mk4 gti anniversary problems

[topher]

is the misfiring/shuddering on cold start-ups only lasting around 30 seconds?

[danyo]

yea that's right! have you had the same problem?

[topher]

nah my cars never go wrong

it would suggest something is going wrong with the secondary air injection system (pump on the front of the engine that blows air behind the valves to help burn off the additional cold start fuel and warm the cat up). The common fault is a leaky pump because the rivets that hold it together break up and fall out.. however with your other symptoms it is quite possible there is an issue with the solenoid (N112) that activates the pump or the vacuum lines to the solenoid.

[danyo]

when you say leaky pump....what would leak out exactly? oil? water?

[topher]

air but dont get too fixated on the pump itself the vac lines that control the solenoid that switches the pump on are in the bundle of mess under the inlet manifold and if they're plumbed in incorrectly or leaking you effectively have a boost leak which can cause your lack of power and poor fuel economy.

oh and just to add, the fault code that comes up relating to the thermostat (error in mapped cooling system?) can also be caused by a knackered coolant temperature sensor, which can also lead to power/economy issues.

[danyo]

so the chances are the bits i have already changed, something out of them could be faulty!

[KeithyGTI]

I.....

[danyo]

Hi Mate,

i believe it was a faulty thermostat that was fitted. car runs a lot better now and has cleared the engine code. although it does run a little rough on startup...