My polo as started having problems with acceleration...I'll go into 3rd, then the speed goes down to what feels like 30mph but the revs stay, the only way I can get it going is either going into a lower gear or taking my foot off and back on to the accelerator. Even when going into a lower gear after a few seconds it will do it, there will be about a minute or two of driving where it won't happen and then it will kick back in. I've had this happen a while back and it only lasted a few days then the car was driving normally, we put it down to the clutch. As time has gone on and it's kicked back in it feels like it is getting worse, even when trying to pull off in 1st gear it pulls back and slugs along and then starts juddering as if it's about to stall so I have to whack it in 2nd to drive normally, at this rate we can only guess it's the gearbox and others reckon it is too, but it's hard to explain what is happening unless you are driving it. It will sometimes just jolt and carry on as normal for a moment if keeping my foot down, but this feels like an ongoing issue and a scary one in fact, it's happening in 5th as well as every other gear too. It happens on whatever road wherever, it will always kick in going up little ramps in the road and I've tried everything I can to test it out, driving in higher gears and lower, going certain speeds (it doesn't actually happen much around 5/10mph...) and if anything driving normally? we are stumped. Would anyone have an idea?

First of all I must say that I'm not professional by any means and I could be wrong but that sound like it could be a clutch/gearbox related problem. Did you try to press the clutch pedal while driving and then slowly letting it bite, or maybe letting it faster while driving ?
 

That's what others are saying, they reckon gearbox too, I've tried double clutching when driving and nothing, if anything when I've gone to take off in first a few times when finding my biting point it has juddered hence why I have had to quickly just rev and then change gear, it's not juddering as if it was about to stall either, it's like a jolt and judder! nothing crazy or major but you can feel it! it is scary when it happens, as it sometimes does it around roundabouts which is where we thought I was going too fast or in too high of a gear, but I've lowered the speed and gears and nothing has really changed. I've tried putting the clutch in and out but nothing either?

Edited 26 October, 20223 yr by kays04polo

Since you are mentioning that your speed drops but the rpm are staying constant then its most likely a clutch slipping problem. You can do a quick google search and find how to test if your clutch is slipping. Basically you throw a high gear (5th) while going at a constant speed in a big straight road. Say you have 5th gear doing 50 and you maintain 2500rpm. You then press the clutch to the floor and slam on the accelerator while the clutch is pressed. The rpm will jump to redline. Then you release the clutch and the rpm should return to 2500-2700 instantly. If it takes time for the rpm to drop or if they don't return to where they were before pressing the clutch, then your clutch is slipping. 

 

Do a google search or watch a video tutorial to understand how to do this. 

we’ve had a look and the problem was actually the 02 sensor! It’s all fixed and hasn’t done it since! 
thank you everyone for the help and suggestions!