Revs dropping at idle

[Greggo]

Hi, I've got a 1.6 sx model and the revs are dropping at idle. It idles about 700 rpm normally when warm and if I come to a stop before idling the revs drop very low to about 300, sometimes stalling. If it doesn't stall it keeps hunting from 500 - 700.

Having air con on alleviates the problem and stabilises the idle.

I've removed and cleaned throttle body and changed air filter, but issue remains. The workaround is obviously to always have air con on, but not practical all the time.

Is there any other areas to check?

Thanks

 

[Connorg115]

Unplug the MAF sensor and see if problem persists

Could indicate a dodgy MAF sensor or a vacuum leak

 

[IMBezza]

Is unplugging supposed to work on Mk1? My car shuts off when MAF isn't plugged in.

I had the same issue with my 1.8, idle was poor for a long time until the car decided to give up in town and start mis-firing for no good reason. Air con would stabilise the idle. I replaced my MAF with a genuine Bosch unit and she's been running perfectly since!

My car had the added bonus of the MAF causing a misfire and the engine going nuts in its' mount. If you've had a misfire check all your pipes for cracks or breaks. Mine cause a vacuum leak when it broke the pipe running from the air intake to the back of the manifold.

 

[Connorg115]

Is unplugging supposed to work on Mk1? My car shuts off when MAF isn't plugged in.

I had the same issue with my 1.8, idle was poor for a long time until the car decided to give up in town and start mis-firing for no good reason. Air con would stabilise the idle. I replaced my MAF with a genuine Bosch unit and she's been running perfectly since!

My car had the added bonus of the MAF causing a misfire and the engine going nuts in its' mount. If you've had a misfire check all your pipes for cracks or breaks. Mine cause a vacuum leak when it broke the pipe running from the air intake to the back of the manifold.

I had dodgy idle on my cupra r unplugged maf and put car into a sort or best guess mode

Eliminated the problem to either maf or vacuum leak for me I then smoke tested and then saw smoke pouring from inlet manifold

 

[Greggo]

Bit of an update in case it helps anyone. The revs continued to drop when coming to a stop after engine was at temperature and hunting between 300 (sometimes stalling) and 650 rpm but to workaround problem I just kept air con on and this stabilised revs higher. They still dropped at a stop but it didn't cause any problems.



The issue started manifesting again on cold morning because the air con won't come on when it's cold so I was getting the same problem again.



Throttle body had already been cleaned but I didn't align it originally ( didn't have VCDS or even know about it to be honest) but I got the software scanned with no errors so did another clean and alignment.



Didn't solve it unfortunately.



I had purchased a fuel filter as I wanted to start servicing car so I fitted that one afternoon. This definitely improved matters, the revs did drop, but then returned without hunting. So this was better, but it still threatened to stall. On a whim I plugged back in after doing a bit of research that said EGR valve could be issue and I recalibrated the EGR.

This appears to have solved it having tested for a week now without using air con to mask the problem. I know I should also clean out the EGR, but will do that when I do the rest of the servicing at weekend.

So it seems it was EGR related!

 

[mty12345]

EGR valves are a pain in the ass. Failures often cause high idle speed or stalling.