After Giving A Quick Hard Boost While Driving, To 4000 Rpm Engine Shud

[robtek]

Hey guys..

Started a couple weeks ago, If I put my foot down in any gear and boost it, I.e. from the lights in first gear to 4000rpm, then back off or change to second and keep going, either way soon as I back off, the engine shudders and revs fluctuate quite a bit, the engine almost stalls

> I've cleaned out throttle body

> air intakes

> plugs are still good

> always run 98

> let the engine warm up before pushing it

> my mechanic gave the car a look over after changing the rear diff bush and said car looks good

Any ideas?

Anyone have experienced similar issues?

Cheers

[Paulie2256]

Prob valve springs

[robtek]

Thanks for the quick reply man... I was really hoping it wasn't valve springs.. anything else it could be or are the symptoms a trademark for worked out or over sprung valve springs?

[freeze_dk]

Valve springs

[Mr_4.0]

Is the car stock?

If not, what mods?

Anything changed?

[robtek]

13psi tune from the X3 flash unit

Monza cooler

K&N filter

APS Phase 1 (the ecu only I think)

T5 with worn out clutch lol

Flutter BOV

130000kms on clock, very clean engine and no smoke etc

All the mods were done by previous owner

shouldn't the stock valve springs still be ok? what's their max rwKW? or is my beast pumping out too many rwKW?

[Paulie2256]

Valve springs are like shock absorbers, they wear out after a while and go soft.

Still only assuming it's the valve springs though.

[Mr_4.0]

What model car?

[robtek]

2003 BA XR6T

[Mr_4.0]

At 13 psi your valves will be floating like crazy with ba stock springs.