UK-POLOS.NET - THE VW Polo Forum

Hi guys,

My 96 Polo (1.6) began having idling problems a few months ago. Specifically, the revs would drop by a few hundred rpm momentarily every 60 seconds or so. I read here that cleaning of the throttle body was the cure for this, so I cleaned it. The idling is now perfectly smooth and consistent... except when the air conditioning is turned on.

Prior to cleaning the throttle body, the aircon made no difference to the idling behaviour. But now, turning it on causes an initial drop in revs, as extra load is placed on the engine, but then the revs quickly recover and oscillate around 1500 rpm increasing and decreasing by a few hundred rpm on a 1-2 second cycle. Turning the aircon off immediately restores the idling to normal. While driving at any speed up to 50 mph (or more) with the aircon on, lifting off the accelerator causes the car to lurch suddenly as if a parachute has just been let out the back of it, and the engine struggles. Again, switching the aircon off immediately restores the engine behaviour to normal. The aircon itself puts out the usual amount of cool air while all this is going on.

Any ideas what is going on here?

This problem has been fixed by replacing the fuel filter. Not that I think the filter was the cause but it was due for replacement and I followed the procedure in the Haynes manual. This involves depressurising the fuel system by removing the fuse for the fuel pump and cranking the engine until pressure is gone. According to the wiring diagram, a couple of engine sensors are on the same circuit as the fuel pump and would also be disabled...
Anyway with new filter in place I put the fuse back, started the engine and checked for leaks - none. So then I thought I might look at the idle issue. I switched the aircon on and instead of revving like crazy as it usually did, the engine just wavered between 1,000 and 1,100RPM. After a week of driving with aircon on the problem completely disappeared and all is still normal a fortnight later.

Nice one

Another Australian member then?

A/C must be vital over there