Hi guys. I searched and researched but was unable to find anyone with similar issue, so I'm reaching out for help.

The car is 6-speed with SRI, catback, NWP spacers, VIAS block-off plate, brand new spark plugs, brand new rear coils (I just replaced three) and brand new valve covers.

This has started a while ago and was getting worse with time. Once you go WOT in 2nd gear (from 2k to 3k RPM) the car shakes very violently, like the engine is about to jump out. The shaking is also present in 3rd gear, but it's not that bad. After 3K RPM (or if you don't go WOT), it accelerates just fine. Idle is very smooth but somewhat low (I think) - 600 PRM.

I have installed NWP spacers, valve covers, new plugs and coils about a week ago and it did make a difference, the shaking decreased a little, but is still very bad.

I know that P0455 and P1448 might be caused by the EVAP system (either the gas cap or the valve/canister combination), but will the EVAP issue be causing that much engine vibration? P0300 just came on today.

I was thinking it might have something to do with engine mounts or suspension (I'm on coilovers for 2.5 years), but the codes don't make sense then. Also, if I go WOT in 1st gear, there is no vibration whatsoever, so I'm thinking suspension/mounts are not the issue.

I don't think it's the MAF, because the idle is very smooth. I do feel a little loss of power, but that might be a placebo effect.

Would you guys recommend changing the front coils, even-though they throw no codes?
Do you think that EVAP codes might be the cause of P0300 coming up?

This is so strange. I think if it would have something to do with an air-flow, my idle would be pretty bad, but it's very smooth.

Any suggestions on what to check, if any of you experienced similar issues?
Thanks in advance guys!

 

You'll have to log what the maf is reading and compare to normal running cars.

Methinks maf still.

Just shooting in the dark, I have not experienced this problem before.

 

Thanks for the reply. Will definitely try replacing maf as I have one laying around anyways, will see if that changes anything.

Meanwhile, today I got P0300 freeze frame (+ P0300 pending from yesterday), so 4 codes in total. Maybe something else will pop up that I will help me narrow down the issue.

I also noticed a strange rattling noise at low rpm (in neutral or in gear, doesn't matter, around 1200-1500 PRM), kinda sounds like a heatshield rattle (very subtle), yet it sounds like it's coming from a timing chain housing at the very top (close to where the VIAS is). No rattle on startup or idle, just when the RPMs go down to around 1500 RPM.

Would an issue with a tensioner or chain cause the vibration as I describe it?

Also, after I put some gas in today and start the car - it died. So, I will definitely have to fix the EVAP issue (car starts normally if I don't open the gas cap), but I don't think it will get rid of the vibration, which is the priority for me right now.

Any more ideas guys?

 

Anyone? I just noticed that when it's more humid outside, the vibration is a little less noticeable. So weird..