Strange Idling

**poloplayer** · 15-10-2010, 08:55 AM

Hey guys,
lately I've been noticing that when the engine is idling, the revs constantly fluctuate. It'll stay around 700rpm, then up to 800, then back down, and occassionally it will rev itself a bit up to 900 where the whole car shudders a bit. The scary thing was that yesterday while stopped at the lights, it just shut the engine down, like it had stalled by itself. No warning, no shudder, no nothing. I thought it could be something to do with being APR'd but I switched back to the stock program and the revs were just as uneasy. Any ideas??

Thanks in advance

**Chuck** · 15-10-2010, 12:32 PM

do you have your car serviced regularly?

my uneducated guess would be dirty air filter

my scooter used to do similar things...but it was NEVER serviced in 5000kms

**noone** · 15-10-2010, 03:03 PM

It would be worth looking at the ECU through Vagcom. Without throwing a code and assuming it is serviced properly, it could be a vacuum leak or something similar.

By scanning for faults and looking at your fuel trims, you should be able to see most issues. It's not too difficult to look at the vac hoses for breakage and fiddle with the air hoses to see if they are fastened.

**MissVuks** · 15-10-2010, 06:51 PM

Perhaps it's your lambda probe?

**Hilal** · 15-10-2010, 08:39 PM

I'm pretty sure lambda sensors are only active when over ~3,000rpm. Even if you disconnect it, it would only display an engine fault light but wont affect its idle, but dont do that because u'll need to have it cleared by VW if u dont have the tools. Polo has two lambda sensors, one under the turbo and another after the cat.

Most cars have a idle air control valve, either its playing up or you have a vacuum leak somewhere. If you have a scanner, plug it in and see whats going on.

If you cant pin point the problem, disconnect your battery for 30 minutes and re-connect it and see if its any better.

**mrbrossnan** · 15-10-2010, 09:41 PM

hi,
check with vagcom, my guess is the pcv valve is busted? i had similar issue with my gti before..the rev was fluctuating like crazy while idling...gud luck finding the problem.

**poloplayer** · 15-10-2010, 11:40 PM

Thanks for the replies guys, yeah, I do get it serviced regularly. It was only serviced in April (for its 3rd annual service), so not really all that long ago. Should I get the guys at Volkspower (where I got APR'd) to check it out? Seeing as they might charge me an arm and a leg now since its no longer under warranty

**Lomo** · 16-10-2010, 02:35 AM

I'd try the Idle Air Control Valve first.

Here's a vid (sorry not a Polo) on how to clean it, it's a very easy job and you'll find the IACV somewhere around the throttle body.

YouTube - How to Clean the IACV- Idle Air Control Valve

Hilal, Lambda/oxygen sensor output is used for closed loop control at all RPM once the engine warms up.
If your car also hesitates when you put your foot down it may be the Lambda Sensor.