# Rough/Shaky/Jittery Idle‏



## roy.vanegas (Jul 24, 2008)

car idles roughly
Hi,
A few months ago, my 1997 VW Jetta GL 2.0L began to idle roughly. 
(Incidentally, I've also been getting very poor mileage: about 18 
miles per gallon.) Since the Electronic Control Unit (ECU) hadn't 
triggered any Diagnostic Trouble Codes (DTCs), I tried to locate the 
problem on my own. I replaced
. the temperature sensor
. spark plugs
. distributor cap and rotor
. ignition wires
to no avail. A few weeks later, the ECU finally triggered a handful
of DTCs:
P0172: System Too Rich (Bank 1)
P0440: Evaporative Emission System
P0442: Evaporative Emission System Leak Detected (small leak)
I have a good idea about where to look to solve the last two DTCs, but
I'm not sure about the first one.
Anyone else have this problem?
Thanks in advance,
Roy


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## nab5126 (Dec 4, 2007)

*Re: Rough/Shaky/Jittery Idle‏ (roy.vanegas)*

sounds like a vaccum leak, check all your vac hoses off the manifold if they look old go get some new ones from a local auto parts store


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## roy.vanegas (Jul 24, 2008)

*Re: Rough/Shaky/Jittery Idle (nab5126)*

Will do. I'll post again after I replace the hoses, clear the DTCs, and run the car through a drive cycle with my scan tool.


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## roy.vanegas (Jul 24, 2008)

*Re: Rough/Shaky/Jittery Idle (roy.vanegas)*

i checked the hoses leading to the evap system and intake manifold, examined the evap canister and mass air flow sensor, and tested the intake air temperature sensor.
first, the hoses.
the braided hose from the intake manifold to the fuel pressure regular was in bad shape, but manifested only a tiny leak. i replaced it, nonetheless.
the braided hose from the intake manifold to the air cleaner was also in really bad shape, but only suffered from an almost invisible leak. i replaced that, too.
the rubber hose from the throttle valve to the evap canister was leaking. of course, this one
had to be replaced.
since i had to remove the air cleaner assembly to reach the evap canister, i thoroughly cleaned the inside of the assembly and the mass air flow sensor, which is housed in a rubber hose connected to the air cleaner assembly.
i used cotton swabs and alcohol to clean the throttle plate inside the throttle valve, but only on the surface.
i tested the intake air temperature sensor, which was fine.
after all that, i connected my scan tool, cleared the diagnostic trouble codes, which eliminated the check engine light, and began a full drive cycle. it didn't stall hard the way it used to, but still idled a little rough. nonetheless, there's a big improvement in how the car idles.
the next day, i finished the drive cycle. none of the dtcs have returned, but as i mentioned earlier, i'm still getting a lightly rough idle. some say the oxygen sensor (o2) and some say the ignition coil. thoughts?
thanks,
roy


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## 98RedBug (Oct 10, 2008)

*Re: Rough/Shaky/Jittery Idle (roy.vanegas)*

Did you check air filter? Fuel filter?


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## roy.vanegas (Jul 24, 2008)

air filter: new
fuel filter: new


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## FL 2.0L (Aug 1, 2002)

I'd try the coil if you have the money to throw at it. If it is original, the housing has to be cracked.


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## M0M0G60 (Apr 30, 2005)

*Re: Rough/Shaky/Jittery Idle‏ (roy.vanegas)*

I would check out the Purge valve near air box for eather stuck open or inoperative...


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## roy.vanegas (Jul 24, 2008)

i checked the ignition coil with a multimeter today -- it gave me too much resistance (1.3k ohms across the covered terminals, when i should've gotten between 0.5k and 0.7k ohms). i also found a slight crack on the coil's housing.


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## roy.vanegas (Jul 24, 2008)

i replaced the ignition coil yesterday. the rough idling has been somewhat mollified, but essentially is still present. 
i forgot to mention, however, that the rough idling ONLY occurs once the car is hot.
also, the poor mileage i've been receiving has gotten better: now i'm getting about 21 miles per gallon.


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## roy.vanegas (Jul 24, 2008)

i got back the
P0442: Evaporative Emission System Leak Detected (small leak)
error code today. my gas cap isn't original. in fact, it's some crappy $5 cap that the previous owner had been using. would replacing that with an oem gas cap fix this p0442 issue?


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## Jay-Bee (Sep 22, 2007)

*Re: (roy.vanegas)*


_Quote, originally posted by *roy.vanegas* »_i got back the
P0442: Evaporative Emission System Leak Detected (small leak)
error code today. my gas cap isn't original. in fact, it's some crappy $5 cap that the previous owner had been using. would replacing that with an oem gas cap fix this p0442 issue?


More than likely yes.
And a vacuum leak shouldn't be related to a "System too rich" code. 
Vacuum leaks (more air than metered) would create a lean condition.


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## tdogg74 (Mar 1, 2002)

*FV-QR*

>21mpg and sh*tty idle when hot....the O2 sensor would have been the first thing I replaced.


