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Discussion Starter #1
My wife's 2001 2.0 has been giving me a workout. Just a little history. The Beetle was calling out bad cam position sensor and it also was losing radiator fluid. So I decided to pull the head and replace the headgasket. Replaced the water pump and timing belt, cam position sensor and tensioner. Put the car back together and it ran like a champ the first day. The next day it crapped out and had it towed home. Got on the board and got some help and it was determined that an unrelated problem occurred.

A guy said try cleaning the MAF. I did and the car ran beautifully for a couple weeks and started calling out P0171. I bought a new MAF, installed it yesterday, the car ran good and I gave it back to the wife. After 20 miles or so, it started calling out P0171 - system too lean - bank1.

Not sure what the logical order of diagnosing should be. I replaced the fuel filter about a month ago.

I just test drove it and it seemed a little confused at idle and then straightened out. I took it for a spin and it just doesn't seem to have the acceleration that it used to have. I unplugged the MAF, drove a couple of miles and I think it runs the same without the MAF which I understand makes the computer run on default values.

I am suspicious about the MAF connector. It looks fine, just a hunch. It seems that I am near the problem, just can't put my finger on it.

Don't know where to go from here?

Obie
 

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5/23/10 <3
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Lots of possibilities:

16555/P0171/000369 - Fuel Trim; Bank 1: System Too Lean
Possible Causes

Mass Air Flow Sensor (G70) defective
Intake System Leak(s)

Possible Solutions

Check Mass Air Flow Sensor (G70)
Check Fuel Pressure Regulation
Check Fuel Pump
Check Injectors
Check Intake System for Leaks
Check Exhaust System for Leaks
Check Secondary Air System for Leaks
Check Vacuum Pipes for Leaks

I'd start by checking for leaks. Free and easy.
 

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The computer determines the lamda(which indicates the fuel/air ratio) using the data of the O2 sensor located right after exhaust manifold before catalyst converter. Therefore if the O2 sensor is bad the computer might get a wrong signal indicating lean mixture.

If the O2 sensor data is correct, there is actually a lean condition. This can be caused by either fuel system or intake system. For fuel system, it can be a low fuel pressure which can be caused by a bad fuel pump or pressure regulator, or a leaking injector. This can be identified by measuring the fuel pressure. It can also be a contaminated fuel injector which requires cleaning. For intake system, the common issue is vacuum leak. This can be identified by hooking up a vacuum gauge and see what it tells.
 

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Discussion Starter #5
How do you test an O2 sensor? Just replace it?

I'd like to test the fuel pressure. I don't know if the fuel pressure should be tested before or after the regulator. Do you know the psi values?

Thanks
 

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I don't know whether the O2 Sensors can be VAG-COM tested or not, someone... I didn't see mention of an O2 related code???

Here are the Bentley procedures and pressures for the 1.8T, I'll have to compare the 2.0 and advise -
 

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O2 sensor can be tested but the specified test is not thorough, I mean, it can only test whether the sensor is still working but can't tell whether it's accurate. No O2 sensor related codes doesn't indicate the sensor is working good. Replacing is a good choice if the sensor has been used for very long(Bosch specifies replacement interval of 100k miles). For my AEG engine I searched that the bosch sensor costs no more than $50 on advanceautoparts website after you apply some coupon codes. Similar price on Amazon.

Fuel pressure is tested by unplugging the hose before regulator(that is, the connector located at rear side) and hook up a 3-way connector and the gauge. The specified value is 44psi after you cycle the key a couple of times but keep the engine off(don't crank it), and 39psi when engine idling. Also shut off the engine and see how much the pressure drops after 10minutes. It shouldn't drop too much or there must be an injector leaking.
 

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Discussion Starter #8
Thank you for the help. I will check the fuel pressure first. IF not the solution, I will replace the O2 sensor since the car is a little over 100,000. :cool:
 

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If you have a VAG-COM, you can look at the measuring blocks for the O2 sensors to see if they are working properly.
 

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Discussion Starter #10
Sorry to let this thread fade away. My father died in September and only now is my life returning to normal. We had to take care of mom, get her moved into a condo, empty the big house and get it ready to sell.

