Not Smooth, Jerky, Misses

**11mallard** · 2nd April 2012, 20:57

Hi All, I would appreciate some input into a problem with my Veccy. Its a 1.8 of 2003 vintage. 77,000 on the clock and regularly serviced. Over the past year have replaced the EGR, Front Cat together with O2 Sensor and Cam Sensor. Serviced 2 months ago with new air filter, GM part synthetic oil and filter, I tend to do the oil at least once a year if not sooner, left the plugs as they were only 6 months old, Bosch Super 4's. Recently getting the usual P0420 Catalyst System Efficiency Below Threshold (Bank 1) Clear the code and O.K., for a week and its back. She is holding back when puling away from rest and as if missing a couple of beats then picks up, mainly when cold.
Also had a code saying rich mixture? Otherwise engine is really smmoth and quiet.
Wonder if its Maf Sensor??
Sorry its abit long but would really appreciate your help.
Thanks in advance, Nigel.

**Highwayman64** · 23rd March 2013, 19:46

Looks like no replies to this thread unfortunately but to save me re-typing, I have almost EXACTLY the same symptoms.

Recurring P0420, Lambda sensors replaced, Coil Pack replaced, Garage advising 'probably' a Cat but I am wary and not convinced, would a failing Cat cause the loss of power, mainly in colder temperatures and under higher loads (i.e. uphill)

**paz_badboy4life** · 24th March 2013, 02:08

with your car running disconnect the MAF sensor. if the engine note changes then all good, but if not then its an indication that it might be ****ed. try swapping it for another one from a Veccy which is same as yours then you can take it from there. you can get cheap ones off eBay but i decided to spend a bit more and buy original Bosch one. use a bit of carb cleaner and clean your EGR valve out. mine had an electrical fault on it so although it was nice n clean it was malfunctioning. a second hand part rectified the issue. good luck.

**cont1204** · 24th March 2013, 13:07

Sounds like a MAF sensor. Had an Omega that did this. I can't remember if unplugging the MAF on a 1.8 puts it in limp home mode or not but it's worth a try. Just unplug it and go for a drive. Your revs will be limited if it's in limp home mode but if not, see how it goes. If it does go into limp home mode just plug it back in and you'll be fine.

**Critch** · 24th March 2013, 13:15

Go to garage ask then to give an emissions print out at idle an 2000rpm

ask them to take reading of the MAF

Don't replace with anything other than genuine or OE Bosch one.

as cheap aftermarket sensors can cause more problems.