02 Jetta has boost, then doesnt

[jbruAT09]

Hey all,

About a two weeks ago i ran the car for 5-10 minutes and it was acting strange, wasnt boosting. the next two weeks it ran fine.
Two days ago i ran the car for 5 minutes to work and it ran fine. On the ride home it had no boost. This morning it had no boost. I ran the car after sitting for 2 hours and no boost. After a red light i started driving and the boost was back. Shut the car off for 6 hours, drove it back to work with boost. It sat for 15 minutes until i drove back home and had no boost. Thoughts? i plan to get codes read tomorrow whether or not its boosting again.
Im thinking a vacuum leak would result in the boost not returning, i may be wrong but im thinking the N75 or the actuator arm? just thought. i noticed another recent post and the MAP was to blame.

Thanks
220k

 

[yatzee]

sounds like you're going in and out of limp mode. Do a quick search - common issue. Lots of threads about it.

The faults will help you diagnose the issue

 

[honda_vtec2]

Hey all,

About a two weeks ago i ran the car for 5-10 minutes and it was acting strange, wasnt boosting. the next two weeks it ran fine.
Two days ago i ran the car for 5 minutes to work and it ran fine. On the ride home it had no boost. This morning it had no boost. I ran the car after sitting for 2 hours and no boost. After a red light i started driving and the boost was back. Shut the car off for 6 hours, drove it back to work with boost. It sat for 15 minutes until i drove back home and had no boost. Thoughts? i plan to get codes read tomorrow whether or not its boosting again.
Im thinking a vacuum leak would result in the boost not returning, i may be wrong but im thinking the N75 or the actuator arm? just thought. i noticed another recent post and the MAP was to blame.

Thanks
220k

A few things you can do/check...

Scan with VCDS, do some turbo/maf logs to see how your car is behaving.
Inspect all the vac/air lines for leaks.

I had a similar issue like yours with an mk4 i picked up this past summer. Only started acting up in the cold weather. I scanned the car and no codes were revealed. However, car would over boost from time to time. Other times boost would be sporadic such as your symptoms. This is what i did to temporarily fix the issue. I grabbed a 13-15mm wrench and put it around the actuator lever on the turbo and exercised it numerous times in full range motion (up/down). That freed up the mechanism. I've noticed these turbos tend to soot up. I also tested the diaphragm and adjusted the boost so it spikes up to 16psi and levels out around 12. Normally it would spike up to around 22 and level off around 18. So i plan on removing it in warm weather and cleaning it out.

good luck

 

[TimDI]

Unplug your MAF sensor will drive fine without it and eliminate that as your cuplrit. Had the same problem once unpluged car drove fine for the 400km drive back home where I fixed it.

 

[jjcsnlynn]

I wonder if it could be the wastegate shaft sticking.

 

[Enabled]

Check engine on or no?

Any broken or disconnected vacuum tubing?

 

[jbruAT09]

The check engine light is on. Glow plugs, one week its one plug the next week its all plugs. starts fine at 10 degrees fahrenheit.
I ordered new vac hoses based on a thread with links and hose types. will check the actuator when i can get it in a garage, have been told about 3/4"of travel on this. Ive been seeing MAP sensor as culprit too, havent checked it yet but will get there.
The turbo seems to switch on and off when it chooses, sensor or limp mode?
Also the turbo whistle hasnt been around since the temp dropped below 35ish. relevant?

 

[danny miller]

I wonder if it could be the wastegate shaft sticking.

Ain't no wastegate here.

There's a VNT actuator, vacuum-actuated. You can put a Mity-Vac on the line and watch it move in and out.

But the N75 valve on the other side of that vac line is a common problem.

 

[jbruAT09]

The turbo is acting up again. after 3 weeks or so of the turbo working then not working it cleared out and ran strong for about a month. Two weeks ago the game started again. i took a road trip, when i left home the turbo ran. i stopped to fuel up and the turbo didn't boost, little upsetting to get passed on the highway by a chevy volt. ran about 3 hours, stopped for a snack, got back on the highway with boost. ran fine for a week. now here we are again, sometimes it feels like zero boost, other times it feel like i get a little kick, but still very noticeable that there is a lack of boost. accelerator to the floor and nothing. i have been reading around on the forum and there seem to be other common traits people describe but nothing exactly the same. i have found that 220k turbos tend to quit and need replacing, wondering if any of the other high mileage folks could chime in on that note. i have run without the MAF but no difference. been thinking about replacing the n75 valve first. i have yet to replace the hoses, im a little skeptical that its the hoses, it seems to me if the hoses were bad there constantly would be no boost. but i could be wrong here too. please help, no TDI should be passed by semis or chevy volts.