Engine Performance problem
2000 Other Volkswagen Models 4 cyl Two Wheel Drive Manual 80000 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.

Check fuel pressure see if it is in specs. Also clean MAF and throttle body.

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.

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.

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.

Docfixit wrote:

Check fuel pressure see if it is in specs. Also clean MAF and throttle body.

Can you recommend a good cleaning solvent to use on the MAF and TB?

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

Docfixit wrote:

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

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.

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

Docfixit wrote:

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

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).