Renault Espace (1985 - 1997) - 94 2.0 Engine loses power for a second or two

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Mon 8 Jun 2009 00:30
94 2.0 Engine loses power for a second or two - mhi
Starts fine, runs happily on long journeys, but on local trips it's plagued by frequent (every minute or so) loss of power for a second or two. This shows as uneven idle speed, too, fine when cold and (probably) fine after running for half an hour, but otherwise fluctuating 500- 850 rpm (should be steady 850). It's just had a new distributor, spark plugs and plug leads as part of a horribly expensive breakdown repair.

How do I track down what's wrong? My guesses are ignition (I'll get it a new coil lead soon, since the original is old and stiff and 15 years old), fuel supply or engine management electronics. Is it practical for a DIY owner to get anything useful out of the "diagnostic" connector in the engine bay, for example, and will it do any good for this sort of thing?

There are no strange noises or other symptoms with the loss of power, and it doesn't seem to be getting any worse or better. Doesn't depend on the weather (within the range of May & June). I don't think it can be a faulty idle air valve, despite the uneven idling speed, since the effect happens under power as well. (It's rather off-putting to drive, not knowing whether 0-40 mph will take 10 seconds or 14 seconds.) This model uses Renault's "J7R" engine.

Edited by Dynamic Dave on 08/06/2009 at 01:17

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Sun 12 Jul 2009 00:42
94 2.0 Engine loses power for a second or two - mhi
The cause eventually diagnosed as a faulty lambda sensor. Most of the time it worked, but now and again it gave fluctuating readings -- not quite badly enough to show up as a fault in any diagnostic test. Fixed by a very helpful and thorough garage who ended up taking the car for a drive with a fancy engine test thing operated by a passenger. Fixed at last (new sensor).

Apparently the moral is to replace the lambda sensor every ten years, whether it appears to have failed or not.
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