Thirst & Sluggish GTI T150 MK4 Driving Me Mad!!!!

**GazGTITurbo** · 19-09-2007,11:11 PM

My GTI T150 is drinking petrol and is slow and sluggish and I'm all out of ideas! I've had it in the garage and they said it was the air temp sensor so that was £80. Only, thats made sod all difference. If I'm driving like a saint at 65 mph the average mpg is showing 33/34, then the minute I use the turbo and pick up speed it drops rapidly!

I'm gonna take it back to the place I got the air temp sensor and tell them to run the diagnostics again (for free) and see if theres anything else but if anyone has any ideas I'd be very grateful.

Sorry - also - when should my turbo be kicking in??? It seems to kick in at about 1500 rpm in 2nd and 3rd? I've got a Bailey Dump Valve so you can tell when the turbo is being used cos it blows off - is this right? and could the dump valve be my problem?

Thanks

Gaz

**Eshrules** · 20-09-2007,12:24 PM

Originally Posted by GazGTITurbo

My GTI T150 is drinking petrol and is slow and sluggish and I'm all out of ideas! I've had it in the garage and they said it was the air temp sensor so that was £80. Only, thats made sod all difference. If I'm driving like a saint at 65 mph the average mpg is showing 33/34, then the minute I use the turbo and pick up speed it drops rapidly!

I'm gonna take it back to the place I got the air temp sensor and tell them to run the diagnostics again (for free) and see if theres anything else but if anyone has any ideas I'd be very grateful.

Sorry - also - when should my turbo be kicking in??? It seems to kick in at about 1500 rpm in 2nd and 3rd? I've got a Bailey Dump Valve so you can tell when the turbo is being used cos it blows off - is this right? and could the dump valve be my problem?

Thanks

Gaz

i take it the engine you speak of here is the 1.8T? i'm not very clued up on the petrols im afriad, but from what you describe, its pretty normal fuel usage, to average around 30/35 on a m.way run is ok, not mind blowing.

what do you average around town? it should be around 20/25 mpg, dependant on traffic conditions etc.

also, i think you've got the DV concept the wrong way around..... the DV blows off when you let off the gas, ie when the turbo ISNT being used, the excess boost pressure is released from the system, which is what gives the hiss noise.

if the DV is hissing when you're giving it some gas, there could be a fault with the DV.

**Crasher** · 20-09-2007,02:14 PM

A common reason for this when cruising at steady speed is the engine coolant thermostat being jammed open so the over cools and hence over fuels the engine. A fault code read would show this as a lambda error. Is the engine check light illuminated?

**GazGTITurbo** · 20-09-2007,11:20 PM

Hey, thanks to both of you for your replies. No, I've had no engine management light on, and I've had the car fully diagnosed today and the lambda sensor is fine, as is everything else and they have told me they can't find any fault - yet its still doing it? They did suggest that if the Dump Valve (which was professionally fitted by Demon Tweeks) might be stuck open and causing a lack of pressure??? What do you reckon?

**aBoijj** · 20-09-2007,11:42 PM

I've seen various instances of weak springs on Bailey dump valves on other cars. Try taking the dump valve out and running a standard setup for a week or so and see if that makes any difference.

Originally Posted by GazGTITurbo

Hey, thanks to both of you for your replies. No, I've had no engine management light on, and I've had the car fully diagnosed today and the lambda sensor is fine, as is everything else and they have told me they can't find any fault - yet its still doing it? They did suggest that if the Dump Valve (which was professionally fitted by Demon Tweeks) might be stuck open and causing a lack of pressure??? What do you reckon?

**Crasher** · 21-09-2007,12:02 AM

I didn't know you had an aftermarket dump valve. I have had so much trouble with all sorts of makes of valves that I now will not sell and refuse to fit anything other than the factory (admittedly slightly unreliable) original unit. It is what I have on my own car.

**GazGTITurbo** · 21-09-2007,11:21 AM

Right - I didn't know that about the DV - forgive me cos I'm not great at this, but if this was faulty, would this cause the sluggishness and crap fuel consumption? Also - I don't know whether this is connected or something different for me to worry about but when you start it up - sometimes it fluctates up and down revs between 1000 and 1300 which sounds really rough and then after about 30 secs - it'll settle at 900rpm? could this be connected?

If you think I should get shot please say so - including the Dump Valve and the temp sensor I've already spanked £300 on this and its not even sorted yet!

**Crasher** · 21-09-2007,01:37 PM

It could also be the AMM as these don't show up as a fault code very often. Don’t jump ship after spending only £300, people often spend ten times that chasing a fault. Perhaps you should take it to a different garage. The pulsating idle is often down to a dirty throttle body.

**GazGTITurbo** · 21-09-2007,02:37 PM

Thanks - I've booked it in with a local German car specialist garage but he can't fit me in until late next week so I'll just have to limit my driving to neccessary journeys and be nice to the girl at my local BP garage!

Whats the AMM?