Idle speed increasing

cheefpilot

Well-known member
Joined
Aug 31, 2009
Location
Texas
TDI
2013 JSW
Sometimes when I come to a stop, my idle speed will start to increase after a few moments. Usually it is a slow but steady increase of about 150-200 rpm while I'm waiting at a traffic light. VCDS scan shows no obvious problems and the engine runs great other than this oddity that I can't figure out. Have any of you had this problem on your cars?
 

Seatman

Top Post Dawg
Joined
Apr 23, 2010
Location
Scotland
TDI
2014 Skoda rapid elegance 1.6 cr tdi
I wonder if it could be the cts (coolant temp sensor) I know it can cause the idle to act up in our older VE type engines. maybe it might show up as a funny temp reading in VCDS.
 

cheefpilot

Well-known member
Joined
Aug 31, 2009
Location
Texas
TDI
2013 JSW
Coolant temp readings are steady, must be something else. I've also noticed that engine temp doesn't seem to be a factor, it does this when it is cold and at normal temps.
 

nord

Veteran Member
Joined
Mar 5, 2010
Location
Southern Tier NY
TDI
All turned back to VW. Now a 2017 Hundai Tuscon. Not a single squalk in 10k miles.
Electrical load would be my first guess. The ECU will increase revs to compensate for battery drain at idle speeds. This might also be a good time to have your battery tested as well as your alternator. Make sure that you're seeing roughly 13.5v. If not, then it's time to find out why.
 

cheefpilot

Well-known member
Joined
Aug 31, 2009
Location
Texas
TDI
2013 JSW
Alternator voltage is good but my battery has been weak lately. I'll replace it and see if that helps.
 

cheefpilot

Well-known member
Joined
Aug 31, 2009
Location
Texas
TDI
2013 JSW
Well it wasn't the battery. Any other possible reasons why the ECU would command an idle speed increase?
 

bsbaron1

Well-known member
Joined
Nov 20, 2010
Location
columbus,nc
TDI
06 jetta
Idle increase

I have also had this symptom for about a year.I sure would like to know what is causing this.
 

compu_85

Gadget Guy
Joined
Sep 29, 2003
Location
La Conner, WA
TDI
... None :S
Just because the gauge is steady doesn't mean the coolant temp sensor is OK, the computer doesn't use the same output as the gauge.

-J
 

Seatman

Top Post Dawg
Joined
Apr 23, 2010
Location
Scotland
TDI
2014 Skoda rapid elegance 1.6 cr tdi
Just check the temp in vcds/vagcom, it takes the reading from the ecu side of the sensor I think and should show up as running cool or cold. That's how I discovered my t stat was bad, it showed up as to cold when checking the timing.
 

cheefpilot

Well-known member
Joined
Aug 31, 2009
Location
Texas
TDI
2013 JSW
Been driving around with the VCDS hooked up for a few days and just can't find anything out of the ordinary. All of the numbers look normal. I've noticed that at night the lights will get slightly dimmer at idle and almost flicker a bit in sync with the engine so I suspect the alternator may be on the way out. That could be the problem, maybe the engine is increasing speed to get more alternator current but it seems like I would see some difference in voltage reading in VCDS instead of a steady 14v. Oh well, I guess i will just ignore it for now since it runs great otherwise.
 

shaark92

Veteran Member
Joined
Dec 29, 2005
Location
Erath County, Texas
TDI
06 Jetta, manual. '12 Jetta, DSG
I had this. The motor which operates the cold air intake diverter (?) had failed ... essentially ran in a "choked" condition. I took it to the Autobahn for them to look as they did the regular rotate/balance of tires, but it was a simple fix.
 

nord

Veteran Member
Joined
Mar 5, 2010
Location
Southern Tier NY
TDI
All turned back to VW. Now a 2017 Hundai Tuscon. Not a single squalk in 10k miles.
Either I'm not understanding or someone was shoveling manure in your direction. The only "choke" in the entire intake system is the ASV (Anti Shudder Valve). This little fellow will typically strip its gears and fail to close. I suppose in some cases the gears will bind and cause it not to open but this would be rare. It has nothing to do with warm or cold air... Just charge air.

