# 1999 Beetle GLS 1.8T Rough Idle



## Frankwhy (Oct 5, 2011)

Car was runing fine before, then un-used for over a month. Then when got started recently, it can start easily but the idle is rough runing up and down within several hundreds rpm and some time can idling like this for ever and some time just die. No CEL light and an OBD II scanner shows no code. 

Seems throttle response is good, can easily rev to 4 to 5000rpm, if gas pedal gets push to make rpm hold at 2500 rpm after warmed up, you can still see the engine run several hundred rpms up and down around 2500 rpm. 

Seems getting worse recently, any time the gas pedal get released the car will die. 

Any idea?


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## mullardel34 (Sep 26, 2011)

Rough idle without any fault-codes on the VW 1.8T engines can often be traced to vacuum leaks, so feel the vacuum lines and see if any segments feel aged/brittle and replace any marginal vacuum hose segments. Vacuum line hose is dirt-cheap, so replace anything even remotely marginal (it will inevitably fail at some point...)  

Another candidate for your rough idling is the MAF (mass air-flow) sensor. When the MAF is marginal (beginning the gradual slide towards a complete failure), it won't necessarily throw a fault-code. MAF's run anywhere from about $100 up to around $220; the price depends upon your car's OEM engine-code (examples: AWV, APH & AWP engine codes). 

Good luck smoothing out the engine idle!


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## Frankwhy (Oct 5, 2011)

mullardel34 said:


> Rough idle without any fault-codes on the VW 1.8T engines can often be traced to vacuum leaks, so feel the vacuum lines and see if any segments feel aged/brittle and replace any marginal vacuum hose segments. Vacuum line hose is dirt-cheap, so replace anything even remotely marginal (it will inevitably fail at some point...)
> 
> Another candidate for your rough idling is the MAF (mass air-flow) sensor. When the MAF is marginal (beginning the gradual slide towards a complete failure), it won't necessarily throw a fault-code. MAF's run anywhere from about $100 up to around $220; the price depends upon your car's OEM engine-code (examples: AWV, APH & AWP engine codes).
> 
> Good luck smoothing out the engine idle!


 ========================== 

Thanks for the input. 

All the vaccum lines are replaced after rough idle found. Nothing changed. 

I have a good MAP at hand and will replace it to see what happens. I was thinking if the MAP bad there would be a code.


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## mullardel34 (Sep 26, 2011)

OK, good to hear that you've already eliminated vacuum lines; that's usually the best place to start your diagnostic efforts for rough-idle behavior.  

As I noted, sometimes when the MAF is just beginning to fail, it can prompt some ugly engine behavior without throwing a fault-code/DTC. The widely-varying idle RPM certainly sounds like something a failing MAF would cause to occur. Good luck!


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## haroldpo (Aug 3, 2011)

Did your battery go dead while it was un-used?


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## Frankwhy (Oct 5, 2011)

mullardel34 said:


> OK, good to hear that you've already eliminated vacuum lines; that's usually the best place to start your diagnostic efforts for rough-idle behavior.
> 
> As I noted, sometimes when the MAF is just beginning to fail, it can prompt some ugly engine behavior without throwing a fault-code/DTC. The widely-varying idle RPM certainly sounds like something a failing MAF would cause to occur. Good luck!


 ================================= 

You are totally right. I was thinking of MAP sensor. 

This afternoon I tried the MAF sensor, just unpluged it and the engine return to normal idle, smooth and stable, so the problem IS the MAF sensor. 

Will get a new one and test it. I am thinking of get one from Ebay, about $50 a piece, dealer sells for a lot more. Do you think the one from Ebay works ok?


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## Frankwhy (Oct 5, 2011)

haroldpo said:


> Did your battery go dead while it was un-used?


 ========================== 

Battery still good.


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## mullardel34 (Sep 26, 2011)

Glad to hear that you've identified the MAF sensor as your problem component. Ordering parts from Ebay is something of a crap-shoot; if you've had a good experience with a particular vendor, you're probably in good shape. Otherwise, I'm afraid it's a case of caveat emptor (buyer beware...). 

Good luck!


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## Frankwhy (Oct 5, 2011)

mullardel34 said:


> Rough idle without any fault-codes on the VW 1.8T engines can often be traced to vacuum leaks, so feel the vacuum lines and see if any segments feel aged/brittle and replace any marginal vacuum hose segments. Vacuum line hose is dirt-cheap, so replace anything even remotely marginal (it will inevitably fail at some point...)
> 
> Another candidate for your rough idling is the MAF (mass air-flow) sensor. When the MAF is marginal (beginning the gradual slide towards a complete failure), it won't necessarily throw a fault-code. MAF's run anywhere from about $100 up to around $220; the price depends upon your car's OEM engine-code (examples: AWV, APH & AWP engine codes).
> 
> Good luck smoothing out the engine idle!


 ============================ 

What do you mean by engine code AWV, APH and AWP? I only know my engine is 1.8T. Where this code located? 

I saw people selling this sensor on ebay only saying for 1.8T engine.


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## haroldpo (Aug 3, 2011)

Frankwhy said:


> ==========================
> 
> Battery still good.


 Did it go dead while sitting and had to be recharged?


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