So I have just installed some new parts and I am having the same problems.

In summary, this is what I have done to the 2001.

The Bug was eating radiator fluid.
Pulled the head, had it milled, replaced the gaskets and torque her down with new bolts.
Replaced CAM position sensor, tensioner and timing belt.

That all went well. car ran fine then started throwing P0171 - System lean.

Some one the board said clean the MAS. I bought special cleaner , cleaned it and put her back in and it ran great for a couple weeks. No Codes thrown. Then it started again with the P0171.

Bought a new MAS sensor, put it in. Car ran better, but it is not right.

This week, replaced the fuel filter, installed a new fuel regulator and replaced the upstream O2 sensor.

I tried to check for intake leaks. On my old corvette, to check for leaks, you spray Carb cleaner around potential leak areas. If the rpm's change, you found the leak. So, I went around the intake manifold and all the intake hoses spraying carb cleaner and nothing happened.

I reset the codes and drove about 25 miles and it threw the following:

P0171 System Too Lean (Bank 1
P0102 MAF or VAF circuit low input
P0172 System to Rich (Bank 1)

So the only things I know to do are:

1 - check the fuel pressure before the fuel regulator.
2 - check the vacuum

Can anyone tell me what the fuel pressure should be and what the vacuum should be?

Any other ideas appreciated. Not gonna give up on this baby.

Thanks,

Obie
 

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As you have the P0102 MAF sensor input problem, your MAF sensor connector is probably loose. Check it VERY CAREFULLY and open the rear cover of the connector and inspect the wires. I think the MAF sensor loose might caused the too lean and too rich codes. A normal engine never throws out too rich and too lean at the same time.
 

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Discussion Starter #12
I checked the connector. It is not perfect. Some of the red plastic is cracked. I obviously damaged it. But the connections look OK and the wires coming out of the back look good. But I am going to replace it because I am also suspicious about it.

When I cleaned the old MAF, the car responded beautifully for a couple weeks. Then it went south. I put a new MAF and it did nothing.

Just got to if I can find a new connector. Any ideas?

Thanks
 

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Where are you getting your MAFs and what brand are they?
 

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I'm worrying about this too. Here's my self experience: I suspected that my MAF was bad and I bought one remanufactured from advanceautoparts, the brand is A1 Cardone, because I was suffering from hard start problem. However later I found that the real problem was the fuel injector(s) leaking and I replaced all the injectors then the car is good. But after that my car always shows P0172 system too rich and I tried almost all the possibilities and end up with the conclusion that the new MAF was a bad one. I went to advanceautoparts and asked them to replace it for me and they did. Then I put it back on and the problems were all gone. So, don't assume that you bought a new MAF and it's good for sure. Sometimes a new MAF is still bad. I'm now still thinking that the one I traded in for core was still working good and that was a genuine Bosch one.....

Where are you getting your MAFs and what brand are they?
 

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Discussion Starter #15
I bought it from Rockauto and it is a Beck/Arnley. I think Beck/Arnley products are good.

I ordered a new connector from the dealer for $6. Mine definitely is damaged. Not sure if it is the problem. But I will see once it comes in.

Thanks for helping.
 

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I bought it from Rockauto and it is a Beck/Arnley. I think Beck/Arnley products are good.

I ordered a new connector from the dealer for $6. Mine definitely is damaged. Not sure if it is the problem. But I will see once it comes in.

Thanks for helping.
Found this all the way from 2011. It is now 2015 and i happen to have the same problem and figured it wouldn't hurt to ask if anyone ever found out what the problem was?
 

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Discussion Starter #17
Scottyboy,
I did finally fix the problem. I took it to a mechanic I know.
The problem was the MAF. I had replaced the MAF and the MAF connector which did not fix the problem.
The mechanic replaced the MAF with a different product number. That didn't work. I think he went through 3 different MAF'a before he got the right one. Luckily he knew someone who would let him try the mafs with out charging him.

So if I were to do it over again, I would replace the connector if it is suspect and go to the vw parts and have them sell you the proper version of the maf. Apparently there were several versions for that year.
 
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