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2000 Other Volkswagen Models Code PO102 + Rough running engi

Tiny
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  • 2000 VOLKSWAGEN
  • 4 CYL
  • 2WD
  • MANUAL
  • 80,000 MILES
My daughter has a 2000 VW Cabrio with a 2.0 L engine and a manual transmission. I recently replaced the coil on this motor. Some time after, she told me that she was losing power while driving and had to pull the car over. I tried to get it running on the side of the road, but the engine would run extremely rough when RPMS > 2000. So, I had the car towed to my home.

I checked the codes that day and got a PO102 code and PO134 code. The PO102 indicates low voltage on the MAF and the PO134 indicates a bad O2 sensor in bank 1. I decided to clear the codes to see if they would come back. I cranked the car and let it run for awhile. I then increased the RPMS and at about 2000 RPM, the motor ran rough again until the RPMS went back down to idle. Sometimes it would run rough at idle after having brought the RPMS up to 2000 and then return to idle.

The PO102 code did come back immediately after the first warm up cycle. I am waiting to do further warm up cycles to see if the PO134 code comes back.

I understand that, among other things, I am faced with these possible sources of the problem.

Bad O2 Sensor
Bad MAF
Bad CAT
Possible bad MAF sensor or MAP sensor?

At least, that is what I am getting from my self-education on various forums. I do understand that bad MAF and bad O2 sensors are common on these Carbios. However, I am worried about buying the wrong part as each of these parts is somewhat expensive.

Can someone give me some advice here? Is there some way that I can narrow down my search to find the exact source of the problem? Mind you, I am a back yard mechanic with a Haynes manual. I can turn a wrench, replace parts, etc, but am not very good diagnostically.

Thanks.
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Wednesday, July 2nd, 2008 AT 10:46 AM

27 Replies

Tiny
DOCFIXIT
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Check fuel pressure see if it is in specs. Also clean MAF and throttle body.
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Wednesday, July 2nd, 2008 AT 11:14 AM
Tiny
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I found a vacuum hose which was deteriorated and open. I trimmed it and put it back on and the car seems to idle fine at all speeds. I have cleared the codes and will be checking to see if the codes come back. I will then know if I still have a problem.
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Wednesday, July 2nd, 2008 AT 1:44 PM
Tiny
DOCFIXIT
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Great diagnostic work you have elevated the standinof all backyard mechanics.
Tell your friend it looks good runs good I can fix it and its paid for.
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Wednesday, July 2nd, 2008 AT 1:50 PM
Tiny
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Oh well, not so good afterall. I drove the car a few miles and both codes came back. PO102 and PO134 and the car still runs very rough above 2000 RPMs. Drat.

Well, guess I will focus back on the MAF and O2 sensor. Could a code PO102 (MAF) be a secondary result of the PO134 (O2 sensor) code? The reason I ask is, the O2 sensor is less expensive than a MAF so I am willing to replace the O2 sensor right away. I'm not so willing to replace the MAF unless I absolutely have to because I hear that they are expensive.

Also, could a bad MAF sensor (plug) be the source of a PO102 code or is it more likely the MAF?

Thanks for your time.
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Wednesday, July 2nd, 2008 AT 2:31 PM
Tiny
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Can you recommend a good cleaning solvent to use on the MAF and TB?
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Wednesday, July 2nd, 2008 AT 2:35 PM
Tiny
DOCFIXIT
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Maf can cause O2 to set so get some CRC MAF/throttle body cleaner clean both open throttle spray and scrub with a tooth brush any black areas.
Let me know
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Wednesday, July 2nd, 2008 AT 2:51 PM
Tiny
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I'll get the cleaner tonight and will take off the TB/MAF tomorrow after the engine cools. I'll give it a good cleaning. How likely is it that it just needs a good cleaning? Can I expect this to solve the PO102 code?

If the cleaning doesn't solve the PO102 code, what next? Do I need a new MAF? Is that what I should buy or is it a particular sensor, etc?

Thanks for your help.
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Wednesday, July 2nd, 2008 AT 3:58 PM
Tiny
DOCFIXIT
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First we do this carbon can effect many sensors in a bad way so before you start throwing parts we got some stuff to try first. I will be out of town till SAT
Leave me a post and I'll get to on Sat afternoon.
Also if you know where the EGR is take it off clean passages in valve and the manifold.
If I can get in touch with KHLow2008 I'll put him onto you he's good with VW
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Wednesday, July 2nd, 2008 AT 4:31 PM
Tiny
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That will be good. I will locate the EGR in the mean time and give it a cleaning. I appreciate your help.

Is this the EGR? (Sorry, my Haynes manual is practically worthless and the diagram in the engine compartment neglects to mention the EGR in the diagram).


https://www.2carpros.com/forum/automotive_pictures/70282_egrvalve_1.jpg




https://www.2carpros.com/forum/automotive_pictures/70282_diagram_1.jpg

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Wednesday, July 2nd, 2008 AT 5:22 PM
Tiny
KHLOW2008
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Hi wscreate,

Docfixit has requested me to assist and I do not know if I would really be able to.

Firstly, the P0102 code came up first, so it takes precedence over the O2 sensor.

I am not really very familiar with VW so I am not sure if your car is equipped with MAF or MAP.

