please help, boost problems

I have a 90 tsi awd and its acting wierd. When I start it up, it will seem normal, idling at about 1800rpms til its warm and my boost guage will read boost. But after about 3 minutes, it wont read any boost, only vacuum. Then it will just not move at all and stay at about 20 vacuum. My guage is hooked up correctly and I have swapped another working guage in and had the same issue. I've tested for leaks and fixed the seals on my throttle body shaft but still have the same issue. I'm two hours away from home in college and its killing me in gas to try and fix it. Any help is appreciated.

Well, I'm not sure about your car, but mine will go up to about 1500 rpms at start up and then down to 1000. Once it warms up it's at 750-800. Mine stays at around -20 vacuum all the time at idle. When i step on the gas it usually goes to 0 vaccuum and boost. Around 2300 rpms is where i start seeing boost. This is with a 16G.

What you have described sounds normal, according to my car. The bad gas mileage may be due to something else. Any CEL's, or weird readings on your data logger?

How long has the problem been doing this, or has it been doing it since you got the car/installed the gauge? It may be hooked up wrong.

When I first start it up and drive I will see about 5psi of boost max. Then after about 3 minutes of driving, I won't get any boost at all and the guage will read 20 vacuum and not move no matter what. I don't have any CEL's, the only odd ready on the logger is when at WOT, my o2 volts is always .02 or .00 From what I have heard and read, at WOT the o2 volts should be much much closer to .90 Oh and I'm getting some knock too. I'm not getting bad gas mileage that I know of, because I haven't drove this car much at all, I've probably put 200 miles on it since I bought it in Febuary. I just have to drive home to work on it.

Ever since I got my guage installed I have had this problem, but I may have had it before because the stock guage is only an estimate from the ecu. I have tripple checked the installation of the guage, I put it in based on what I see from this sketch. http://vfaq.com/index-main.html thanks

Thanks for input.

Does the boost gauge correlate with how the car is acting? ie. You step on the gas and the car takes off but the boost gauge goes crazy, or you step on the gas and the car has no boost? Sounds like you have more than just one problem here, and I think they're all working together to really mess things up. When was the last time you did a tune-up?

When I step on the gas right after I start it, the car goes and the gauge will move and seem normal, from an idle of about 20 vacuum to boost of about 5psi. But after 3 minutes, I can floor it and it will stop showing boost and only vacuum. It acts like its stuck at 20 vacuum, but I know its not the gauge itself because i tried a different one.
Thanks for input.

What consists of a tune up?

Does the car have a boost controller?

A tune up consists of the following for the most part:
Replace the fuel filter
Change the spark plugs and examine wires
Adjust the ignition timing.
Check belts.
Check fluids under the hood and replenish.
Replace the air filter
Adjust the clutch.
Check the battery

Have you done a boost leak test ever?

I do have a boost controller, but it has not been installed.
I have swapped the wires and spark plugs.
I have checked the belts and fluids.
I just installed a new clutch.
I just got a new battery.
I haven't messed with the fuel filter, ignition timing, or got a new air filter.

I ran the boost leak test and only found the leak at the throttle body. I have since then fixed it and found no other leaks.
Thanks

I'm just reading over your posts and you never say if it's effect performance (atleast that I can see) or if it's purely the guage itself. IE When the guage is reading just VAC is the car lacking alot of power? Or is it running like normal and the guage is the only thing messed up?

It sounds more like a gauge problem. Is the gauge mechanical or electric? If its mechanical you might want to check the vac hose that goes to it. I know that if I twist my boost gauge just a little the line hits the pod and it wont read right. It will get stuck in vac or not go over like 10.

Well I don't know for sure. Since I have bought it in February, I have only put about 200 miles on it and it hasn't changed any in how it drives. It seems fine to me, I can feel it pull harder around 3k, but then again I haven't rode in a stock turbo dsm. I'm going to say the gauge is mechanical.....it uses vacuum line. I don't have the gauge mounted because the problem first occurred when it was mounted so i unmounted it to swap a different one and to check the connection. If the line was messed up though, the gauge would not just work for the first minute or so and then stop working because the line was messed up would it?
Thanks

Well I don't know for sure. Since I have bought it in February, I have only put about 200 miles on it and it hasn't changed any in how it drives. It seems fine to me, I can feel it pull harder around 3k, but then again I haven't rode in a stock turbo dsm. I'm going to say the gauge is mechanical.....it uses vacuum line. I don't have the gauge mounted because the problem first occurred when it was mounted so i unmounted it to swap a different one and to check the connection. If the line was messed up though, the gauge would not just work for the first minute or so and then stop working because the line was messed up would it?
Thanks


Not necessarily.

On my old DSM GST I had a POS guage on it, and often it would do pretty much exaclty what you were describing. The problem was that the vac line that went into the back of my guage wasn't seated proberly. When I would first start the car the guage would be fine, but after a few minutes of running (and subsequent vibration) The guage would drop and read nothing.

I highly suspect the problem lies in the vac line itself. Either it's not seated on the guage or on the T or there is a leak somewhere in the system.

If there was a major leak in the system the car would be very slow and sluggest. Since you are telling me that the car responds and pulls harder at abotu 3k. (about max spool for the stocker) It leads me to believe that you may be fine to drive the car around like normal. I just wouldn't install any mods until you can get the guage figured out.

Ok but what do you think about my logger showing .02 for the o2 volts when at WOT? This website says it should be in the upper 25% http://www.pocketlogger.com/index.php?pid=params&param=o2&type=dsm

Should I get a new sensor?

Ok but what do you think about my logger showing .02 for the o2 volts when at WOT? This website says it should be in the upper 25% http://www.pocketlogger.com/index.php?pid=params&param=o2&type=dsm

Should I get a new sensor?

This could be a problem unrelated. Usually a bad O2 Sensor will throw a CEL but not always. The symptoms you are describing do not sound like an O2 sensor problem to me. But what the problem with your O2 sensor is, I don't know. I'm sure someone else here may be able to enlighten you.

There are two O2 sensors, one on the O2 Housing off the turbo and the other behind the cat. Are you logging from the O2 sensor in the front or back?

I don't put much faith in the stock O2 sensors. The only way to get real good readings is to use a wideband O2 sensor.

I'm not sure which sensor I am reading from. I thought the 1g didn't have the second sensor, only the 2g's did. I will have to look into that. Thanks a lot for the help.

did you boost leak test it beyond the psi your car is rated at? if so you should see the wastegate start moving. if it doesnt, or if it somehow got damaged, it will let all boost get by. this wouldnt cause your idle to do that though. a high idle at start is usually a vaccuum leak, possibly electrical. o2 could have affected this

When I tested it the first time I had a better compressor and I tested it until the wastegate opened, which was around 10psi. Yeah I think I'm going to try and get a new o2 sensor that goes in the o2 housing. Any suggestions on where to buy a good one from? Thanks