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Discussion Starter #1
hi,

I finally got a chance to run a couple of tanks through my 99 2.0/5sp... and just took a road trip so was able to track some 'all highway' mileage too...

turns out I'm getting about 200-230mile per tanks or about 17 mpg +/- which is horrible!

also, at idle with the windows down, the exhaust smell will kill you... probably literally!

I would think bad/clogged CAT but the power on the hwy and around town is great. runs great and hard to keep it at only 70mph.

so will a bad O2sensor cause it to use all of this unburnt fuel? and do these cars have 2 O2 sensors?

its been suggested that it was probably O2 and cat, but I wanted to try the most likely first.

no codes thrown on VCDS btw.
 

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STOP!

Forget all the replacement sensors and parts at this point. Figure out the simple stuff first.

The VERY first thing you need to verify and check it the engine operating temperature. You have VCDS, check the engine temperature. Engine should run about 205F at idle and hold 200F while cruising on the highway.

Exhaust smell is not likely from a bad catalytic converter or O2 sensor but likely due to rich fuel mixture due to a soft failed thermostat. Decreased fuel economy is directly related to reduction in engine temperature.

Also check the Long Term Fuel Trim value at both warm idle and steady cruise 45-55 MPH.

Has the MAF ever been changed? Do not change it, I just need to know the history.

Check the 2nd link in my signature for more info on engine temperature.
 

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Discussion Starter #3
i will do just that...

to my knowledge the MAF has not been changed. but I havent had the vehicle but a couple of months.


ALSO, my AC only works above 2500 rpms or so....could this also be temp or temp sensor related?
 

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Discussion Starter #5
Ok. Values are: temp stayed mostly around 73.5-74C. While Driving. In Stop and go traffic it got up to 84C. Then Back down. Idling in the driveway after driving it finally reached 90C.


Measuring block 032 reads 18.0% for the first lambda and 25.0%for the other
 

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Thermostat is soft, replace it. As I mentioned, engine should run 205F/96C at idle and not ever really drop below 200F/93C.

DO ME A FAVOR, DO NOT DRINK THE PUNCH. In case you read all over the Internet and see all the VW people talking about replacing the temperature sensor, DO NOT DO IT. YOUR CAR NEEDS A THERMOSTAT! Read the Temperature Info in my signature for more details.

VW has WIDE engine temperature error flag in is algorithm and these cars will run 75C/165F all day long without ever triggering a code for the thermostat or engine temperature. The the engine oil gets contaminated in about 2500 miles with water vapor and the 1.8t engines then have their oil pickups clog up, not sure the 2.0l are as bad, but depending on the driving conditions and where you live it could happen.

I dot not know VCDS well, but Long Term Fuel Trim values should not be higher than about +2.5% on a properly operating car.
 

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Discussion Starter #7
Are those the fuel trim values you were asking about?

And would the soft fail t-stat cause the mileage and exhaust issues?

Thanks again
 

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Everything I reference is standard OBDII Fuel Trim values. Long Term Fuel Trim is what I am interested in and can reference as I look at every day and see where "good" cars typically operate.

Yes the thermostat being soft and the engine running so cold will cause the fuel mixture to be too rich, using a lot of fuel and will cause the sulfur smell due to the rich fuel mixture and higher converter temperatures.
 

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Jfoj speaks the truth. I listened to him and changed my stat because I was only idling at around 195F. I went from 17 mpg up to 20 mpg with that change alone. On the highway I can get around 27-29 mpg where I was only getting 20-22 before. He was also the source of my information for changing the thermostat without removing the alternator or anything else. Only took 10-15 minutes to pull the stat out total. That doesn't include time to drain coolant and refill. Took another 10 min to put the new stat and housing in. I would get down on bended knee and kiss him square if I saw him in person. Really saved me a lot of money an time.


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Discussion Starter #10
sounds great. thanks again for taking the time to answer my questions!

when it warms back up this weekend above the 20's at night (in alabama!!!) I'll swap out the t-stat.

thanks for the tip on not removing the alt. i wondered about that.


is 'lambda' the same as 'fuel trim'? i'm new to vcds myself.
 

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Discussion Starter #11
i changed the thermastat...really easy and quick on these cars.

immediately i noticed the heater works much better and quicker.

I 'think' ive noticed a slight improvement in the exhaust smell but its still there more than it should be.

and havent run enough gas through it to see if the mileage is up.


Do i need to go in and clear any values out or should the exhaust/lambda issues eventually right themselves?
 

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Discussion Starter #13
ok.... changed the tstat and it seemed slightly better...

had a chance to grab and temp sensor and o2 sensor from pullapart so threw those on too...and it seems to have cleared up the problem.
 

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Did your car smell kind of like rotton eggs? And how long would it take until your heater would start working at a cold start? My 99 smells bad after it warms up and it takes like 8-10 minutes until my heater starts to blow warm air.

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Did your car smell kind of like rotton eggs? And how long would it take until your heater would start working at a cold start? My 99 smells bad after it warms up and it takes like 8-10 minutes until my heater starts to blow warm air.

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Rotten egg smell is a classic symptom of a bad converter.

Taking to long to get heat in the car is a symptom of a bad thermostat in a lot of cases.

Maybe the two are related? Car can't get up to correct temp--it regulates itself 'richer' with the fuel mixture.. (Long term fuel trim would reveal) And it over "gasses" your converter to the point it breaks down.

Coincidence? I wonder......

S-
 
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