MAF uses air flow and should be attached to the air cleaner housing through air flows thru it to get a reading. Check for vacumn leakage between the MAF and throttle body. Any vacumn leakage would give a false MAF reading. It is risky to try to clean this as any type of force can damage the sensor. You should try checking the connectors for corroded or bad contacts.

MAP is installed after the throttle body valve and it uses vacumn to provide signals to the ECM.

Check out the above first.
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Friday, July 4th, 2008 AT 6:33 AM
Tiny
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I replaced the fuel filter today. Cleared the codes but they came back (PO102). Engine still runs rough after 2000 RPMS and it bogs down when I try to get RPMs over 2500.

I've done a visual inspection on the vacuum hoses and they all look intact.

I've checked the sensor connections, and they look fine. Hardly any sign of wear and tear. I'm beginning to think that the MAF sensor needs to be replaced. It's an expensive part and I'm not happy.
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Friday, July 4th, 2008 AT 3:19 PM
Tiny
KHLOW2008
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Hi wscreate,

The MAF electrical is definitely giving the problem and if the wirings are ok, you have no choice but to replace it.
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Saturday, July 5th, 2008 AT 6:16 AM
Tiny
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Thanks for the affirmation. I'm going to bite the bullet and buy one on Monday. I'll update this thread once I have it installed.
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Saturday, July 5th, 2008 AT 8:14 AM
Tiny
KHLOW2008
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Hi wscreate,

Hope you have checked and confirm the wiring circuit from ECM to sensor is ok.

Good luck.
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Sunday, July 6th, 2008 AT 12:52 AM
Tiny
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Interesting that you say that. I did check the connector yesterday and found a potential problem.


https://www.2carpros.com/forum/automotive_pictures/70282_connector2_1.jpg




https://www.2carpros.com/forum/automotive_pictures/70282_connector1_1.jpg



So, that concerns me, but I have no idea if the connector is supposed to have 5 metal pieces or 4 with a dummy hole. However, the sensor male plug does have 5 prongs.

As for testing the connection from the PCM to the plug, I have an electrical tester, but have no idea how to use it to test this.


https://www.2carpros.com/forum/automotive_pictures/70282_actron_1.jpg

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Sunday, July 6th, 2008 AT 11:27 AM
Tiny
KHLOW2008
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Hi wscreate,

Check if there are 4 or 5 wires behind the connector.

Some do have dummy points.

If any connector pin is not aligned or is contaminated, it could be having a high resistance thus the wrong reading.

Clean and blow dry it with a contact cleaner or rust remover.
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Sunday, July 6th, 2008 AT 11:51 AM
Tiny
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There are 4 wires behind the connector. The female connectors, two of them are loose and seem out of place a bit. I am not sure if that is creating a problem. I was thinking about finding some dummy wire to plug into each of the connectors individually, and all at once to test the MAF sensor with. In other words, instead of plugging the connector in to the MAF sensor, jump 4 wires from the connector to the MAF sensor. I will also give the cleaning a try.
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Sunday, July 6th, 2008 AT 12:34 PM
Tiny
KHLOW2008
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Hi wscreate,

Any loose connections can result in high or low resistance thereby sending the wrong signal to the ECM.

The MAF is a sensitive item and any slight changes would affect the ECM.

Try to tighten the female clips by compressing the clip area to make them tighter.

After plugging in connector, use a pointed object to push the female clips from behind the connector to tighten them.
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Monday, July 7th, 2008 AT 8:29 AM
Tiny
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Well, I can report some progress. I took the red part of the female connector apart and straightened the metal female prongs. They were bent and after I straightened them, and plugged the connector back to the sensor, the PO102 error did not come back. But, the engine continued to exhibit the same symptoms.

1. Engine idles fine at about 800 rpm
2. When giving the engine gas, it seems to rev fine until about 2000 rpms, and then the engine runs rough and shakes and wants to stall out. In fact, it seems it would stall unless I let up off of the gas.

I ran the codes again after this and found 2 new errors.

P0302 (Cylinder 2 misfire)
P0134 (O2 sensor, bank 1)

The consistent error is the PO134. It has been with me most of the time since the trouble began. The PO302 error is new.

I cleared the codes and ran the car again, and got only the PO134 (O2 sensor) error again.

I guess the question is, can a faulty 02 sensor cause the following problems.

1. Engine stalls, runs rough at RPMs greater than 2000
2. Can a faulty 02 sensor cause a cylinder misfire

Any help will be greatly appreciated. I feel like I am close to solving this problem. I am thinking I should replace the 02 sensor.

Thoughts?
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Saturday, July 12th, 2008 AT 2:24 PM
Tiny
KHLOW2008
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Hi wscreate,

Yes, the O2 sensor can cause the misfire and vice versa. Since the O2 sensor had been there for a long time, I would suggest replacing it.

Misfiring could be due to injectors or spark plugs too but they would not be that consistent and can happen at any rpm.

One more item to check is the EGR valve and the exhaust passage under it. Clogging of the valve and passage will cause misrifing between 1500 to 2500 rpm depending on driving conditions, end result would be a faulty O2 sensor.
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Saturday, July 12th, 2008 AT 11:32 PM

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