As warm running gets better, cold starting gets worse

[JonP01]

My Polo has only done around 1400 kms so far, but I am noticing that as the performance of the engine improves when warm, the cold starting - and to a lesser extent warm idle - are getting worse. When the car was brand new, the cold starting was actually smooth (ish), well certainly not rough or hesitant in any particular way. But after a couple of weeks, I noticed that the engine cold start was slightly rough as if there was a tiny misfire, but only until it reduced the idle speed down to normal (which I guess takes just under a minute or so) - at which point it was fine.

I never thought much about this since I felt this was par for the course and it wasn't really bad enough for me to make a mention of it at the 1500 km inspection last week. But over the last few days it seems to have gotten worse again and coincidentally or not, this coincided with me getting the car back after it's first inspection. Now the engine continues to run a bit rough at cold start as it did before but now as the idle speed drops to normal, it gets quite close to stalling. I have also noticed that the idle speed seems to be different after the first inspection - it seems to vary a bit more, generally being slower than before but faster than before when the air conditioning is on. And although the engine now runs noticeably better than ever before when warm, the warm idle is slightly more rough than it used to be - and again this seems to have happened after the first inspection.

It is possible (though I have not verified this yet), that the worsening of the cold start began after I put my first tank full of fuel in the car. I imagine it had BP 95 octane in it from the dealer and my first tank full was BP Ultimate 98 (as was the second tank full). Out of curiosity I am going to let the current tank get to almost empty, then put about $10 worth of Caltex Vortex 98, let it empty again and then try BP 95 octane, just to see if the different fuels make any difference to the cold running problem and slightly lumpy warm idle.

I guess what I am asking is whether this behaviour is normal for a Polo that is running in and improving in warm performance, or whether there is something wrong that needs to be looked at. I wasn't really worried about this until today when the car really hesitated quite noticeably as the idle dropped after the cold start. I am also wondering whether I just happen to have less than perfect fuel in the car, as the local BP stations dont get nearly as much traffic as the Caltex does and the BP service stations are quite old (unlike the two local Caltexes which are almost brand new).

I was also going to buy a bottle of injector cleaner and stick it in the tank as well, but I wonder if this would help given the warm performance is very good (definitely better than ever before), except for the very slight lumpiness at idle that it did not have before.

[Andy2285]

my golf gti is the same... gotta let the car warm up before the turbo can get to its full potential. just cruise along until the temp gauge gets to running temp see how it goes.

[MrDeathLad]

my golf gti is the same... gotta let the car warm up before the turbo can get to its full potential. just cruise along until the temp gauge gets to running temp see how it goes.

the problem with that is that the 77tsi has no temp gauge, just a warning light.

[gavs]

What kind of trips do you do in the car? Short or long?

[JonP01]

As was mentioned in the original post, I am not having any issues with performance whatsoever when the engine is warmed up except for when the accelrator is not depressed at idle - in which case there is now a tiny misfire that was not there when the car was new and many people might not even detect. But it is definitely there and definitely wasn't there before. Plus the cold start issues which have gotten worse as mentioned.

I am trying to ascertain whether this is due to a bad batch of fuel, something the dealer has done at the first inspection (since everything got worse later that day), the car "learning" the 98 octane fuel versus 95 (which from research appears to take two tankfuls), or some combination of the above...or something else entirely.

[JonP01]

What kind of trips do you do in the car? Short or long?

Hi Gavs,

I try to organise my car use so that I do not make trips shorter than 20 km. I live in a rural area and traffic is not usually stop-start and I will usually go through a 100 - 110 zone on each trip. Sometimes shorter trips are unavoidable but they are rare. For the most part the trips will be either 20 -30 km or longer ones (150 km plus).

Today I had to give my brother a lift home to the Blue Mountains so before leaving home, I filled the tank with a bottle of Nulon Fuel System Cleaner then topped up with Caltex Vortex 98 (about a third of a tank). I noticed that after about 50 kms the idle was improved and by the time I got back home (around a 160 km round trip), the idle was back to it's normal smoothness.

So although it is too early to tell, it looks like it might be fuel related. Possibly this is an example of not buying BP Ultimate if the service station is very old and they do not have a high turnover of 98 octane (as opposed to the Caltex which had new tanks and bowsers installed last year and gets a lot of traffic).

I'll be able to see over the next week whether today was just "lucky" or whether the Nulon really has cleaned something away. Then time to experiment with quarter fills from empty of Caltex 98 and Shell 98 (though the local Shells have old tanks and the Caltex as mentioned is almost new).

btw, I was really impressed with how the car went today. This was my first trip over the mountains with two fully grown men on board and full tanks. Despite having an engine the size of a tennis ball and a turbo the size of a pea, the thing effortlessly climbed the mountains in 5th gear with only very light throttle required even in the steepest parts. My brother was knocking the car (in jest) before the mountains because it was only a 1.2 litre, but when he saw it effortlessly going up those steep hills in 5th - still with bags of grunt to spare he was very impressed. I used to drive VN Commodores and EA Falcons for work in the 90s and neither were as impressive as this little car is.