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Discussion Starter #1
My Laguna has developed a problem where after a short drive the car beings to slow down and chuck as if im not not pressing on the throttle and changing down gears doesnt help either. Once I pull into the side and leave the engine idle it sounds/acts fine but not until I stop the engine and restart after a few moments does it stop happening.... Its not giving any warning lights or logging any problems on the computer and my mechanic is lost??? need help please...
 

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I would investigate the TDC sensor first because a) it rarely needs replacing, just cleaning and b) if there were any problem with ignition (e.g. coils/leads/plugs), after a period of time the ECU tends to baulk and flag an emissions warning light.

However, any mechanic worth their salt would have checked all of the above first and foremost, I should think. Especially on a modern Renault petrol engine (although coil degradation is certainly not a Renault specific issue.)
 

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Discussion Starter #4
No they checked the coils and seemed happy it wasnt them. They thought it might be a problem with the electric throttle switch(rather than a cable sytem) that was failing but were unsure if this was to blame....
 

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I think they mean the accelerator pedal position sensor - it's a potentiometer the top of the throttle pedal and used by the ECU to establish (along with its internal parameters and senses) how far to open the physical throttle - as bmpecc says, there's no cable, it's all electronic.

If you can get the car hooked up to diagnostics, it should be possible to see on the live data read outs (Clip has handy graphs for this) if the reading off the pot is inconsistent at certain positions or generally erratic. On my car, there's a percentage readout for the amount of time during which the ECU could not estabilish a position from the pedal although I'm not sure how reliable it is. My old car said 14% - I'm pretty damn sure I'd notice if the car was not responding to my throttle input 14% of the time (although I suppose it could smooth out 'spikes' in the travel.) Either way, it's certainly worth cleaning the connections on it to see if it improves the situation.
 

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Discussion Starter #7
dont know where this part is located or what its called but logically id guess its near the fuel injectors...
 

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You should have a go at taking it out, spray some electrical contact cleaner into it, then move it through it's full range a few times and leave to dry (it evaporates fast - and works wonders for the pots on old stereo volume controls too ;))

I'm assuming there's one in the throttle body itself as well to tell the ECU how far open the physical throttle plate is, but I've not heard of that one being a problem, nor any cases where chaning the whole throttle body turned out to be a long-term solution to similar issues.
 

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Discussion Starter #11
So after xmass I got the ECU reprogrammed and all has been well so far but the car seems to be very slow.
60mph is about as high as she will go and the speedo seems a bit off at lower gears. Is this a sign of a bad job done on her, or is the 1.6 engine just not strong enough for the weight of the car as people keep saying to me?
 
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