Engine Performance problem
2003 Renault Megane 4 cyl Two Wheel Drive Manual 73000 miles
----------------------------------------------------------------
Hi, I do the same drive to and from work every day, 15 miles fast country roads at 50 to 60 mph, 17 miles motorway at 60 tp 70 mph, 15 miles cross country at 30 - 40 mph 47 miles in total each way 94 miles per day. Traffic conditions always very similar daily average speed 39mph for whole journey. My megane 1.9 DCI diesel does approx 39mpg if air temp below 0 degrees C, 42 mpg at 0 to 6 degrees, 45 at 6 to 10 degrees, 48mpg at 10 to 14 degrees, 50 mpg at 14 to 20 degrees and 56 mpg at 23 degrees and above. the above MPGs are pretty reproducible at any given air temperature and I get same result if I warm car before resetting computer and have tried holding hose to make sure it stays cold and gets hot suddenly to be sure it is not the thermostats. I think it is an air temp sensor sending duff information to the engine management computer and am told it could be sensor between air filter and turbo - Any ideas and suggestions on how to fix would be greatly appreciated. Thanks Regards David

Hi davidjosey,

The sensor between the air intake and turbo unit is the Intake Air Temperature and is the most like culprit if it is with regards to the ambient temperature.

You need to check the Engine Coolant Temperature sensor too, it might not be sending the correct engine heat signal to the ECM.

You mentioned resetting the ECM, do you do it often? The ECM should not be reset if nothing is wrong as it needs a relearning time and would be back to square one if resetting is done frequently.

Hi, thanks for your reply. Sorry my description was not clear, have never reset Engine Management Computer, what I meant was trip and fuel consumption computer. I fi Let car warm up for a few miles then re-zero everything I get pretty much the same fuel consumption. For my normal drive to work I can look at the air temperature when I get in the car and know within 0.5mpg what fuel consumption I'll do on the trip. Do these sensors need replacing or is it just a case of cleaning them ?
regards, David

Hi David,

If the check engine light is not showing, then some cleaning might help but DO NOT scrub them. Just use carb cleaner to spray and clean off any oil or dirt that might have accumulated.

Start with the air intake hose sensor first.