Power surge on acceleration

[Stan TDI]

I have a 1997 TDI that was purchased in Canada. I moved to the US about 3 years ago and started having issues with the TDI. There are 2 issues: if I accelerate hard I find that I have a power surge (almost to the point of bucking) around 2800 to 3400 RPM; and, sometimes after a warm start, you can be putting out of a parking lot at say 15 RPM and it feels like I lose power and start to blow a lot of smoke. I never had any of these problems in Canada and think it may be fuel related. Or maybe my car is just showing its age? The USA technicians think it is carbon. The Canadian technicians say carbon is not an issue in the year and it is likely something else. All comments are greatly appreciated!!!

 

[jck66]

What color is the smoke? Does the car run roughly when you are at 15 MPH (I assume this is what you meant) in a parking lot? I'm going to guess unburnt fuel due to a periodically clogging injector. When was the car's last fuel filter change? Please, somebody with a bigger brain chime in!

 

[20ValveT]

I would start by making sure your N75 valve is working properly. Periodically they get a bit gummed up.I don't think you have a carbon issue seeing as when the intake starts to get plugged you lose power in the higher RPM range, not the lower. Inspect all your vacum lines black, red, and blue, there may be a small leak. Check the MAF also, these cars really didn't have a problem with MAFs, but its still a possibility. Anyways hope this helps. Good Luck

 

[Stan TDI]

Thank you for your replies! Here is some additional information: the smoke is blue and the message should have read "about 1500 rpm". Also, it is prevalent when I accelerate and then back off of the gas. Still keeping some pressure on the accelerator. It almost feels like the cylinders get flooded with fuel. Press on the accelerator and it all goes away.

I appreciate the comment about carbon. The dealer is convinced of this and wants me to spend $500 to get it cleaned.

 

[weedeater]

blue smoke = oil. How's your oil level? However it could be a leaking injector...

 

[Stan TDI]

Thanks weedeater! I did have my injectors checked and apparently they are fine. Oil level seems fine and this is an intermitent problem.

BTW...fuel filter has been replaced within the last 20-25000 KMS or about 1.5 years ago. I was thinking of replacing it...just in case. Comments anyone?

 

[Stan TDI]

I am having some service done this weekend. I will have the N75 checked. Since this is a relatively cheap part, should I just ask them to replace it or is it easy for them to test?

Thanks for all of your help!

 

[20ValveT]

If the N75 is Gummed up just use some carb cleaner on it. If its not functioning properly then replace it.

 

[Stan TDI]

I had the N75 checked and it is apparently fine. I also changed the air filter since it was about time. I still see the problem but it is less promounced. This is most noticeable when merging onto the interstate in 3rd gear with the pedal to the metal. Any other suggestions on what I should try?

 

[Drivbiwire]

The N75 will not throw a code when it starts to go bad. The best way to check it is to install a good one and test drive it. You could also do some data logging and look at the boost control delay deviations.

So how did they check it anyway? and who is they?

DB

 

[Stan TDI]

Thanks for your reply Drivbiwire. I had my car in to the dealership for some maintenance and asked them to check/inspect/clean the N75 selenoid. They told me this was done and it was fine. I am not as technically proficient as many other members so I have to rely on other people. So you are saying that I should ahve it replaced "just in case"?

 

[SevilleSharan]

I have changed N75. I have not performed any real testing yet as I need to drive the car for at least 200M to feel somewhat confident on having fixed the problem (well after 10K I will be even more confident).
Anyhow after changing the N75 I monitored the MAF preassure and now meassured MAF preassure seems to follow theoretical MAF better than before. I think this looks very promising.
Anybody has had a similar experience?

 

[SevilleSharan]

I mean admision preassure not MAF (of course).

 

[Stan TDI]

An update...I recently installed Upsolute chips in my A3 and this problem has magically disappeared! I do not really understand why but I am not complaining. These chips make for a really nice ride!

Thanks to everyone for there troubleshooting tips!

 

[WillR]

Where besides the Stealer are you folks buying the N75?

Mine has has this high speed power pulse or low power on and off for about 2 years now.

About the N75 and the CEL. All this winter when it gets below 20 deg F out, I hit the highway just after the temp gauge hits 190, as I pull through the on ramp the car will be running good, no pulsing of power, then all of a sudden the car will "let up" power, kind of like something slid under the fuel pedel. I hook up the VAG-com and find an error (forget the number) about pressure not as expected. This morning it set 2 times on the highway, restart the car and it runs great again, then the 3rd time it set the CEL came on! I had the VAGcom hooked up by then and yes, it was the same code.

How much is the valve? It might we worth just replacing it instead of cleaning it.