Chat Increase in revs when starting from warm

A

Alcamo

Member
Hi All,

2004 75 tdi, BHC, 162k Stealth map

Car is a daily driver, does most of our donkey work, both short and long runs. I noticed that initially when starting from warm the car would rev as if my foot or the carpet had caught on accelerator. This has become more regular (from warm) and I think that the car idle is now slightly higher. I haven't noticed an increase in fuel usage. The car returns 60 - 62 mpg despite many very short, in traffic journeys. Any ideas?
 
My guess would be that the injectors are needing a service - there is a dribble of diesel left over when it is switched off causing the revving at the next re-start. My AMF car used to do that - every 10 or so starts it would rev as if I was at a traffic-light grandprix - then return to normal. Got the injectors serviced/restored by Darwen Diesels and that problem was completely eliminated - additionally the idle was subsequently much smoother.
 
Hi Robin, thanks. The rise in revs is only momentarily. It settles back to 'normal' idle very quickly. With limited knowledge of diesels I did think it suggested over fueling and residual fuel makes sense. I wondered if an extra dose of diesel is injected if a temperature sensor has failed and it thinks the engine is cold? I guess I need to get a diagnostic scan to see what is showing.
 
My unrequested revving was literally for a couple of seconds after turning the key and it firing - what you're describing sounds exactly the same.

If I'm not mistaken there isn't a diagnostic for this on the 1.4tdi - it will just keep doing it every few starts until you resolve the worn injector issue. Once my injectors were refurbed the fuel efficiency was also markedly better (around 10-15%) and no more faint smoke visible when giving it full throttle.

VCDS or similar will tell you if a thermostat or temp sensor needs to be fixed (I've done a few!) - easy and quick way to make a 1.4tdi run better.
 
Alcamo said:
Hi All,

2004 75 tdi, BHC, 162k Stealth map

Car is a daily driver, does most of our donkey work, both short and long runs. I noticed that initially when starting from warm the car would rev as if my foot or the carpet had caught on accelerator. This has become more regular (from warm) and I think that the car idle is now slightly higher. I haven't noticed an increase in fuel usage. The car returns 60 - 62 mpg despite many very short, in traffic journeys. Any ideas?
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It might be worth getting a VCDS check on the temperature sender. Remember that the temperature gauge in the dash may well be ok but there is s separate feed to the ECU. So it may be thinking that the engine is colder than it really is.
VCDS can show both readings, or just replace the sensor with a new one if you can’t check its output.

Just s thought?
Steve B
 
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