I hope somebody can help me with an ongoing problem with my car which has started intermittently losing power. It is a RENAULT MEGANE SCENIC 1.9 DCI Feb-2003- 52 PLATE and done 115,000 MILES.

The initial problem occurred about 4 months ago as I was going up a hill on the motorway. When I changed down from 5th to 4th to gain more speed whilst overtaking a lorry I had been stuck behind, the car lost all power , but didn’t stall and I immediately pulled over to the hard shoulder. The engine management light had come on but then went off and the car was still ticking over. Having checked everything looked okay under the bonnet and sounded normal, I re-joined the motorway and drove the remaining 90 miles without further problems. The next time it occurred was 4 months later on a hot day as I pulled away from a roundabout onto a dual carriageway. All power was lost as I accelerated up from 3rd to 4th gear. As soon as I took my foot off the accelerator the power came back. However, half a mile down the road as I accelerated a little more to overtake a vehicle, I again temporarily lost power. It recovered again and I drove the car to the garage without further incident. It has been there ever since as my ex-Renault mechanic hasn’t been able to find the cause. All the different parts mentioned below have been changed or checked.

Now each time the car is first driven from cold it will cut out at 3500rpm, but once heated up, it will not rev past 2500 rpm without the revs dropping completely. Also recently, my mechanic found that the car having had the sun on the bonnet for a morning, he could then get in to start the car and find that immediately it would only rev to 2200/2500revs before cutting out to tick over speed.

The car had a major service at 113,000 and timing and auxiliary belts changed at 104,000. The turbo whistles but has been doing this since August 2011 but otherwise functions normally.

The car has had a CLIP diagnostic test which revealed incoherence between cam and crankshaft sensors. Both these have been checked and changed without effect.

The EGR valve was checked and found to be clear and working ok

MAF meter was replaced with no effect.

Timing belt has again been checked and found to be correct.

Finally, a replacement ECU unit has been fitted – but this also has made no difference.

My ex-Renault mechanic and all his contacts have run out of ideas. Has anyone any thoughts or possible suggestions please? I am desperate!

Look forward to receiving any help and advice. Many thanks.