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New member here; something of a virgin at this Forum malarky.
Well done gents for all your dilligent attempts at finding the solution. I am experiencing an identical problem with my recently acquired 2004 Scenic II 1.6 and I have to say I am a member of the 'put up with it' team, especially as my wife drives it the most!
However, I am intrigued as to what the solution may be.
A search on Google did throw up a comment on NEW CAR NET, the UK new car guide - latest news, roadtest reports, features, driving tips, advice, car Insurance, car comparisons, car loans, buying guide that suggested the 1.4 and 1.6 engines run over lean when cold, to keep them in line with emissions criteria. All your sensor testing and replacing won't change that, and only adjusting the programming of the ECU would make a difference. Then the theory is it won't pass the emissions test...and how do you adjust the ECU programming...?

Jon
 

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Hi Jon - if all the sensors are OK and the ECU is at the manufacturers settings the ECU will adjust the fuel setting depending whether the engine is warm or cold. The ECU monitors not only engine coolant temperature but also that of the inducted air.:)
If any of the sensors or their connections are faulty the ECU will not get the correct information
 

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Thanks madnoel. You're right of course, and one assumes that the manufacturer sets the ECU up such that it runs smoothly in all conditions. Another point that makes my comment even more incorrect is that emissions tests are only valid when the engine is up to temperature, I've learned today. ECU check report has to be the first stop, I guess...
 

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Hi All,

Got the same problem on my Megane Coupe. I've changed every sensor I can find on it (and there are lots). The only one I haven't had a crack at yet is the camshaft position sensor, which I've just got the Renault workshop instructions on, so will have a go at that shortly.

The purpose of this post is to ask if the original poster ever managed to resolve his problem? I notice he did mention that he was going to have a go at the camshaft sensor himself, and am wondering if he ever got round to it and with what result.

Cheers,

Pete

P.S. Oh for the days of a normally aspirated engine with no ECUs, sensors, etc., etc.
 

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Hello folks,

I am also experiencing similar problems with my 52 plate 1.4 16v Clio.

Problem:
When cold i.e. after being left over night, car generally starts ok but until it is up to temperature, it miss fires or 'chugs'. Definetely down on power as well. When the car is up to temperature it goes absolutely fine.

Attempts at fixing:
So far the Arnold Clark garage i bought it from have changed the engine coils, air filter, spark pulgs and Water Temperature Sensor.

So far none have made any difference to the car and it is going back into the garage on Tuesday for them to look at it again.

Thank god i got the Arnold Clark autocare warranty as the coils would have cost me over £300 and would have made no difference. All the other stuff has cost me about £80 but i'm not keen on spending anything else unless I know it will either be covered by the autocare or it will 100% fix the problem.

It's a real shame because it's a really decent wee motor, but now i'm thinking of just gettin shot of it and buying anything other than a Renault.

Also, some little ¤¤¤¤ has stamped on the bonnet of the car and made a nice big dent which has cracked the paintwork!

Anyone know someone who is good with car bodywork in the Edinburgh area?

Will keep you all updated on how i get on with the garage but i'm not to optimistic
 

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Discussion Starter · #27 ·
Since I first posted about this problem I have done a lot of experimenting in my car.

To sum up my findings:

-I have tried replacing every sensor on the engine apart from the 2 oxygen sensors (thankfully I didn't pay for the testing, I borrowed a sensor and returned it after a couple of days to my garage) - NO DIFFERENCE.

-I have tried all brands of fuel and also tried using fuel additives - NO DIFFERENCE.

-New spark plugs, air filter etc. - NO DIFFERENCE

-Cleaning the throttle body - Ok, this one's very, very weird. Other owners have noticed this too. Apparently the throttle body can accumulate dirt very, very easily over a very short period of time.

I clean mine every 2-3 months. The difference is obvious when driving around and also, the all-familiar engine hesitation when cold disappears for 1-2 days after cleaning the throttle body. After that, it reappears. No idea why that happens.

I also tried a new throttle body, no difference whatsoever.


So I've come to this conclusion:

-its either one of the oxygen sensors
-or the ECU software (a bug)
-or a problem with the exhaust

I will report back my findings concerning these areas ;)
 

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I've had a very similar issue with a 2.0 16v scenic for the past two years. I suspect its the knock sensor at fault causing the timing to retard and lack power. A new sensor is about 120 quid so I've been shopping for a used one. Finally found one for a tener and will fit at the weekend. I'll let you know how it goes
 

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Has anyone tried replacing or cleaning the EGR valve to solve the problem? (assuming the 1.6 has an EGR) If cleaning the throttle body works as a temporary cure, it might be worth cleaning the EGR and all the pipes it connects to.

I've had EGR issues with my last 3 cars (Vectra, Alfa 156 and Laguna) and in all cases, the cleaning solved flat spots and hesitation. I did the goona the day I baught her and she ran as smooth as new until recently.

But..... 6 months down the line I'm having similar hesitation problems and am going to clean the EGR valve again today. I'll post my results and if its caked in gunk, post a few pics to highlight the problem.
 

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Intrigued with this problem, what about trying another coolant sensor from a previous version of the engine and seeing what the difference is. Strikes me without some sort of ecu remap the ecu wont enrich the mixture enough when the engine is cold, substituting another coolant sensor with different resistances across the temperature range could at least point you in the right dirction.
 

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The MAT sensor didn't make a difference either...

I'm running out of things to replace! :-(

Could it be a faulty oxygen sensor? I've done a couple of emmissions test and they came out perfect...

Also as I said there are no fault codes stored in the ECU...

The last few days its gotten really, really cold here (around 0 degrees)... Problem is more pronounced, i.e.:

I start the car, starts up fine, revs fine, rock steady idle, I unpark, set off with 1st and 2nd up to 3000 rpm, all is well, 20 meters later I reach an intersection and stop to look, as I take off in 1st again I feel a power drop at about 2000-2500 rpm, like someone's taken my foot off the throttle... This was very noticeable, passengers asked me what was wrong... For the next 5-6 minutes, until the engine temp gauge reaches 1/4 of it's travel I felt 2-3 almost unnoticeable flat spots (power losses) under 3000 rpm...

Tommorow I will be replacing the camshaft position sensor... Could it be dirty? Is it affected by the temperature? Could this be a throttle valve problem? Why does the car run perfectly when hot but has these problems when cold? I'm going insane!!!!

Has no one else run into these symptoms before? Even with other models?
Did you find the problem? I have same symptoms on my Megane 3
 
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