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    Thread: Vacuum pump diagnosis

    1. 09-09-2010 09:39 AM #1
      My car (02 Jetta 1.8t AWP) has been suffering from cold start and normal idle issues. I figured it was a simple vacuum leak issue, so I've been tracing vacuum lines for a while.

      To rule out coils, I got them all replaced under warranty and even did the overlay harness.

      The car has been to the dealer a few times and they have given the diagnosis of the vacuum pump. They said at one time they replaced a 20 amp fuse, the other time they simply said the vacuum pump needed to be replaced.

      Yesterday I decided to check out the vacuum pump. I located it under the car and the line from it runs from the electric pump to the brake booster. It didn't, however, ever turn on. I never felt the pump kick in and my idle was terrible.

      I'll probably continue looking at the lines, especially the one from the brake booster to said pump. Any input?

    2. Member
      Join Date
      Apr 11th, 2010
      Gainesville, FL
      09-09-2010 04:18 PM #2
      Bumping this up for you.
      I'm confused about what vacuum pump you are talking about. The brake booster hose connects to the intake manifold and the small non-electrical suction jet pump underneath the IM.
      Is the pump you are talking about the SAI pump, down beneath the throttle body - close to the oil filter? It has 2 black corrugated hoses - one from the air filter box and the return to the combi valve.

    3. 09-09-2010 10:11 PM #3
      Hmm. The dealer told us and showed us a diagram of this vacuum pump. The one that connects to the brake booster that is located underneath the car behind the firewall. They said it was a $300 part and it had blown a fuse before. I found out the hose that connects to the brake booster from said pump was cracked where it connects. I cut off the cracked portion and reconnected it. Also had to replace the battery, since it finally quit on me. So far the issue hasn't come back. I'll see how long this lasts.

    4. 09-16-2010 12:51 AM #4
      The issue is back. It's not very consistent-one day itll do it, the next maybe not. This is the part the dealer said was faulty: http://www.ecstuning.com/Volkswagen-...181C/ES308137/

      The dealer claims there is an internal short in the pump and the hoses are cracked. Would this cause the rough idle? Any other ideas?

      Also, when my car hits 4k rpm, my engine has this shaky feeling too it, but it's only right around 4k. Anything under or over feels great. What could be causing this?

      Thank you guys for any help, as I'm a dub newb. I'll be buying a VAGCOM cable this weekend.

    5. 09-27-2010 10:10 PM #5
      Got an update; I replaced the MAF sensor with a brand new genuine VW MAF. Still a terrible idle, but not all the time. I still get a random ASR light as well and my shifting goes nuts. I chose to replace the MAF sensor, because my idle was doing terribly, I unplugged the MAF and suddenly it cleared out and idled fine, even though it triggered the ASR in its absence.
      I noticed that the ASR light pops up after around 40min to an hour of driving, but shutting the car off and restarting will remove the light and issues.
      The idle issue is only at low RPM, however, the car has even bogged down and died at turns.
      I just ordered the infamous VAG COM scanner. Any ideas while I wait for the scanner in the mail?

    6. Member elRey's Avatar
      Join Date
      May 15th, 2001
      16vt 2.0L MK4 Jetta Wagon | B6 A4 Avant
      09-28-2010 10:53 AM #6
      I'm guessing you have an automatic transmission. Manual cars do not have a brake booster vacuum pump.

      I would look to see if you could by-pass the pump. The brake booster should still have a line directly to the intake manifold. Leave that connected and just disconnect and cap off the line leading to the vacuum pump. Also electrically disconnect the pump.

      See is that helps your idle and cold start issues. If it doesn't, the pump is not your problem.

      And if you don't notice a difference in your brake pedal feel or braking performance, leave the pump disconnected.

    7. 09-28-2010 09:08 PM #7
      Yes, you are correct on the transmission. 5 speed automatic Tiptronic. I'll definitely try the suggestion tomorrow and see if that helps. I appreciate the response.

    8. 10-08-2010 11:26 PM #8
      I bypassed the vacuum line for the vacuum pump. So far so good. It has been starting without misfires. My MIL light went off as soon as I cranked it up. I haven't got a good cold start yet though, so I'll see how it fares in the morning. The light came back on, but there is a vast improvement. I'll check it all out in the morning. Thanks guys.

    9. 10-09-2010 11:47 AM #9
      Misfires never went away. Still missing at idle, primarily on cold starts. Just got a new code: P0420 for Catalyst efficiency below threshold. Where to go from here?

    10. 10-09-2010 06:07 PM #10
      Upon looking further, my PCV hose is split fairly good around the base. How would this affect the idle?

      I swapped my cylinder 1 & 2 coils with cylinders 3 & 4 to see if my codes change. Will post results.

    11. Member
      Join Date
      Apr 11th, 2010
      Gainesville, FL
      10-09-2010 09:42 PM #11
      This will affect your idle even cause misfires. Get a replacement set of PCV and breather hoses from Eurojet or 034Motorsports. I like the 034 Motorsports set.

