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Discussion Starter #1
Alright, I've looked through the forums as much as I could and can't find anything to the severity of the issue I'm looking for. (I can find ones with mileage in the high teens, but none this bad) On average, the Beetle (1999 2.0 AEG 109k miles) has lately been getting near 10 mpg when filled up.

The mileage issue has been present since purchase of the car back in October, granted it was a bit higher (12mpg average)but I can attribute the loss to winter blend gas as well as driving style.

To my current knowledge, there are only two DTC's present (I printed them out a couple weeks ago when I had the Bug in my garage to replace a wheel sensor):

P1128 - Fuel Trim Bank 1 (Mult) System too lean

P0341 - Camshaft Position Sensor (G40) Implausible Signal Intermittent

I'll scan again for codes Tuesday when I get a chance, to make sure these are the only ones still.

Could either of these codes (alright I know its probably, no definitely related to them) be causing the issue, and more importantly how can the issue be corrected? The mileage is so bad that it is honestly more economical lately to drive my lifted Grand Cherokee with it's V8, hah...

I suspect from some research that the P1128 could be corrected with O2 sensor replacement, but I'd like a somewhat more definitive answer before money starts to get thrown around at the issue.

I should probably also mention that the car is running fantastically, or at least it isn't bad. It doesn't surge, it doesn't start difficultly, etc. As far as I can tell it's running fine.

Air filter is clean, well clean enough, it's been in there for about 2k miles, but it's no where near needing replacement.

Spark plugs and wires were done (as shown by records from previous owner) at 102k.

As I look through these records now, it seems that at 106k the Fuel Filter as well as Downstream O2 Sensor (I think, I can't read this mechanic's writing) were also replaced.

Thanks guys and gals :D
 

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5/23/10 <3
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Here is some info for you:

17536/P1128/004392 - Ross-Tech Wiki
17536/P1128/004392 - Fuel Trim; Bank 1 (Mult): System too Lean
Possible Symptoms

Malfunction Indicator Light (MIL) active

Possible Causes

Mass Air Flow (MAF) Sensor faulty
Oxygen Sensor Control faulty
Oxygen Sensor(s) faulty
Fuel Injector(s) faulty

Possible Solutions

Check Mass Air Flow (MAF) Sensor
Check Oxygen Sensor Control
Check Oxygen Sensor(s)
Check Fuel Injector(s)
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16725/P0341/000833 - Ross-Tech Wiki
16725/P0341/000833 - Camshaft Position Sensor (G40): Implausible Signal
Possible Symptoms

Malfunction Indicator Light (MIL) active

Possible Causes

Wiring from/to Camshaft Position Sensor (G40) faulty
Camshaft Position Sensor (G40) faulty
Timing misaligned

Possible Solutions

Check Wiring from/to Camshaft Position Sensor (G40)
Check Camshaft Position Sensor (G40)
Check Timing

--------------------------
A bad O2 sensor can affect your mpgs but shouldn't drop it that low. 10mpg is at least half of what you should be getting around town, easy. I got 22-23 around town in my 2.0. I never got below 21mpg, and that was when I had a bad O2 sensor.

Did you buy this car private party or from a car lot? You should have brought up the poor fuel mileage after you purchased it. 12mpg SHOULD NOT happen if the car is healthy. You can drive it aggressively but you won't get much under 20 if at all. You definitely have an issue going on.

Has the timing belt/water pump been replaced? If not, you are on some serious borrowed time.
 

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LOL, Are you sure you are not driving a Hummer instead of a Beetle? :p There is no way your Beetle is only getting 10mpg without some signs of drivability problems. Perhaps there is a leak in the fuel tank? Do you smell fuel at all? Is your car smoking like crazy? There have to be some symptoms to justify that type of gas mileage.
Perhaps you have some leaky injectors? Next time you prior to filling up pour in a can of "Seafoam" That stuff is great when it comes to cleaning dirty injectors. As Smileybug already mentioned a faulty O2 sensor or MAF sensor can contribute to gas mileage issues but I have never heard of a Beetle getting 10mpg. Heck a Hummer gets more than that.
Check the gas line and tank for any punctures or leaks. Take a look at the injectors and see if there is any moisture that you can detect or any fuel that you can smell. Something is definitely not right. My Beetle has 160+k miles and it still gets an average of 26mpg. Worst I have gotten was 23mpg and that was mostly city driving.

Good Luck and Keep us posted!

PS: Ditto on the Timing Belt service. If that belt goes your gas mileage problems are over. ;)
 

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Discussion Starter #5
SmileyBug said:
A bad O2 sensor can affect your mpgs but shouldn't drop it that low. 10mpg is at least half of what you should be getting around town, easy. I got 22-23 around town in my 2.0. I never got below 21mpg, and that was when I had a bad O2 sensor.

