After looking on this forum and tried different methods, i am stuck with a fault code 16891 high revs. I recently replaced the manifold pressure sensor and ecu reset with the negative battery cable unplugged for 40-45 mins, reconnecting and idling the engine for a further 30 mins. I checked there were no fault codes, none where found. started the engine again, revs were normal but when i touched the accelerator and released, the revs were over 1000 and fluctuated. i turned the engine off and restarted, revs were normal. hope someone could enlighten me with this please.

Have a close look at the brake servo vacuum hose, I think you may find that it is leaking.

thanks for the quick reply On inspection the hoses look fine but the idle is now very rough, fluculating around 1000rpm. 16490 is the fault code now even though i replaced the manifold/barometric pressure sensorwith a new genuine origional part. im at a total loss. lol

Have you adapted the throttle body?

A barometric sensor fault can be logged not only if the sensor is faulty. If you have an implausible signal issue its out of the known range. This can be due to a throttle body that's not set or an air leak as already mentioned.

yes, ive done an ecu reset by disconnecting the negative battery terminal for 40/45 mins, cleaned the throttle body, also did the alignment of which you turn the ignition on but dont crank for 60 seconds then turn off for 10 sec and start the engine. i think i may have touched the butterfly in the throttlebody when cleaning though, moved it slightly.

Edited 13 February, 201610 yr by samhunter01

I'd want to do the alignment properly with diagnostic equipment and watch the adapted values to see its getting the full range.

Where are you located Sam?, someone looking at this might be near, and have VCDS available.

Edited 13 February, 201610 yr by Wino

Carrickfergus, Northern Ireland. Thanks for your replies, most appreciated.

checked it this morning and the engine management light came on. the engine was spluttering. the fault codes were 16687 misfire in cylinder 3 and the above 16490.

Sort the missfire on cylinder 3. Swap coil pack with cylinder 1 and plug with cylinder 2 and see where the misfiring moves too. You will get a barometric fault if it's got a missfire, it's not cause, it's effect.

Thanks again for all your help. I took the car to my local vag specialist garage. the coils and cylinders are all firing. the timing chain was also inspected, all good. the codes associated with the high rpm and map sensor were still there along with the lean fuel trim. the mechanic is confident that its the map wiring that could be the problem. im getting it checked on thursday by an auto electrician. the funny thing is, while I was on my way to the garage, the eml came on and I noticed the temperature guage was dropping halfway from the normal reading and back. I understand that this could also affect the rpm especially from a cold start and the rough running.

Have they flow checked the injectors?

HTP injectors have a nasty habit of flowing too much fuel. This causes missfire characteristics and rough running.

Compression test might be a useful thing to do also, especially if yours is the 6-valve 54bhp version.

I got the wiring checked today by the auto electrician. no fault was found with the wiring but he came across a hissing sound from the rear of the engine. it was the pipe leaking, he replaced it and cleared the fault codes. car is purring at normal revs. its amazing just what a piece of split hose can do to an engine. Thanks very much Tech1e and wino for all of your help and advice. All the best

Edited 18 February, 201610 yr by samhunter01

Very common fault which is why Wino asked back in post #2.

Glad it's sorted.