    12. 10-13-2010 01:12 AM #12
      Got it coach. Swapping coils didn't provide anything conclusive. After resetting the computer by unhooking the battery, as well as siliconing up the crack on the pcv for a temporary fix, it ran fantastic like it never had before for 2 days, but then returned to the bad idle.

      Codes that came back:
      P0300 Random/multiple cylinder misfire
      P0301 Cylinder 1 misfire
      P0303 Cylinder 3 misfire
      P0411 Secondary Air Injection Incorrect Flow Detected
      P1780 Neutral Switch Fault detected

      Going to order the PCV piece. Any other ideas come to mind? The SAI pump doesn't make much noise on idle so I don't think thats causing a code. Will check those hoses again. Swapping the coils didn't provide conclusive data. Not sure about that P1780 code..

    13. Member sounrealx's Avatar
      Join Date
      Apr 3rd, 2007
      Brandon, Florida
      01 AWD Turbo Jetta
      10-13-2010 08:30 AM #13
      When you say "vacuum pump", they could mean either the "sucktion jet pump" or the SAI. If your sai isn't turning on, you may have a sticky thermostat, or a bad n112 valve. leaking jet pump hoses and things that attach to the intake mani will cause a bad idle and misfires

      Jet suction pump under the intake mani:

    14. Member hootyburra's Avatar
      Join Date
      Feb 19th, 2007
      Bloomsburg PA
      337.sold 2.slow
      10-13-2010 11:00 AM #14
      if you need an sai pump I have mine for sale.

      g/l with solving your problem.
      CTS 3076 kit, CTS 750hp FMIC, CM FX400, 2L, AEB, RMR IM, Raxles, Eurodyne, 870's...

      Vag Scans, pm me

    15. 10-14-2010 12:37 AM #15
      I can hear the SAI pump on startup, so I believe it is fine. The vacuum pump I was referring to is part of the braking system and ties into the brake booster. The dealership diagnosed my problem as such and quoted me for it, but I wasn't too sure about it. I know for sure my PCV hose is shot, so I will have to isnpect that stuff much further.

    16. 10-14-2010 04:36 PM #16
      My ASR light is going nuts now. I got it three times in an hour of driving. Car would jerk like crazy into a shift. Only have the P1780 code to work off of in regards to transmission. My MAF sensor was just replaced, so I dont think that is the cause. What do?

    17. 10-16-2010 12:00 AM #17
      Shameless self bump

    18. 10-19-2010 02:25 AM #18
      Quote Originally Posted by T-rey View Post
      My ASR light is going nuts now. I got it three times in an hour of driving. Car would jerk like crazy into a shift. Only have the P1780 code to work off of in regards to transmission. My MAF sensor was just replaced, so I dont think that is the cause. What do?
      I think I'm having the same issue with my 03 Jetta 1.8T Tiptronic. My ASR light has been coming on at random times over the last few months, and when it does it has a serious effect on the shifting. Whenever it happens, the tranny shifts very, very hard. If I shut off the engine and restart the problem usually went away.

      The problem surfaced again about four days ago, and now almost every day since. When it happens the car also has almost zero acceleration. Like I put the pedal to the floor and nothing happens. Tonight it happened, and now the check engine light has come on and is staying on. I'm going to try to get it to a VAGCOM in the next few days, but am afraid that won't give me any concrete leads.

      Have you made any progress with yours? Any more info to share?

    19. 10-19-2010 08:38 PM #19
      Hmm I posted on 4chan's /o/ automotive board, and an audi tech said the PCV is likely the culprit. Apparently the PCV hose leaking cuases misfires which cause bad MAF and O2 sensor readings, which in turn will make it think the MAF is nuts and throw the ASR light and cause the symptoms. I ordered the PCV hose from ECS and will be installing when it arrives. It has to be sensor related because when I clear the computer by pulling the battery cables, it runs amazing for about 70 miles or so when the computer gets all of the sensor readings stored. Hopefully this fixes it, if not I'll be buying a vagcom.

    20. 10-24-2010 02:49 PM #20
      Got the part, but my L hose is cracked at the base and stuck in the cylinder head. Looks like I'll be pulling the intake manifold next weekend and replacing all those hoses.

    21. Member
      Join Date
      Apr 11th, 2010
      Gainesville, FL
      10-24-2010 03:47 PM #21
      Shoulda got the 034Motorsports kit - replaces the stupid, plastic - L shaped hose into an integrated silicon section.

    22. 04-23-2011 02:13 PM #22
      I managed to pull the cracked piece out with a dent puller. I replaced the piece with a new part from the dealer. Patched up the rest with vacuum line, cleaned out the PCV which was completely clogged and made sure it was working again, and cleaned the throttlebody and now I'm running misfire free.

      I'm sorry I never posted my fix for the longest time.

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