Uneven Tick over

[John77]

Hi When I start the car it has an uneven tick over until I drive off. Also when stopped at lights the engine runs slightly uneven. There are no fault codes. I have just had a new MAF fitted, but it also did this before it was fitted. Any ideas.

2005 E200.

 

[ajlsl600]

Inlet pipe ,fitting leak ?

 

[John77]

Inlet pipe ,fitting leak ?

Hi thank you. You need to be more specific if possible. Do you mean this?
https://www.bing.com/videos/search?...FD8CAC4E904F61997898FD8&view=detail&FORM=VIRE

 

[ajlsl600]

Any air leak on induction after the maf can /will effect engine idle as the info its giving ecm will be compromised by the leak.

 

[John77]

Any air leak on induction after the maf can /will effect engine idle as the info its giving ecm will be compromised by the leak.

Hi thank you. I did replace the 2 breather pipes that is recommended but the very bottom one is quite inaccessible.

 

[ajlsl600]

Acceptability post sales aint high on benz priority, I have spent hrs cutting ,lengthening ,altering tools to get at various bits on my car,some of which dealers say,engine out! With the aggro and labour involved. Drop motor to get at starter,nuts !!

 

[Conor]

Hi When I start the car it has an uneven tick over until I drive off. Also when stopped at lights the engine runs slightly uneven. There are no fault codes. I have just had a new MAF fitted, but it also did this before it was fitted. Any ideas.

2005 E200.

Hey John,

Sounds like you have a vacuum leak. I studied this recently on my own car. Supposedly crankcase vacuum is at it's highest during idle. This means if there is a leak anywhere in the system after the MAF sensor, you will get the rough idle like you describe, at idle.

While there are a number of ways for checking for a vacuum, an old school way is to use a flammable spray. What you do is spray the fluid (I use cold start spray) around the various parts you think are leaking. When you hit the leak the fluid will get pulled into ignition and you will notice a blip of smooth running until that fluid burnt then it goes back to rough.

Be careful as the fluid could ignite when it hits something hot, so best do it from a cold start of the engine. Also if you find yourself spraying loads.. pause for a moment or two to let the fumes evaporate, in order to prevent a huge flame if something does ignite. It's safe, don't worry

How long has this been going on for? Did you ever get an engine light showing?

Do you have a scanner?

 

[John77]

Hey John,

Sounds like you have a vacuum leak. I studied this recently on my own car. Supposedly crankcase vacuum is at it's highest during idle. This means if there is a leak anywhere in the system after the MAF sensor, you will get the rough idle like you describe, at idle.

While there are a number of ways for checking for a vacuum, an old school way is to use a flammable spray. What you do is spray the fluid (I use cold start spray) around the various parts you think are leaking. When you hit the leak the fluid will get pulled into ignition and you will notice a blip of smooth running until that fluid burnt then it goes back to rough.

Be careful as the fluid could ignite when it hits something hot, so best do it from a cold start of the engine. Also if you find yourself spraying loads.. pause for a moment or two to let the fumes evaporate, in order to prevent a huge flame if something does ignite. It's safe, don't worry

How long has this been going on for? Did you ever get an engine light showing?

Do you have a scanner?

Hi thank you for the information. This has actually been going on for about a year with when at lights sometimes a little shudder and the lights comes on. Yes scanner said the MAF so eventually changed that 3 weeks ago and it does run differently since, smoother acceleration, but still the very uneven start up and just uneven at stops like junctions and lights.
No new engine lights or fault codes since new Maf.

 

[Conor]

Hi thank you for the information. This has actually been going on for about a year with when at lights sometimes a little shudder and the lights comes on. Yes scanner said the MAF so eventually changed that 3 weeks ago and it does run differently since, smoother acceleration, but still the very uneven start up and just uneven at stops like junctions and lights.
No new engine lights or fault codes since new Maf.

Ok, who changed the MAF? Was there an engine light prior to changing the MAF? Also how many miles have you done since changing MAF?

Reason I ask is because it is likely the error codes were cleared when MAF changed. If there is actually a vacuum leak then it will upset the fuel trims triggering an engine light/code, but this takes approximately a few hundred miles to re-appear.

 

[Brian23]

Ok, who changed the MAF? Was there an engine light prior to changing the MAF? Also how many miles have you done since changing MAF?

Reason I ask is because it is likely the error codes were cleared when MAF changed. If there is actually a vacuum leak then it will upset the fuel trims triggering an engine light/code, but this takes approximately a few hundred miles to re-appear.

Hi I changed the MAF and breather pipes all MB. Cleared all codes. Yes engine lights before MAF change. Faults said MAF. NO faults, since fitting. A couple of hundred miles since fitting.

 

[Conor]

Hi I changed the MAF and breather pipes all MB. Cleared all codes. Yes engine lights before MAF change. Faults said MAF. NO faults, since fitting. A couple of hundred miles since fitting.

Ok cool, not doubting the MAF problem, just wondering what the situation was.

The rough idle sounds like a vacuum leak, at least it was for me.

 

[Brian23]

Ok cool, not doubting the MAF problem, just wondering what the situation was.

The rough idle sounds like a vacuum leak, at least it was for me.

No thank you for taking the time to help.

 

[John77]

Hey John,

Sounds like you have a vacuum leak. I studied this recently on my own car. Supposedly crankcase vacuum is at it's highest during idle. This means if there is a leak anywhere in the system after the MAF sensor, you will get the rough idle like you describe, at idle.

While there are a number of ways for checking for a vacuum, an old school way is to use a flammable spray. What you do is spray the fluid (I use cold start spray) around the various parts you think are leaking. When you hit the leak the fluid will get pulled into ignition and you will notice a blip of smooth running until that fluid burnt then it goes back to rough.

Be careful as the fluid could ignite when it hits something hot, so best do it from a cold start of the engine. Also if you find yourself spraying loads.. pause for a moment or two to let the fumes evaporate, in order to prevent a huge flame if something does ignite. It's safe, don't worry

How long has this been going on for? Did you ever get an engine light showing?

Do you have a scanner?

Hi sorry for the late reply. Interesting idea with the fluid. This has been going on for a bout a year. Light comes on for an unspecified time, then next time in the car or on a run it will go out. There were fault codes before fitting the new, but non after, but I will check again. It is a pain also for the MoT if it comes on as it is a fail. Car runs fine when it is not idling.

 

[Conor]

Hi sorry for the late reply. Interesting idea with the fluid. This has been going on for a bout a year. Light comes on for an unspecified time, then next time in the car or on a run it will go out. There were fault codes before fitting the new, but non after, but I will check again. It is a pain also for the MoT if it comes on as it is a fail. Car runs fine when it is not idling.

Ahhh.. that sounds exactly like what I had. When I changed the PCV Valve the engine light hasn't returned.

For me it was fuel trims that were all over the place and a mixture of lean/rich errors.

Typically the car samples the values over a prolonged period of time and if they are problematic a light is show. When you reset the light you have another few hundred miles or so before it will come on. I suggest clearing the errors/light prior to the test.... and solving the underlying problem too

 

[John77]

Thank you I will do that, but at the moment I am sorting out the battery light visit workshop. Another thread.