In any case the ASV would not in my opinion cause the idle to increase as idle is controlled by fueling and fueling by the ECM. I other words the ECM would essentially be stepping slightly on the accelerator. Reasons for this are varied. Ambient temperature, electrical load, and I suppose other reason unknown to me.

My guess remains electrical load. My reasoning being that the auxiliary heating element activates under cold conditions and demands a lot of current. The ECM senses this load and reacts by increasing fuel delivery until such time as it's not needed.

The one thing I do suspect is that someone has installed an underrated alternator at some point. Even if properly installed and equipped with a clutch it would not produce enough current to satisfy the demands of a cold vehicle at normal idle. The ECU would not be able to determine anything other than the fact that load exceeded capacity and thus would up the idle speed slightly to compensate.

My opinion.
 

GoFaster

Moderator at Large
Joined
Jun 16, 1999
Location
Brampton, Ontario, Canada
TDI
2006 Jetta TDI
Been driving around with the VCDS hooked up for a few days and just can't find anything out of the ordinary. All of the numbers look normal. I've noticed that at night the lights will get slightly dimmer at idle and almost flicker a bit in sync with the engine so I suspect the alternator may be on the way out. That could be the problem, maybe the engine is increasing speed to get more alternator current but it seems like I would see some difference in voltage reading in VCDS instead of a steady 14v. Oh well, I guess i will just ignore it for now since it runs great otherwise.
If the charging voltage is low, the system will bump up the idle speed in an attempt to charge more. If your alternator is going bad, this will happen, and it could be intermittent if whatever the issue is with the alternator, is also intermittent.

I've had this happen twice, and both times, it was because the alternator drive pulley was going bad, and not consistently driving the alternator at full speed.
 

cheefpilot

Well-known member
Joined
Aug 31, 2009
Location
Texas
TDI
2013 JSW
Please tell me more about the alternator pulley and how I would check to see if that may be my problem.
 

GoFaster

Moderator at Large
Joined
Jun 16, 1999
Location
Brampton, Ontario, Canada
TDI
2006 Jetta TDI
Rattly-squeak noise coming from the area of the alternator pulley.

Eventually the rattly-squeak turns into a tortured-metal death-rattly-squeak/squeal, and in my experience, very shortly after this, there is a THUMP followed immediately by the alternator-failure warning lamp (and it all goes quiet again), after which the offending alternator pulley will be found on the top of your belly pan along with the belt!

You can drive the car with the serpentine belt off, as long as the battery will last. There's nothing immediately mission-critical driven by that belt - only the A/C and the alternator. I needed half an hour to get to my buddy's shop ... made it there with plenty of battery charge to spare. I turned off everything possible that was operated by electricity.
 

Dalon

Veteran Member
Joined
Apr 6, 2015
Location
Ohio
TDI
2006 MKV Jetta TDI 1.9L - 210k 2013 Passat TDI - 27k
Did you ever find the culprit? I have the same issue. Car will start and idle at normal RPM, the randomly go to 900 or 1000. Going to get the multimeter and check it tomorrow with the car off and on to see what voltage measures across the battery to try and rule out charging/battery as the issue
EDIT: I realize this thread is quite old but I’ve seen revivals in the past lol
 

BamaB4S

Veteran Member
Joined
Oct 28, 2011
Location
AL
TDI
1996 Passat
As he stated above, the culprit was failure of the alternator pulley/bearing
 

Dalon

Veteran Member
Joined
Apr 6, 2015
Location
Ohio
TDI
2006 MKV Jetta TDI 1.9L - 210k 2013 Passat TDI - 27k
As he stated above, the culprit was failure of the alternator pulley/bearing
Ah. I’ll have to do some troubleshooting to confirm an issue with the charging system then. Plan is to shoot voltage across the battery at standard idle and also with car off and then a few hours later to see if the battery is maintaining voltage
 

Dalon

Veteran Member
Joined
Apr 6, 2015
Location
Ohio
TDI
2006 MKV Jetta TDI 1.9L - 210k 2013 Passat TDI - 27k
Ah. I’ll have to do some troubleshooting to confirm an issue with the charging system then. Plan is to shoot voltage across the battery at standard idle and also with car off and then a few hours later to see if the battery is maintaining voltage
Ah found my issue. Battery voltage with car off is ~12.7, with car on it’s also ~12.7 :( new alternator on the way
 
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