poor acceleration from cold-misfires and hesitates

Hello
I have had my P38 (2000 4.6 vogue) for a couple of months and I am really pleased with her although had to sort out a suspension problem (needed a new compressor).
In the last couple of day the RR really struggles when pulling away from cold - she hesitates, lacks any acceleration and produces a series of 'popping/misfire' noises from the engine. After about a minute she picks up and is no bother - runs smooth at all speeds. Did a couple of long runs over the last couple of days (2x 120 miles) - at one point after refueling I had problems starting the engine at the service station - it took a few goes to get started but again after a minute she was ok.
I changed the HT leads last week and the spark plugs were recently changed by the previous owner - they looked in good nick.
Any thoughts would be most welcome.......great forum by the way!
Thanks
Allan

i had same problem mate i found it was lumbar sensor, get it plugged in and it will tell you. hope this helps

leesp38v8 said:

i had same problem mate i found it was lumbar sensor, get it plugged in and it will tell you. hope this helps

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I hope that broke the back of the problem...

leesp38v8 said:

i had same problem mate i found it was lumbar sensor, get it plugged in and it will tell you. hope this helps

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lambda sensor?

dogsbody said:

lambda sensor?

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lol oh ya i just noticed that, my pc is pooooooooo

Continuing withthe 'back' problem I started her up today and rocking of the engine while turning the engine was quite un-nerving - the RR was all over the place and the misfiring was very worrying........nearly did my back in!!
Could you enlighten me me about this Lambda sensor ie what it does, where is it situated and is it an easy fix.

Parkheadlad said:

Continuing withthe 'back' problem I started her up today and rocking of the engine while turning the engine was quite un-nerving - the RR was all over the place and the misfiring was very worrying........nearly did my back in!!
Could you enlighten me me about this Lambda sensor ie what it does, where is it situated and is it an easy fix.

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The Lambda Sensor (you will no doubt have 2 - maybe 4 depending on year) Is located in the Exhaust system under the car....

These little devices measure the unburnt O2 levels in the exhaust and tells the engine management system to fuel the engine in a specific way to prevent over/under fueling and to reduce emmissions....

If these little devils are feeding back incorrect information to the Engine Management System, it will not be fuelling the engine correctly causing rough running and all sorts of other poor running issues....

Depending on year, there could be Lambdas both before and after the Catylictic Convertors to ensure correct Cat operation and fuelling....

Changing them is easy enough provided they unscrew from the exhaust without snapping off as they are usually fairly tight.

First thing is to get a diagnostic. But you could also be getting an air leak. Get some Engine Start, run the engine at idle and spray it wherever there is the possibility of an air leak, if the engine starts to rev you have found it. Favourite position on a Thor engine is where the engine idle control pipes join the plenum pipe which often breaks.

But do get a diagnostic.

Visited my local garage who did a diagnostic test - detected a fault with the air flow meter. He will replace the faulty meter with a new one on Monday - will tell you how I get on.

Replaced the air flow meter but still having problems - again when starting up and pulling away. It hesitates and threatens to cut out but then picks up at the last minute and then ok. The RR has a LPG convertion - it starts on petrol - could it be a fuel delivery problem?

Did u find the fault pal