Doctor Diesel

Megane mysteries….

Web01Hello Doctor
I have a 2005 Renault Megane 1.9 dCi, which has been a pretty reliable car. I am saying that so that you may appreciate, being a Yorkshire lad, that I don’t want to spend loads of dosh on keeping the old thing going.
For a while now, during both winter and summer, a fault has emerged. When I press the gas to pull away, or when I ease off the gas, (what’s all this gas Trevor?) and then press the gas pedal again, it does not respond, it does not accelerate; but when I lift off the gas pedal, and then press it again, it accelerates as normal. When I first noticed this, it was intermittent, and it happened once a month, or once every three months. More recently it is occurring more often, once a week, then maybe miss a couple of weeks, then happen twice a week.
My second question about the same car is, when it is summer and warm and dry, the engine runs pretty smoothly, however when the weather becomes cooler and feels more moist (autumn and winter), the engine does not run as smoothly. It just seems to generally run more unevenly, and when summer returns, it starts to run smoothly again. With it being so intermittent, my local garage hasn’t found the fault. Have you any ideas?
Trevor Beadle

I am pretty sure that the first problem will turn out to be a sticking throttle body, which is a butterfly flow control device, a bit like in a carburettor (remember those?), that is used to control airflow in some diesels, mostly at lower engine speeds. It’s effectively located inside the inlet manifold assembly and it’s rather fiddly to get to – it may need a long reach socket spanner, and you might have to unplug some electrical connections. So it’s probably best left to a garage that knows the problem and knows how to clean the throttle body – although it’s only about a 20 minute job, so it shouldn’t cost very much. Don’t let anyone persuade you that you need a new throttle body (£200 to £300) as it’s usually just some cleaning with some solvent and a bit of lubrication that’s needed. It sounds like your local garage doesn’t really know the Renault engine, so try and find a small garage that knows Renaults better.
Regarding the uneven running in the cooler seasons, that’s a bit more of a challenge Trevor, and I think maybe only a (costly!) diagnostic check may eliminate, or identify, some of the possibilities. But here are a few suggestions:
– EGR system is clogged up – clears in warm weather, comes back when cool again. – The fuel filter needs changing – thicker diesel in winter can’t get through the filter
– Dual-mass flywheel on the way out. It sounds and feels like the engine is running roughly, but it’s actually roughness in the transmission line.

Let me know how you go on. It might be the right time to sell the car, when it is running well Trevor, if you can get the throttle body sorted, and you never know if the other roughness might disappear when that is done! Let me know how you go on.
Doc Diesel

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