- Engine bucking MK4 AVH
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    1. Junior Member idrivea2002golf's Avatar
      Join Date
      Sep 18th, 2003
      Orange County
      '02 VW Golf GLS
      03-20-2017 08:52 PM #1
      Hi All,

      Iím having an issue with my MK4 2.0 AVH, with the 02J 5-Speed. This is a long running issue and as such I have a lot of things to share. Please bear with me as this goes back about 6 or so years.

      2010-2011 (dates are starting to get fuzzy):
      I noticed my engine has a bucking feeling while at idle. I canít feel the hesitation at all when you put 200 Ī extra RPM. I didnít really do much because it was my daily driver, it wasnít affecting milage and no damage was being done (iíll support this later with some evidence).

      I have a job not requiring I drive every day/provided a company vehicle. I had some time to tear into the engine and see if I could figure out whatís going on. I started with simple things:

      Spark plugs: new NGK plugs per VW spec (i donít recall the specific number but itís in my Bentley)
      new spark wires
      new coil (it threw 4 misfire codes and the coil was the cause), note this is the single coil with 4 leads not the coil packs on each cylinder
      New temp sensor (100K service)
      new timing belt (100K service)
      new water pump (100K service)
      New timing belt and accessory belt tensioner (100K service)
      new accessory belt (100K service)
      Performed a smoke test looking for a vacuum leak: none
      Performed a fuel system test (canít recall numbers but did meet the Bentley requirements)
      Replaced fuel filter (this has been done a few times since this started, i change it about every 20K)

      At some point near November 2013 I was on a long road trip, sitting in traffic and I noticed the water temp climbing. I pulled over and found the fans werenít running. Turned out the fuse on top of the battery blew and took the fans and AC with it. As I figured I probably warped the head and since I was having the bucking problem I took the opportunity to have the head machined.

      I bought new intake and exhaust valves, seals, etc. for the rebuild and sent it off to a shop. I should note (iíll see if i can find the picture) when I pulled the head 1 of the cylinders was an odd white compared to the rest. I found it interesting but didnít think much of it, this is on Cylinder 2 (important later).

      While the head is off I perform an oil leak test on the rings. I put all 4 cylinders at the same height in the block and poured oil into the pistons. I left it for a period of about 48 hours and no visible amount of oil disappeared. Our farm mechanic and I thought the rings were OK (he does diesels, VWs arenít his forte).

      Head comes back from the machinist. Looks pretty, new valves, etc. At this point (i know someone is going to mention this) I put a TT Tuning cam in. Very mild, i think it is the 260. The guys at TT said it was just one step up from the OEM cam. I donít fault this because the shake had been occurring for 4 years prior to the cam.

      With the install of the rebuilt head I took the time to replace some other components:

      new OEM rate fuel injectors
      new 4 bar FPR (i know it doesnít help much on the 2.0s)
      New seals, gaskets, etc for everything I removed and even some I replaced to CYA
      Removed and cleaned the MAF
      Removed and cleaned the throttle body (yes i did have it re-adapted)
      New air filter
      new plugs/wires again (this was 30K after the previous change, i was in there, theyíre cheap)

      Some parts iíve replaced for other reasons which may be important:
      Iíve replaced the fuel pump because the sender was messing my the gauge (not during the head install, but worth mentioning)
      145-amp alternator, the 90-amp died and they were the same price

      Engine mods:
      Neuspeed pulley kit
      TT Tuning cam
      GIAC tune for the cam (i truly hoped this would put the fuel maps right for the cam, nope)
      Thatís it

      Just today I replaced the motor mounts. I suspected maybe the bucking was just the mounts giving the engine too much room to vibrate. Didnít help.

      I have performed a few tests:

      compression gave me 190, 180, 185, 190. Well within spec, I noted Cylinder 2 seemed lower than the rest and it made me think about the color of the residue on the head when I pulled it. I donít know if it means anything.

      Fuel is at spec still.

      Vacuum is about 16.5, I canít help but think this is low. It doesnít bounce at idle. If you tap the throttle is responds correctly (again, i donít recall the response I just remember looking at the description of how it should, and it did)

      I do need to perform an O2 reading for STFT and throttle position. I will do so in the next few days. Hopefully the rain tomorrow washes away the salt. Iím not driving the car much now as I have a winter beater for the snow.

      I donít know if itíll mean much but this is a California car, has been all its life. I just recently moved to Illinois (North of Chicago), about 6 months ago. As soon as the temperature dropped I garaged the VW and itís been sitting in the heated garage all winter so far.

      I feel like iím missing some of the diagnostics iíve done. If i remember anything Iíll post it up.

      Any help is greatly appreciated. Iíve been neglecting my poor car and now itís time to get it running correctly.

      Odometer reads 145K, iíve owned it since new in 2002.

    2. Junior Member
      Join Date
      Jun 25th, 2015
      Clovis, CA
      1999.5 VW Jetta GLS 2.0L; 1999.5 VW Jetta GLX 2.8L 12V
      03-22-2017 12:32 PM #2
      I would recommend taking a good look at the MAF. You stated that you cleaned it, but there was an issue with the stock MAF that came equipped with the cars. Some MAF failed and others slowly failed causing incorrect readings to the ECM, thus incorrect signals to all other important components. If you MAF does not have a yellow dot next to the part number, then it is the original MAF. With the amount of mileage, you should replace the MAF anyways.

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