Wintry weather set to cause mayhem to drivers (of MK2 Polos!)
Polo MK2 warm air feed / temperature regulator
It was all going too well. Despite the inevitable stress of preparing to move out of our old home and into a new one it definitely felt like we had got this. Due to the process of 'completing' on the sale and purchase of property having to happen in a single day, an early rise and flurry of activity ended with us ready to head off to the new abode around mid day.
I loaded up the Polo with a few last minute things and set off down the road making good time. Unfortunately about 20 minutes into the journey things took a turn for the worse, helpfully just after I joined a dual carriageway. The little VW which usually pulls surprisingly well for a tiny car was struggling to reach an acceptable speed. A recent similar experience with an intermittent loss of power was enough to indicate that this was not simply the car struggling with the extra weight it was carrying that day.
I drove on cautiously at lower speed and things settled down for a few more miles, but alas eventually the car started to lurch and progressively slow down despite applying full throttle. With my hazard lights on I made it to a small refuge area, on the approach to a roundabout, before the car died completely. It wouldn't start again. Admitting defeat and in a somewhat vulnerable spot I called for recovery.
Annoyingly enough, the car started straight away after help arrived. The sun came out, thawing me out from the chill in the air. I drove to our new home without failure with the reassurance of the recovery truck following behind. It could have been worse: We moved home, everything else went smoothly and being exhausted myself, the Polo was abandoned on the driveway for a week before I had the time or energy to think about fixing the problem.
When I did finally get my 'petrol head' back on I went through all the obvious causes in my mind. I faintly remember the battery light came on before the car died, but I was more concerned with safely making it to a refuge area so I couldn't be sure. The alternator probably is quite old and there is a bit of noise from a bearing or pulley in that area. But the symptoms didn't quite fit.
All the ignition components were renewed fairly recently, though it's always worth checking them. I resolved to do some investigation and thought a minor service couldn't hurt even if it wasn't quite due....
But it wasn't until some serious cold weather arrived a few days later, bringing snow, rain and hail all in one day, that I realised in my post-move exhaustion I had forgotten one obvious variable that had changed lately which could be related to the problem: the ambient temperature.
I had been told in the past by more experienced Polo owners that the cars are very susceptible to icing of the carburettors in the winter. For some reason I never considered that as a potential cause of running issues. But the symptoms fit so well: the more my speed increased the more the car seemed to struggle, presumably the increased air flow created even colder temperatures inside the carb, forming more and more ice until the engine was starved of air completely.
I decided it might be worth checking or replacing the warm air feed. There are several parts to the system:
a corrugated pipe from the exhaust manifold cover (already replaced on my car)
a temperature regulation 'sensor' inside the air filter housing [p/n 030 129 828]
a control box that sits between the intake pipe and the air filter [p/n 052 129 608 D]
The temperature regulator [red part shown above] and control flap box [at the top of the photo with vacuum tube connected] are both fairly cheap and easily available as OEM parts in so I ordered them in.
I decided to pull a spark plug before I replaced these parts for more clues. I had a problem with fouled spark plugs from too rich air/fuel mixture before. This was mostly caused by an incorrect carburettor setup, but perhaps the occasional icing of the carburettor was also a contributing factor.
On pulling a spark plug I found it was in good condition. But the problem had only just arisen so probably was unlikely to have caused serious fouling of the plugs yet and at least it confirmed I had the mixture just about right.
I removed the old sensor from the air filter housing and unclipped the old control flap box, replacing them with the new parts, making sure to reconnect the two vacuum pipes. All in all it was less than an hours work.
Firing the car up I could confirm correct functioning of the flap by removing the first section of the air intake (simply held on by a single screw). Using my phone as a camera I took pictures of the inside of the control flap unit at rest and once the car was started.
In an ambient temperature less than 20 degrees celsius, the flap should be partially or fully open, allowing warm air into the carburettor.
It was 10 degrees the day I started the car, the flap was nearly fully open, and I felt a sense of achievement (despite my unscientific approach of not testing the old parts beforehand). I did at least confirm there was some vacuum coming from the pipe that controls the flap using my trusty vacuum gauge which is fast becoming my favourite tool.
So the warm temperature feed is definitely working now... All that remains is to take it for a drive and see if it's fixed the problem. But did I mention the weather has been awful lately? Maybe I'll wait till it warms up a bit...
… Hang on!