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My Audi A5 1.8t has started having some hiccups after an engine job (Changed valves, timing chain & camshaft intake side)

The car starts fine, it sounds fine, but it has the following problems:

  1. If you drive the car at low load, does not matter what gear, the car seems to jerk a bit if you have the gas pedal in a consistent position. I can see the RPM gauge go some mm up and down and you feel the car jerking. It almost feels like misfiring. If you enter this loop of jerking, you either have to release the throttle or apply more load in order for it to stop. Once you do this, the engine feels normal again, until you go down to lower rpm an stay in a consistent manner.
  2. If the throttle is pressed down, you can feel there is a slight lag before you feel the engine "taking" and you feel a slight kick in the engine. This might be normal, but after the engine job, this "kick" feels a bit stronger.

If I try to do #1 on purpose to debug it, and I keep the engine in the loop/state of jerking over a period of +- 3-5 seconds, the check engine light flashes yellow, then I release the throttle, the engine light disappears.

It seems the engine is more prone to get in to this state if it is cold, then it stutters a lot.. You can hear the intake gasping for air and stops rapidly(bam bam bam bam), this is not so bad on a hot engine, but you still feel the inconsistency/jerking while driving on low load.

I did a ODB scan since my Vag-com is not available atm, It resulted in these three error codes:

  1. P0302 - Cylinder 2 misfire detected
  2. P000F(D9) - Fuel system over pressure relief valve activated
  3. P000F(D3) - Fuel system over pressure relief valve activated

These engine codes & the check engine light only appears if I hold the car in this jerking state over time (more than 3-5sec)

Does anyone have any guidance on what I could start troubleshooting? Thanks!

EDIT: I bought starter gas yesterday and tried to look for vacuum leaks. To my observations, there was no places the engine's idle changed. So I assume this might not be the case.

EDIT 2: I flipped coil #2 & coil #4 to see if the misfire moved to cylinder 4. I cleared the Codes & drove for a bit. The fail codes came again with no changes. So I guess the coil itself is not the case here.

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    Double check to ensure you don't have any vacuum leaks in the intake tract. This would mainly be from turbo to head. It is really easy to get a rubber lip folded over or bunched up on the bottom where you can't readily see it. Feel around all of the couplings to ensure they are in the right places. I don't know that it would exactly cause your issue, but it seems like a place to start. The over pressure relief valve activation has me wondering though. – Pᴀᴜʟsᴛᴇʀ2 Feb 18 at 14:08
  • Which model year Audi is this? – Zaid Feb 18 at 14:59
  • Have you contacted the person that did the work? – Moab Feb 18 at 15:10
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    @SølveTornøe I guess my question would be were there some symptoms that prompted the change of the valves, chain and cams? It seems to me that the work you did could cause code 1, but doesn't really seem like it would cause 2 or 3... so if there were pre-existing issues, those may account for 2/3... I'll do a little digging though. – kyle_engineer Feb 21 at 1:16
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    if possible try to get a reading of the fuel pressure to confirm that this is a real confirmed problem and not an error reading,and take a look at the connectors related to the fuel pressure controll and look for bad/reversed connectors. – trond hansen Feb 21 at 9:42

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