle is fluctuating around 51% at idle and 40% at 2500 rpm.
As I understand duty cycle with key is on and engine off should be 70%. Why am I getting 50%.
I am about to give up on this car, as I nearly changed everything and still have this rough intermittent idle problem. Please help.
With engine is on at operating temp my duty cycle is fluctuating around 51% at idle and 40% at 2500 rpm.
As I understand duty cycle with key is on and engine off should be 70%. Why am I getting 50%.
I am about to give up on this car, as I nearly changed everything and still have this rough intermittent idle problem. Please help.
05-01-2018, 07:46 PM
#14
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idle range
When running normally, my idle in Park is 698-700. c
Currently, upon starting the idle immediately surges to 1200 then drops off; then, without pausing, it goes back up to 1200 then down again, repeat until shut off. The car violently shudders tbe whole time.
Currently, upon starting the idle immediately surges to 1200 then drops off; then, without pausing, it goes back up to 1200 then down again, repeat until shut off. The car violently shudders tbe whole time.
05-04-2018, 05:11 AM
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CLK W208
Just to update everyone, I fixed the interminent idle surge issue after replacing all other parts as mentioned above. Although I had the car with 60K miles in like new condition it turned out to be the fuel distributor. I installed a used one from a local shop and my problem went away. I kept my fuel distributor and want to rebuild it now. Who manufactures the best quality rebuild kit.
Thanks
Thanks
02-28-2022, 02:42 AM
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1998 Mercedes SL500
Observation
Hey There,
I was having the same issue of surging at Idle, I originally thought it was the Idle Air Control causing it but after reading some of these posts I got a different idea. I had a backup camera monitor plugged into the cigarette lighter. When i removed it the idle was fine. After placing it back in the idle began to surge again. Not sure if this will help or not.
I was having the same issue of surging at Idle, I originally thought it was the Idle Air Control causing it but after reading some of these posts I got a different idea. I had a backup camera monitor plugged into the cigarette lighter. When i removed it the idle was fine. After placing it back in the idle began to surge again. Not sure if this will help or not.
02-28-2022, 09:50 AM
#18
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Is your car equipped with electronic fuel injection or mechanical fuel injection? If electronic, be aware that you probably have defective wiring throughout the car, including everything in the engine compartment. The insulation on all the wiring crumbles to dust and corrodes the wires, leading to shorts and crossed connections. The electronic throttles and mass flow sensors will need rewiring along with all the harnesses. Also the EHA computer may be damaged but can be repaired.
If your car has the mechanical fuel injection, I am less familiar with it--having owned two SEL 500/560
series with that system. They just required the replacement of all the idle air plastic tubing every other year. The heat in Houston would cause all of it to harden and begin leaking, and replacement en-mass was the most effective P.M. I am not aware of anything that is RPM sensitive in the system, However, I would suspect the emissions control stuff. The vapor canister ventilation/purge system is a prime suspect. The switch-over valve stuff , the canister, and all the hoses--all the way to it and to the tank need to be leak-free.
If your car has the mechanical fuel injection, I am less familiar with it--having owned two SEL 500/560
series with that system. They just required the replacement of all the idle air plastic tubing every other year. The heat in Houston would cause all of it to harden and begin leaking, and replacement en-mass was the most effective P.M. I am not aware of anything that is RPM sensitive in the system, However, I would suspect the emissions control stuff. The vapor canister ventilation/purge system is a prime suspect. The switch-over valve stuff , the canister, and all the hoses--all the way to it and to the tank need to be leak-free.
02-28-2022, 12:09 PM
#19
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MAS
Hi guys, i have this strange idle surge when not moving, sometimes its perfect but most times this rough idle occurs. I have practically changed everything possible but still same issue. Once you drive its great above 2 rpm.
Changed: Ignition coils, ignition distributors and rotors, ignition wiring, eha valve, fuel injectors and seals, fuel filter, checked and replaced vacuum hoses, spark plugs. The fuel distributor is untoched from factory and is working properly and all lines are ok.
After all changes car is still acting the same.
Please help, as its been a year and I still have no solution.
My car is a 1991 500SL r129. I use only 95 octane fuel.
Changed: Ignition coils, ignition distributors and rotors, ignition wiring, eha valve, fuel injectors and seals, fuel filter, checked and replaced vacuum hoses, spark plugs. The fuel distributor is untoched from factory and is working properly and all lines are ok.
After all changes car is still acting the same.
Please help, as its been a year and I still have no solution.
My car is a 1991 500SL r129. I use only 95 octane fuel.
