Erratic throttle response when cold

[HPsauce]

I also posted my latest symptoms over on AudiSRS as a fair few of them have similar engines. The first suggestion was the plugs giving up as it's due for a service.
With Audi long-life servicing up to now (80K about due when I'll do the cam belt, water pump etc. as well) how old could they be and could it be that simple?

[Adrian E]

May have only had 1 set of plugs in its life - think they're due at 40k? Defo worth changing but I wouldn't expect your symptoms to come and go if the plugs were the sole cause

[HPsauce]

Yes, it seemed like a long shot to be honest. Why would a significant proportion of 8 plugs start to misbehave at the same time?

Thinking about it maybe being excess fuel (for whatever reason) I tried a slightly different starting procedure just now; normally I turn the ignition on, open the mirrors and set the SatNav before starting the engine, so the fuel system gets pressurized:

Put the key in the ignition and immediately started it, keeping the starter motor going until I was confident it was running. No throttle.
It started badly but quickly though was still "chugging" somewhat around 500rpm after at most 3 or 4 seconds of starter motor when I released the key. But it quickly settled down nearer 1000rpm without me touching the throttle.
It was still a bit "rumbly" so I revved it for a few more seconds and it was then idling smoothly.

[HPsauce]

I'm just wondering how much of a factor fuel could be, presumably in conjunction with something else?
My last 2 fill-ups have been (I think) Esso 97 followed by BP 97. Neither of which I have ever used before in this car.

Today, getting a bit low and needing to go out I called in at my "local" and filled up with cooking 95 (Esso). Only took 55 litres as I got the "tilted down filler" side of a very busy (bloody Tesco local shop and people "park" at the pump! ) forecourt so will be a bit of a mixture. Did about 10 miles so the fuel lines should be well flushed through.

The "theory" is that lower octane is easier to ignite, I'll see how it goes over the next few days.
When I got home it was nicely warmed up and starting fine, as ever when hot.

[Kalchev]

80k miles with a single fuel filter? Wow you really got clean fuels
Get a good quality fuel filter and change it asap - it's cheap compared to all you have done and the change is real easy. If it's not the filter, it's value added for the operation of your audi. 80k miles with one filter... wow. Not sure what kind of marketing the audi long-life servicing is. I change filters every 10-15k km, including the petrol filter, disregarding the fact I'm on LPG. I use only VW spec or better filters, you just can't compromise with these, they are consumable anyway.

[HPsauce]

No difference with 95 RON.
Fuel filter will be replaced when it's serviced in about 10 days time.

But..... FINALLY I have a sort of error code:
16500 - Engine Coolant Temp. Sensor (G62): Implausible Signal
P0116 - 35-10 - - - Intermittent

Could that cause these problems?

The sensor is about 9 months old, so I'm trying to get a warranty replacement as it was supposedly guaranteed for 2 years.

[HPsauce]

This morning I put the old sensor back (yes I kept it!) and it started fine and felt suitably brisk and urgent on the road.
Been for a bit of a run and it started OK again when I got home; will try again in an hour or so.

The problem with the old sensor is that the temperature display on the dash was always low, but the unit has 4 pins, so is there a separate sensor in it for ECU use?

Might toddle off to ECP on Monday and get a proper new one. Though fitting them is a bit of a pig.
Every step is easy and quick, EXCEPT fitting the locking clip back in, which with my big hands took longer than the whole of the rest of the job combined, and then some!
It's easy to lose as well, so "TIP" I tied a long bit of thin string around it so it didn't disappear down behind the engine.

[HPsauce]

Originally Posted by HPsauce

The problem with the old sensor is that the temperature display on the dash was always low

But it's now also throwing a solid error code that comes back immediately on clearing:
1 Fault Found: 16502 - Engine Coolant Temp. Sensor (G62): Signal too High P0118 - 35-00 - - Readiness: 0110 1101

So I'll get that replaced ASAP. Anyone know the significance of the Readiness code, it was 0000 0000 yesterday but the engine was running today while scanning?

As for the sensor I took out, only a few months old, but giving this:

Originally Posted by HPsauce

16500 - Engine Coolant Temp. Sensor (G62): Implausible Signal

The thing actually rattles if you shake it! Obviously something has broken inside.

[nakata]

If not have other error at ECU. Erathic throtel response is from fuel injector. I have the same problem, with the change of them is normalize it. First sympthoms is at cold engine and going worst at the time. Is good to change and presure regulator which is responsibile for not starting at first time at cold engine.

[HPsauce]

I'm going to see how it behaves with a proper coolant sensor first.

Checking back on my VCDS scans it had an intermittent problem with that sensor from before I bought the car.
That problem got worse and I replaced it with what turned out to be a cheap piece of eBay rubbish that failed badly relatively quickly.

Today I bought a proper OEM part (£40 vs £7.50 on eBay) and will fit it later.