# drop in RPM's when coming to an idle



## panheadjdhess (Oct 18, 2008)

My `94 Jetta started acting up recently when I come to a stop. The RPM's drop down to about 400, then quickly rise back up to normal idle. Sometimes the engine will even die. Is this a possible vacum leak?? If so, any ideas where to start looking???


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## crashdriver (Feb 20, 2010)

*Re: drop in RPM's when coming to an idle (panheadjdhess)*

Got the same issue, usually when I feel it happening (it'll shake and feel like it's about to blow up) just blip the throttle and it usually solve the prob. Till you shut the car off and it resets the ECU. This is an occasional problem right, it dosen't happen every time?


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## ekashyap (Feb 21, 2008)

Change the mass air flow sensor. I had the EXACT same symptoms on my 99 mk3 jetta. Changed that part and everything was ok.


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## crashdriver (Feb 20, 2010)

*Re: (ekashyap)*

I'd go with this solution ^^ sounds like a more perminent fix


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## panheadjdhess (Oct 18, 2008)

*Re: (crashdriver)*

I thought I replaced the mass airflow sensor when I was trying last years to get it ready for inspection, but maybe I thought I did and bought a cam position sensor and forgot the air flow sensor. I'll give it a shot and let you know what happens after that. To reset the ECU, do I just need to unplug it, then plug it back in??? I bought a obd2 scanner with a 2x2 cable for obd1 but doubt it has the capability to reset the ECU.


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## panheadjdhess (Oct 18, 2008)

*Re: drop in RPM's when coming to an idle (panheadjdhess)*

I was just reminded, I did replace the Mass air flow sensor lat year. Car only has 2,000 mi , if that on it since running


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## golfer97 (Dec 11, 2008)

Got the same problem some people say it is the throttle body. Where exactly is the ecu and where would you unplug it from?


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## FL 2.0L (Aug 1, 2002)

Did you try cleaning out the idle stabilization valve?


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## xjoanx (Nov 12, 2007)

I second that you should clean the throttle body Unplug the big hose coming from air filter, have a friend step on the gas, spray Throttle body cleaner(dont overdo it), and place a rag under to catch dirtyness, reconnect air filter hose. 
Afterwards to reset the value unplug the battery a while and short the terminals (AWAY FROM BATTERY), the replug, turn ignition on without starting, dont touch the gas pedal, give it like 30 seconds, then start car.
Had exatly the same symptoms, this did it for me.
ECU=Electronic control unit(car computer), black box in raintray, the procedure described above will reset it, no need to unplug it.
Hope I was of help


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## panheadjdhess (Oct 18, 2008)

*Re: (xjoanx)*

ok, I'll giveit s hot this weekend and let you know the results. Thanks


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## Robert Roberts (Jan 30, 2009)

*Re: (panheadjdhess)*

Definitely sounds like a dirty throttle body or a vacuum leak.
As for the MAF, you don't just throw a new one at it for kicks. There are ways to test if it is gone south. One is to unplug it while the car is running. If the problem goes away, you know it is bad.
You can also clean it easily and inexpensively using Mass Airflow Sensor Cleaner. Bought it at Carquest. Cheap. Follow directions on can! http://****************.com/smile/emthup.gif http://****************.com/smile/emthup.gif


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## solidcustoms (Feb 2, 2010)

*Re: (Robert Roberts)*

if you live in a cold aera and you taking shorter trips your PRV PCV t valve what ever the kids are calling it these days might be loaded up with water check it man it affects idle im pretty sure


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## Robert Roberts (Jan 30, 2009)

*Re: (solidcustoms)*


_Quote, originally posted by *solidcustoms* »_if you live in a cold aera and you taking shorter trips your PRV PCV t valve what ever the kids are calling it these days might be loaded up with water check it man it affects idle im pretty sure

Never heard of that before. Nifty. http://****************.com/smile/emthup.gif


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## golfer97 (Dec 11, 2008)

*Re: (xjoanx)*

Sorry I tried this but what do you mean do you mean touch neg. and the positive wires together? if so mine dont reach so what should i do. Im confused


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## morrison (Jan 23, 2010)

i had the same problem with my 94 mk3. i changed the pcv pipe and that did it for me. on the older models those are known to rot out because they're just made of a hard plastic and they're not made to withstand the elements for 15 years. try that and let me know what happens


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## panheadjdhess (Oct 18, 2008)

*Re: (morrison)*

I take it you're referring to the pipe at the front lower section of the engine???


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## golfer97 (Dec 11, 2008)

Anyone?


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## chorales (Jan 2, 2004)

*Re: (golfer97)*

black thing sticking out of the top of the motor on the passenger side, one hose going off to the left and one going down to the crankcase.


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## golfer97 (Dec 11, 2008)

I know what that is but the resetting the tb how do you do that


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## georgekelp (Aug 15, 2005)

*Re: (golfer97)*

Does anyone know how to test the MAF on an OBDII car with a vag-com?
I am having the same problem as the original poster; it is intermittent and might not happen for weeks at a time, and then every once in a while at a stop the engine might bog and want to die.
Any input?


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## tdogg74 (Mar 1, 2002)

*FV-QR*

http://faculty.ccp.edu/faculty...g.htm


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