Megane idle problem

Haakon

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If you can think of it, ive changed and swapped with a few expections.

I think im going back to basics - it still feels like a vacuum leak. Now I know its not the upper plastic manifold or any of the sensors and connections on it as thats been swapped from the Scenic thats runs well.

So that leaves the lower alloy manifold to head gasket. This was never removed so i didnt doubt it - but its the only place left air can be getting in after the injectors and o rings were all checked and replaced.

Its a bit of a pig to get out as the top engine mount bracket bolts to it in one place. I am ordering a new engine mount anyway as the cheapie i tried is crap so am replacing it with a good Lemforder brand one - ill do it all one go then.

I've never heard of the pressed steel gaskets failing... Maybe it got corrosion from when the engine was sitting on the concrete outside for a few months. It was wrapped in plastic and kept dry and inlet was taped up, but ill find out when i get it off.
 

jo proffi

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how does the ecu controll idle airflow?
assuming it has an idle control valve, can it be bypassed and replaced with something mechanical ?
 

Haakon

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how does the ecu controll idle airflow?
assuming it has an idle control valve, can it be bypassed and replaced with something mechanical ?
Drive by wire throttle body - no ICV.
 

Haakon

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what happens when it is disabled?

That was a good thought! Isolate the ecu and let it run just mechanically. Alas the unplugged default butterfly position has it running at 2000rpm.... And the butterfly cant be moved manually.

It occurred to me the lifting hooks are bolted to each of the head, and had the whole engine and transmission weight on them. Enough flex in the head casting to crack a seal on the steel manifold gasket...?

Stay tuned for a few weeks when i have the mount ;)
 

Haakon

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Never did sort this. Have another car with the same engine that idled perfectly and swapped everything. Still no joy.

I ever swapped in another ECU and it still did it.

Im totally out of ideas. I think the Valeo flywheel is the problem and somehow is upsetting the ECU but no idea how or why. I got it registered and drove it around for a while hoping it would settle, but now the only solution (beyond the Jerry can and match…) is to get another whole car of the same model and trans and transplant the whole drivetrain. It’s a bloody hassle.

Im into it $4K and countless days of work and im about to walk away from it.

For sale - lots and lots of new parts for a Megane 2…
 

Haakon

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If anyone knows of an amazing mechanic or tuner in Canberra that really knows their way around a scan tool I’m all ears.

It’s runs ok cold on open loop but something is making the ECU disregard the upstream o2 sensor when it goes cloesd. Reads like a slow sensor but it’s not. Which makes it look like we are back to a vacuum leak, but fucked if I can find one. Swapped over whole inlet assembly, done all gaskets multiple times etc. PCV system all good etc.

It has to be electrical and/or ECU.
 

JoBo

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Stab in the dark, feedback/ faulty alternator?
 

dmccurtayne

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Have you done a reset of the auto adaptives some of those ecus chuck a bitch fit after different parts are changed you would need to do this with a clip or other good scan tool I always have safe Delphi ready to download for people on here
 

Haakon

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Have you done a reset of the auto adaptives some of those ecus chuck a bitch fit after different parts are changed you would need to do this with a clip or other good scan tool I always have safe Delphi ready to download for people on here

Yep, hours on the CLIP. Adaptives reset, flywheel target programming procedure done many times, throttle body stop learning done.

Even went to update the ECU software but it was up to date.

STFT is low so its like its running rich, but its lean as buggery looking at the pinging and spark plug condition.
 

Haakon

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I know some cars (inc Megane) whinge sometimes with aftermarket single mass flywheels throwing fault codes, but they still run ok. And if by some chance i managed to fit it one bolt hole out (7 bolt flywheel with one bolt out a bit so it only goes on one way) it just wouldnt start at all.

This one is a proper dual mass, its just a Valeo branded one instead of the factory LUK. I cant think how an air gap issue with the crank angle sensor would effect this - it would either start or not...
 
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dmccurtayne

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I know some cars (inc Megane) whinge sometimes with aftermarket single mass flywheels throwing fault codes, but they still run ok. And if by some chance i managed to fit it one bolt hole out (7 bolt flywheel with one bolt out a bit so it only goes on one way) it just wouldnt start at all.

This one is a proper dual mass, its just a Valeo branded one instead of the factory LUK. I cant think how an air gap issue with the crank angle sensor would effect this - it would either start or not...
Agree unless it's got a low waveform would need to scope that and have a good known to be sure but that would be on the I doubt it pile.
 

Haakon

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Anyway, I booked it in at the Canberra froggy car specialist for a second opinion... Desperate times - first time in 30 years of mucking around on cars I've done that!!!!

Thats not for a couple of weeks, might pull the wiring loom out, strip the conduit and go over it with a fine tooth comb. Maybe there is something with resistance thats creating a dud signal somewhere...
 

Haakon

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Got back to this recently. Spent a whole day swapping another front end wiring loom - hoping I had a dud or corroded connector somewhere… Nope. Sigh.

Came back to the crank angle sensor again. Had a brainwave and used some blutak on the end of the sensor to measure the air gap and compared it to the scenic (it was more for sure) but probably right on the high side of the 0.5 - 1.8mm spec. I was able to shave down the sensor a little so it sat more in by half a mm and lo and behold the bloody thing ran perfectly. Rev hang gone, pinging gone, idled like a champ for a well over 5 minutes!!

Then it started hunting again and went back to its old ways, although perhaps not hunting as much and at lower revs.

So. That did something. I don’t know what or what it means, but something changed. Reset the adaptives and redid the flywheel target programing procedure but that lovely steady idle was merely there long enough to get my hopes up…

Downstream o2 sensor is reading rich at 0.8 volts and I think the short term trim is pulling fuel which explains the pinging. Those two seem to be contradictory which is hurting my brain….
 
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