Hello to you all. I am hoping one of you may be able to help me with an issue which has been plaguing my poor car. It is a Mk1 VRs with the AUQ 1.8t engine on 170,000 miles.

 

Until recently the car performed like a champ. I had it converted to LPG and it ran like Usain Bolt on both petrol and LPG. Recently it started to show signs of hesitation, a lumpy throttle if you will. I changed the NGK OE plugs with some Bosch Super 4s, did an oil change and flushed the rad, although it enjoyed brief respite the ****ty running returned.

 

Eventually, the engine coughed out a pending code of P1176, which refers to the O2 sensor. I cleared this fault accidentally on Torque Pro and my car instantly ran more badly than ever, to the point where LPG ran like a kangaroo so I switched to a diet of petrol. I replaced the O2 sensor which did sweet FA. Further rummaging around Google suggested the PCV valve may be out, I replaced the pancake valve connecting the breather to the inlet to no avail.

 

My car is currently warming up very fast from cold but not overheating. The idle is very uneven and the sound is difficult to describe, it just sounds 'off' in some way. I cannot say whether the performance is affected because my paranoia is making me drive like a 90 year old lady.

 

The error code has not returned and Torque Pro does not report any pending codes or any evidence of knock. Unplugging the MAF did nothing other than illuminate the dash light which disappeared when plugging it back in. My breather valve appeared oily, not dripping wet but it was there. Oil appears the correct colour and so does the coolant. Oil filler cap oily not milky.

 

Does anyone have any clues?

OK where to start?

firstly Bosch Super 4s are cr4p - especially on LPG (despite what your LPG converter might tell you)

the only plugs you should use with LPG are the NGK BKR7e (colder plug with solid coper core) and if you are running with a remap then you gap them a bit tighter

AT 170K  there are a million little things that might need replacing in the VAC and Boost lines of which there are plenty.  the big Y-pipe being the  most obvious and everything else that touches the inlet manifold including PCV/one way valves/and the weird little "suction jet pump" as its called

 

rough idle raising and falling is classic VAC leak so test by spraying a little bit of carb cleaner in and around the vac lines, if the engine note rises then you sprayed a VAC leak, fix that bit of pipe and then try again.

Ideally if your not mechanically minded get a garage to Smoke test the boost and vac lines for you - if you are then there are videos on youtube to build your own testers

if you fit a boost/vac gauge its a great help in identifying issues

 

if you look through my history there are lots of boost and vac related issues that I had when I have my 1.8T 4x4

just to add the bottom end of the PCV system has a big one way valve that gets caked in cr4p, I stripped and cleaned mine but at a lot less than 170K

These engines love good quality petrol,

ie: Shell V Power or equivalent, not saying it will cure your problems but cant hurt.

When was the throttle body last cleaned?