Did you buy this car private party or from a car lot? You should have brought up the poor fuel mileage after you purchased it. 12mpg SHOULD NOT happen if the car is healthy. You can drive it aggressively but you won't get much under 20 if at all. You definitely have an issue going on.

Has the timing belt/water pump been replaced? If not, you are on some serious borrowed time
Private party, and we weren't aware of the mileage issue until weeks after purchase when it was finally filled up. Yes the timing belt and water pump were replaced at about 75k miles.

IndyTom said:
LOL, Are you sure you are not driving a Hummer instead of a Beetle? There is no way your Beetle is only getting 10mpg without some signs of drivability problems. Perhaps there is a leak in the fuel tank? Do you smell fuel at all? Is your car smoking like crazy? There have to be some symptoms to justify that type of gas mileage.
Perhaps you have some leaky injectors? Next time you prior to filling up pour in a can of "Seafoam" That stuff is great when it comes to cleaning dirty injectors. As Smileybug already mentioned a faulty O2 sensor or MAF sensor can contribute to gas mileage issues but I have never heard of a Beetle getting 10mpg. Heck a Hummer gets more than that.
Check the gas line and tank for any punctures or leaks. Take a look at the injectors and see if there is any moisture that you can detect or any fuel that you can smell. Something is definitely not right. My Beetle has 160+k miles and it still gets an average of 26mpg. Worst I have gotten was 23mpg and that was mostly city driving.
There is no driveability issues that I can tell, but I really don't have anything similar to compare it to, (aka another Beetle). It doesn’t seem strained for power, it doesn’t have issues starting, etc. I don’t smell fuel, I thought of the tank possibly leaking, but when I looked/smelled, couldn’t detect anything. Smoking… a bit I guess, I wouldn’t call it crazy? But it is winter here and cold in Western NY.

Already did Seafoam it, that was one of the first things I did after purchase. I’ll take a look at the injectors tonight or tomorrow and see if I can find any wetness there.

D2Beetle said:
A bad CAT can have a significant affect on gas mileage. Considering the rear O2 Sensor is part of the CAT, you might want to take a look at it.
The thought of a clogged CAT crossed my mind, as a buddy of mine had an S-10 with the 4cylinder and was getting ~8mpg before he replaced it and then bumped right up to 20 after.

Another thing that crossed my mind last night as I was thinking about this, was the possibility of the fact that it is primarily used for very small journeys (less than a mile sometimes), meaning the O2 sensors would be stuck in open loop mode. But I can’t imagine that causing that much of a decrease. (And don’t chastise me for the short journey’s, I’m not the one making them in it, the girlfriend is and she works around the corner from her house).
 

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You do have an AEG, which has a very failure prone cat. The innards come apart. But you *should* hear it rattle, and if its that bad, you *should* also have a code for it (p0420).

Short journeys still wouldn't net you 10mpg. I drove my car less than 5 miles for a lot of the time while I was in college (I got some highway drives once or twice a month, but most driving was around town). Still got 22-23mpg. That won't kill your mileage like that.
 

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Discussion Starter #7
SmileyBug said:
You do have an AEG, which has a very failure prone cat. The innards come apart. But you *should* hear it rattle, and if its that bad, you *should* also have a code for it (p0420).

Short journeys still wouldn't net you 10mpg. I drove my car less than 5 miles for a lot of the time while I was in college (I got some highway drives once or twice a month, but most driving was around town). Still got 22-23mpg. That won't kill your mileage like that.
I'll get under there and rattle it by hand either tonight or tomorrow, but like you said, shouldn't the downstream O2 be picking it up if the CAT isn't doing it's job?

And on the note of short journey's, I didn't think it could have such a drastic effect, but I figured I should mention it just in case anyone knew something.
 

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5/23/10 <3
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You are getting a code for an O2 sensor.

I think if you could get the car hooked up with VAG-COM, it would tell you a lot...
 

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SmileyBug said:
You are getting a code for an O2 sensor.

I think if you could get the car hooked up with VAG-COM, it would tell you a lot...
Like I said when I get a chance later or tomorrow I'll rescan to see if the codes have changed since last time I scanned.
 

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Are you using VAG-COM or a generic code reader?
 

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Just went and scanned for codes again, same two present as above. Didn't check the CAT or anything else as its cold and raining/snowing out.
 

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Use VAG-COM and monitor the O2 sensors. That can tell you if they are working properly. Don't think you can get any readings off of the cat, but you can do a lot of troubleshooting with the VAG-COM.
 
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