Anyone know how to fix an unstable idle at startup?
Engine: 2.2 TDCi 200bhp

Symptoms: start the car from cold or having been left for a bit and it runs stutteringly until you rev it a bit and then something seems to click in and it's then smooth and stable and runs fine thereafter, as if it was only running on 3 cylinders to start with and then the 4th kicks in. If you don't rev it first and just put it in gear and try to pull away gently it will stall. It does it every time I start the car but there are no persistent DTCs.

History: It has done this ever since I got the car in 2015 when it was 3 years old and done 70k with a full Ford service history so it has not recently appeared or got worse. Since then I have changed the MAF sensor and fuel filter (several times).

What could it be? Glow-plugs? Engine map? Something else?

Hi,

I've driven a few diesels with weak or missing glowplugs and never had this issue.

It sounds more like a weak injector...but that wouldn't have lasted 10 years with no change. In this case the only option I can come up with is a bit of poor mapping.

You could ask Ford whether there's a PCM update available for your car. But if you've put up with it for 10 years then I don't see much point in trying to fix it now.

I'd monitor live data, things like fuel rail pressure etc etc and look for something that changes to try to see what "clicks in" (as this is the big clue - if you can find something)?
Disconnect each injector in turn to compare with your "normal" start?
Is it temperature related i.e. does it get worse as the temperature drops which glow plug issues obviously do?
Otherwise, as said it is a difficult one when it has existed for years with no change.

Good shout, thanks. I tried to really pay attention to it on Sunday morning when it did it and I'm thinking I agree it's not an issue with the glow plugs either. It does feel like an engine mapping issue as it's like on the old petrol cars with the manual choke where the engine would die if you didn't have the choke out and you pulled it out just in time and the engine came back from the brink.

It's doesn't do it if the car is warm, so again, feels like more evidence stacking up in favour of the engine mapping for cold start.

I'm dubious about this "engine mapping" thing?

Are you saying Ford have it wrong or it has been re-mapped since new by someone or ?

What about simple things like a sanity check on the various temperature and other sensors (ambient, intake, fuel, coolant or whatever) as you mention it's like Ye Olde Worlde choke setting, hinting at temperature air or fuel related issue?

13 hours ago, Shearers said:

I'm dubious about this "engine mapping" thing?

Are you saying Ford have it wrong?

Yes. Ford mapping has always been poor quality in my experience, it's not unusual for them to release PCM updates over the first few years after release. They also never seem to have the finesse of German mapping, for example. The EGR mapping on 16v 1.6 TDCI was poor. The DPF regen mapping on 8v 1.6 TDCI was poor.

Manufacturers also add some 'cheats' into the mapping to pass emissions testing, such as restricting RPM when stationary, and leaning out the fuel mapping at 'extra urban' cruising speed, which can leave a strange dead spot either side of that speed/RPM. Interestingly, I've found my own car (non-Ford) doesn't charge the battery after a cold start until the throttle is pressed. I don't know whether that's intentional to reduce emissions when testing or just a bit of an oversight. I also had an older VW with the 'emissions fix' which had a single misfire on every journey after about 5 minutes. That obviously wasn't intentional, just a bit of missing code somewhere while switching between temperature maps I suspect.

Very interesting. I had an Audi 3.0Tdi that was transformed by a Bluefin remap. As standard it was nice but the throttle response was underwhelming. After the remap it was superb; responsive throttle and masses more torque. I am certain the factory mapping was to keep the CO2 emissions down (although it was still annoyingly 17g/km over the tax boundary!).

I confess I don't know what I would be looking for on the sensors like ambient, intake, fuel & coolant during startup to know if they are the cause. I see no issues with how the car runs normally so how could I tell if something was out of whack during the warm up on Forscan?

Throttle response is purposely damped on standard maps for driveability as well as emissions and reliability. Electronic throttles are so sensitive that even the smallest movement from a slightly shaky foot or over a rough road surface could see the RPMs going up and down making for an uncomfortable and potentially unsafe drive. There are also torque limiters in lower gears to reduce wear on the clutch, DMF and gearbox for more powerful turbo engines. Aftermarket remaps are the only way to get rid of things like that. Manufacturers should be able to make 'smooth' maps though.

That sounds complex, the mapping thingy.

What I mean is things like checking that temperature sensors don't read stupid values e.g. when ambient is 10 degrees, other temperatures are not silly.

Diagnose Dan had a case where multiple very expensive parts were changed on an S-MAX to fix a misfire when the fuel temperature sensor was faulty and reading far too high.

It is simple live data sanity checks on things like that and demanded and actual parameters are similar at all times?

Just following the thread - have had the same issue since I bought mine in July. If it stalls after start up (if I don't rev it when it judders) it won't roll when in drive (automatic) the next time....

This sounds like the same thing I have. It's like the cold engine fuel management part of the map doesn't work. Does yours do it every time you start up or just when cold? I noticed it more recently with the cold and very wet mornings. Car is absolutely fine after you've revved it a couple of times.

So mine was doing this on start up (even would cut out sometimes after idling for a few seconds). Accompanied by a few other issues (engine malfunction when accelerating hard). Turbo had gone and DPF was clogged - had both rectified (aswell as EGR delete) and it's fine since.