A few weeks ago I started getting an erratic idle, initially it was dropping down to 200 rpm approaching roundabouts, having owned the car for 10 years I know this is a classic MAF symptom.

So I replaced the MAF and reset the ECU but the symptoms didn't go away only changed. The idle revs wouldn't drop below 2K and gradually went higher and higher etc. Pointing at the idle control assembly being at fault. Sure enough the IACV was covered in oil/sludge. I cleaned out the throttle body and this seemed to work reasonably well but still this erratic idle persists. So I buy a used idle control valve and change it, reset the ECU and it is exactly the same.

I've also tried changing the lamdba sensor and the air filter but still this has had no effect at all. The car starts cold and idles at 1600-1700 until it is warm and then it drops to 1100-1200. The car will sit at 1050 idling ok, but if you blip the pedal it seems to go into a high low routine. The revs drop and rise between 1200 and 600. The car used to idle at 850 on the nail steady as a rock.

Anyone any idea what the hell it is? The airfilter box cover doesn't provide a brilliant seal could this be it? It's on the original TD04 Turbo but has done 125000 miles, could this be on the way out. Oh... one more thing there are no error codes reported.

It's driving me nuts, any help appreciated.

 

Good luck finding the solution mate, I'll be watching with baited breath as I'm having similar problems with my 55000 mile bug

I'd be looking for an air leak which is my next port of call although I checked the plugs today and they were a lot looser than when I fitted them so I'm hoping that may make a difference

 

Sounds a bit like there's an air leak there somewhere, have you checked all the boost pipes.

 

Yep an air leak id think. Possibly the o/e hard intake pipe has cracked/split

 

Is the OEM pipe prone to cracking?
Is intake pipe easy to get out? I should be able to check for play on the turbo impeller at the same time. I'll try and check it out tomorrow. Thanks

 

Aftermarket dump valves can make your idle erratic and fluctuate, worth a thought if you have one fitted?