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VW MKIV-A4 TDIs (VE and PD) This is a general discussion about A4/MkIV Jetta (99.5-~2005), Golf(99.5-2006), and New Beetle(98-2006). Both VE and PD engines are covered here.

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Old October 1st, 2003, 19:10   #1
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Join Date: Mar 2002
Location: MN
Default Momentary Power Loss Above 3000 RPM

My car seems to be acting strange for the last couple of weeks, and I haven't been able to figure it out. Hopefully someone has had these symptoms before and can diagnose this...
Well, the car starts and runs fine, but quite often when I rev above 3000 RPM between gears, the motor seems to cut out for a second or two, then resume. When this happens, the boost drops by about 5 psi, and it feels similar to hitting a speed limiter like on a domestic car, where the ECU shuts the motor down until you drop below the governed speed. It seems to happen more in the morning when it is cold, (been 32F here for the past couple mornings), but has happened when warmer also. No CEL ever generated when this happens.

127,700 miles on the car. Engine mods done to the car- Upsolute chip, PP520 nozzles, EGR "tuned" and totally disconnected (with no CEL ever), and Boost Valve set at 21 psi. TB, water pump, coolant, thermostat, and fuel filter changed recently at 120,000 miles. Turbo was new at 116,000.

Things I have tried to solve the problem-
1. Replaced factory MAF (yes it does have 127,000 miles on it) with my spare Pierburg. Didn't fix problem.
2. Tried switching N75 and N18. Didn't fix the problem, so switched back.
3. Changed "T" on top of the fuel filter with spare. Didn't fix the problem.

I have monitored it with Vag-Com, and cannot seem to find anything unusual. I am really stumped.

My next thought is the MAP sensor in the intercooler, may be sensing too high of boost and is triggering something, but I would think that may generate a CEL. I don't have a spare, and don't want to buy one if I don't need it.
I don't think it would be the turbo linkage being gummed up as there is only about 10,000 miles on it.

Does anyone have any other suggestions as to what it may be?

Any help would be appreciated. I am scheduled for the dyno on the 12th, and I don't want it cutting out like this when it is on there, so I hope to have it fixed.

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Old October 1st, 2003, 19:30   #2
Gary Miyakawa
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Join Date: Feb 1999
Location: Roswell, Ga
TDI(s): 1998 NB TDI
Default Momentary Power Loss Above 3000 RPM

Check for a vacuum leak in the N75 circuit...

Gary M
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Old October 1st, 2003, 22:18   #3
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Location: Walnut Creek, CA
Default Momentary Power Loss Above 3000 RPM

It could still be the MAF. Test it with a factory Bosch before ruling it out completely. Under some conditions, the Pierburg causes a different behavior, seen it on a few cars now.
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Old October 2nd, 2003, 05:50   #4
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Join Date: Mar 2002
Location: MN
Default Momentary Power Loss Above 3000 RPM

Thanks for the replies.

I will check out the full vacuum circuit of the N75 and also try without the boost valve hooked up.
I will also see if I can borrow a good Bosch MAF for a day or so to check that out.

Danix- Do you still sell Bosch MAFs? If so, for how much and do you have any in stock?
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Old October 3rd, 2003, 01:05   #5
Join Date: Jun 2000
Location: New Westminster, BC, Canada
Default Momentary Power Loss Above 3000 RPM

twojettas - I've been having almost the exact same problem with my 2000 Golf GL...I don't have any ideas as to what the problem is either...please keep us posted on your diagnosis of this!
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Old October 24th, 2003, 17:27   #6
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Join Date: Mar 2002
Location: MN
Default Momentary Power Loss Above 3000 RPM

Well, I received my new MAF from Danix a couple weeks ago and put it in, (thanks for the quick service Dan!). Everything seems to be normal again, and it hasn't done the strange power loss since. However, it also hasn't been as cold here since the time when it was acting up...
Overall, I think the new Bosch MAF makes the car work a lot better than the Pierburg ever did. Power is much more linear and smooth. Even though the Pierburg is half the price, I will definately opt for a new Bosch should/when I have to replace it again.
I even pulled my best mileage ever with it on a trip last weekend, 51.5mpg. And that was cruising at 85 to 90 MPH most of the time, for a 300+ mile, each way, road trip!

I was able to get it dynoed with the new MAF. I pulled 138HP and approx. 270 for torque, (torque was calculated using wheel speed since they did not have the optical setup ready to go that day for getting the RPM).
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