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## roy.vanegas (Jul 24, 2008)

I replaced the O2 (oxygen sensor) yesterday. The car still idles rough.
So, to recap, I 
. replaced the spark plugs
. replaced the spark plug wires
. replaced the air filter
. replaced the fuel filter
. replaced the temperature sensor
. distributor cap and rotor
. replaced the ignition coil
. replaced a bunch of hoses to the intake air manifold
. replaced the hoses leading from the evap canister to the throttle
I'm going to check the purge valve next. Any ideas after that?


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## GottaSeeThis (Oct 29, 2008)

*Re: (roy.vanegas)*

Check the PCV hoses and valve itself. Almost ALWAYS the plastic piping and hoses to the PCV valve will crack overtime and will lead to a rough idle if the air leak is big enough. Make sure to replace the rubber o ring at the base of the pipe that goes into the front side at the bottom of the engine block. 
Definitely check the purge valve operation as well.


_Modified by GottaSeeThis at 6:36 PM 11-1-2008_


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## roy.vanegas (Jul 24, 2008)

ok, i'm going to do a thorough check of the pcv system this week. thanks.


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## roy.vanegas (Jul 24, 2008)

i found the external area surrounding the pcv breather valve full of grime. when i removed the two connecting hoses to the valve, i found oil in the hoses and at the hoses connection to the breather valve. i've ordered a replacement pcv breather valve and rubber grommet.
someone with a similar problem called car talk, and they too suggested the pcv breather valve. i'll update in a few days, once i've installed the replacement parts.
the pcv breather valve is incredibly difficult to remove. is there a way to remove it WITHOUT removing the upper intake manifold and valve cover?


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## jerrymic (Apr 19, 2007)

*Re: (roy.vanegas)*

have you cleaned the MAF sensor?


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## FL 2.0L (Aug 1, 2002)

*Re: (roy.vanegas)*


_Quote, originally posted by *roy.vanegas* »_
the pcv breather valve is incredibly difficult to remove. is there a way to remove it WITHOUT removing the upper intake manifold and valve cover?


Cut the grommet, which is now very brittle, and replace it for $3 with a new one at Advance auto.


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## FL 2.0L (Aug 1, 2002)

The breather hose may fall apart in your hands when you remove it if it is original. I replaced it all instead of trying to clean it. Well, a shop tore the breather hose to start things off.


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## roy.vanegas (Jul 24, 2008)

*Re: (jerrymic)*

yes, i did a super detailed cleaning, to the point of using q-tips.


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## roy.vanegas (Jul 24, 2008)

*Re: (FL 2.0L)*


_Quote, originally posted by *FL 2.0L* »_
Cut the grommet, which is now very brittle, and replace it for $3 with a new one at Advance auto.

indeed, this is what i was thinking. when i ordered the breather valve, i also ordered a new grommet.


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## FL 2.0L (Aug 1, 2002)

*Re: (roy.vanegas)*

I still broke my pcv, though!
I guess it was before I started cutting...


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## roy.vanegas (Jul 24, 2008)

i replaced the pcv breather valve, and it appears to have solved the P0172 dtc issue. using my scan tool, i put my car through a drive cycle without the code returning, and i'm half way through a second drive cycle.
i'm still, however, getting 
P0440: Evaporative Emission System
P0442: Evaporative Emission System Leak Detected (small leak)
i'm guessing it's the purge solenoid valve and a leak.


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## roy.vanegas (Jul 24, 2008)

i replaced the purge solenoid valve, and it appears to have cleared up the P0440 and P0442 diagnostic trouble codes, but the P0172 code has returned. i have to guess at this point that it is either a faulty injector and/or a faulty fuel pressure regulator.


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## koston. (Aug 20, 2003)

*Re: (roy.vanegas)*

dumbguy: Have you looked at the engine/tranny mounts?


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## roy.vanegas (Jul 24, 2008)

all codes are now clear. the P0440 and P0442 were a result of a damaged purge solenoid valve. i verified this by removing the valve from the car and putting a 9v battery on its contacts. i simulated what the car would do, which is to feed these contacts voltage intermittently. during my test, the valve worked about 95% of the time. if i hadn't taken the valve off to do this check, i would have overlooked the fault, as it was clicking while i checked it in situ.
the P0172 code was a result of dirty fuel injectors. i used a container of techron fuel system cleaner during a gas fill up, then followed the next fill ups with lucas fuel injector cleaner.
i've put the car through 5 drive cycles, and all codes remain cleared. i also passed inspection.
and lastly, i went from about 18 miles per gallon, which i mentioned in the original post of this thread, to just under 30.
thanks to all of you for the help.



_Modified by roy.vanegas at 6:24 AM 12-8-2008_


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## roy.vanegas (Jul 24, 2008)

*Re: (roy.vanegas)*

it's been almost a year since i resolved the issues in this thread, and the car is still error code-free, in case anyone is keeping on eye on this.


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