Intermittent engine power loss

05-20-2005, 09:32 PM
I have a '99 Jetta TDI that first suffered from sudden loss of engine power in 2002. The service guys told me that they could not find anything wrong, but a week later the check engine light came on so I took it back. They worked for 2 weeks trying to figure out what was wrong, and in the end said that they "tightened the timing belt by a notch". The car was fine for 2 years, then it started again. I have since had the engine decarboned, then the MAF replaced but the problem continues. What is happening is that only very occasionally I will shift (manual tranny) and the engine will only slowly speed up for several seconds despite my having the accelerator fully depressed. Then suddenly it will "kick in" and the thing takes off like a shot. This will occur for a few shifts, then it will be fine for a couple of weeks before doing it again. The service guys can't find anything wrong, and state that it needs to be connected to a sensor to tell what the problem is. After leaving the car with them for a week (it behaving beautifully the whole time), I'm at the end of my rope. Plus tired of spending a few hundred $ each time only to have the same problem at the end. Please help!!

05-22-2005, 11:07 AM
What code was set w/the CEL coming on? It sounds possibly like the N75 valve that controls turbo boost pressure is sticking. First check all the vacuum hoses that run from it (located on fenderwell next to air filter housing).

05-22-2005, 05:06 PM
I actually have no idea what code appeared with the CEL back in 2002. It's a long story, but in the end I did not get a copy of the work oder, so all I have is what was told to me verbally. Originally the VW service people though it was the fuel pump, but then said that the timing belt was what needed tightening (whatever that means).
In October, I had the engine decarboned (which is what was recommended), which did make the problem occur less frequently (every two weeks instead of daily).
In February, the CEL came on again (intermittently), and I was told that it was the MAF, so that was replaced. There is no code # on the work order - it simply states that they retrieved a sporadic MAF sensor code. It also states that the MAF would not fail for them, but I asked them to replace it anyway hoping that would solve the power loss problems. It didn't.
The latest idea is that it is the turbo solenoid sticking, however the service manager states that the CEL should be lighting if this is the case (and it is not). Is the solenoid the same as the N75 valve? I was told that a chemical cleaning of the engine would clean the turbo. I had a manual cleaning of the engine back in October, however the service manager states this would not have cleaned the turbo because they can't take it apart. What are your thoughts on this? At $150 for the chemicals + 3 hours labour, this will be another $300+ bill.
In the meantime, I will check the vacuum hoses. Thank-you for your assistance!

05-24-2005, 03:50 PM
I don't think it will help to have the cleaning done.
how many miles on it? usually if the timing belt slips the engine will run real rough. check your vacuum lines like boschmann suggested.
also if your CEL comes on again take it to an autozone or a similar store and have them read the codes.

05-25-2005, 03:59 PM
Remove the intake air boot right at the aluminum manifold & look inside to see if it is restricted with carbon buildup, I don't reccomend the "chemical" cleaning, just break it all up & vacuum it out. The N-75 could definitely be the problem, from what I've seen usually it will set a VAG 00575 code for intake manifold control pressure (no associated "P" code). Valve is about $60 from the dealer & you can install it yourself.

06-10-2005, 06:15 AM
This very exact same thing happened to me. You crank the engine and its fine. A few minutes later WHILE driving the engine totally starts to cut off randomly, then finally shuts off. Sometimes it won't crank at all.

I brought mine to the dealer and they said they fixed it by chaning the main computer. Five minutes from the dealer it failed again. Sputtered out like it ran out of gas or something. 2 weaks later they said they found the problem. Run this by your dealer to see if they can check it out.

Their was a cable they found that linked the ignition to the transmition or something. They said it was loose or broken. They replaced and it has been fine so far...and that, believe it or not, was also around the same time you had your problem. in 2002. My car is also a 1999 new style Jetta. Coincidence?

Anyway, go to the dealer and have them check the wiring. Somewhere in the ignition area.

06-11-2005, 08:13 PM
Well, I have much to update on now which may be of importance to others with Jetta problems...
I have recontacted the Jetta dealer that serviced my car when it originally had a problem in 2002. Apparently, it was the timing belt on the fuel pump that they had to tighten. With a total of 2 weeks at the dealer where I live now on my latest visit, I have been told the following: 1) it is not a problem with the fuel pump (although nobody could explain how they know this to be so); 2) whatever this chemical cleaning is, it cannot be done on the older style Jetta (even though this is what had been recommended to me by them) as it eats gaskets; 3) my MAF needed replacing again even though it was not failing, the CEL was not turning on, and it had just been replaced back in Feb; 4) my coolant thermostat was not working properly and needed to be replaced (although this in the 5 weeks previously spent at the dealers had never been found to be a problem, and, quite frankly, I don't see how this would suddenly make the engine lose power intermittently for only a few seconds and only when shifting); 5) VW will replace MAFs for free if you are the ORIGINAL owner only, up to 115,000 km/70,000 mi (not for me - I bought the car used; begs the question why who owns the car should matter on a extended warranty on a part).
Anyhow, I found the ultimate solution to my problem - I sold the car. This has been a very disappointing experience. I will not buy a VW in the future, which is too bad (at least for the dealership) - the next one I wanted was a Touareg... Good luck to the rest of you, and thank-you for all of your advice!

06-13-2005, 03:36 PM
too bad you had such a bad experience with the dealer.
My dealer so far has bin good to me, just goes to show you that the people running the dealership make the difference.

06-15-2005, 03:07 AM
Sad to hear that sold your TDI, but their service has been known to have that effect. If I relied on the dealership for service, I probably wouldn't keep mine too long either.

Out of curiosity, did anyone try cleaning/replacing the MAF connector(not the sensor itself)? What about cleaning the "snow screen?"

Also, what did you replace the TDI with?

06-20-2005, 11:06 PM
I am not aware that anyone checked anything but the MAF itself. Incidentally, the MAF has now been replaced a total of 3 times, the first being at the time of my initial problem in 2002, then again in Feb this year, and now in May. It would not surprise me one iota if it were a line leading to the MAF, or something equivalent, that was getting plugged up and not the MAF itself. The service managers recommended this "chemical" cleaning, which apparently gets into little nooks and crannies (such as the turbo) that they can't physically clean. They then told me that they couldn't do it on the older style '99 Jetta because the chemicals eat up one of the gaskets (not sure which one). Their final word was that "some cars just like to chew up the MAFs", thus frequent replacements are necessary (but every 3 months?! please!)
I decided to return to my family tried and true - a Honda. My kids were getting far too big for the Jetta now anyway, so we went with an Odyssey. And we're loving it! And, as was mentioned, service is the key. Honda's service is excellent. They don't try to side-step my questions, but describe the mechanical workings of the vehicle in as much (or little) detail as I require. The only downside compared to the Jetta is the cost of fuel, but with the VCM (3/6 cylinders shut off at cruising speeds), the cost hasn't been too terrible.

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