Right, I've realized the EPC light doesn't come on right away after I start the engine and start driving, that's because when the engine is cold the idle is perfectly fine at a steady 1100 rpm. After a short trip the temperature is where it should be but then the idle becomes really dodgy. I believe the term is hunting. It sounds like the engine is about stall but just in time it stabilizes itself. This is when the EPC light comes on.
Also, yesterday I stopped at a red light and when it turned green I didn’t give the car enough throttle so the engine stalled. I quickly started it again without problem but then the check engine light started flashing. I was in the middle of Stockholm so I had no chance of pulling over. The car drove nicely though and after a minute or so the check engine light stopped flashing and kept lit. Since then the EPC light has behaved the same way as before but the check engine light has stayed lit. 30 minutes without battery power didn’t help.
Today I found a post that caught my attention as it almost perfectly describes my symptoms.
The hunting and clicking is caused by a stuck vapor canister purge valve. The valve is on a vacume line. When it gets stuck open too much air enters the engine at idle or low rpm. This will cause the engine to hunt and stall as soon as any load is put on it if you do not rev it hard. The engine will over-run when coming to a stop and probably stall. It can come and go putting the chack light on. The quick fix is to just un-plug the solenoid. facing the enginebay it is located on the left hand side just infront of the suspention mount it is half balck half blue on every lupo i have seen. unpluging it will mean the car is driveable again but the check light does come on. It is 100% safe as long as nothing else happens that goes undetected because the light is already on. The part is about £70/80 from VW, they may or may not know what you are talking about but i would not bother going to VW. The part is easy to find at a scrapyards if there are Lupos / Polos. A number of other VAG cars share the part as well. Any other problems come along to clublupo.co.uk
I tried unplugging the valve but when I started the engine the idle went straight to 1200 rpm and the throttle didn’t work at all. I connected the valve again and the hunting continued.
I’ve noticed a sort of air sucking noise coming from the area around the throttle body. My current idea is that the TB is sucking in air that the ECU isn’t accounting for. I looked for split vacuum hoses behind the TB but I couldn’t see properly. I will take the car inside and check it later. However, I found something that looks like it should be connected to something else.
Here’s a picture. I’m thinking it might be a temperature sensor for the airbox. Could it have anything to do with my engine hunting?
This is how the engine behaves when it almost stalls. For some reason the idle was really really bad when I recorded this. Anyway...
Edited by P.Lindblom, 17 December 2010 - 10:08 PM.