'00 4.0 V6 SOHC - Revs surge every 6 seconds

[The Limey]

Hi,
I hope that you can help as there seems to be very little (free) information on Explorers over here (England).
I have an '00 Explorer North Face, I think it's based on the XLT?
Whilst idling, the engine revs surge about every six seconds, not enormously but enough to drive me crazy and for pedestrians walking in front of me to think I'm about to run them down.
I guess they jump about 4-600 revs typically.
I ran a search on this and brought back some info on MAF Sensors but that only seemed to be the case for cold engines. Mine is continuous.
Also, I recently bought a PCV valve from e-bay (because it was there!!!) - can anyone tell me what it is for?

Many Thanks!

 

[Howard]

Welcome to another UK owner.

I would start by cleaning your IAC (Idle Air Control) do a search and there is a good thread on how to clean it. Cleaning the MAF wouldn't hurt either. As for the PCV (Positive Crankcase Ventilation) it is all to do with reducing hydrocarbon emissions and it is located on a rocker cover. Basically you just pull it out and if it rattles then its working. You can test the pipe for vacuum too. Just disconnect it and use your finger. Vacuum = working.

 

[The Limey]

Hi Howard,

Thanks for your advice on this, I'll run a search on IAC now. FYI, I had it converted last year to run on LPG - it's a Nicholson Mclaren multipoint kit and so far seems to be working without incident. I have a 90 litre tank which costs c£30 to fill up and I get roughly 240miles from it (could get more I'm sure but do a bit of urban cycle and lots of motorway driving)
If there are any obvious mods that I should do to it then please let me know. Although I'd love to have it as a toy I don't off road so I suppose my focus would be on smooth running odf the engine and economy!

Regards,

Ben.

 

[Howard]

Does the surge happen when running on petrol or LPG?

 

[The Limey]

Hi,
It happens on both Petrol and Lpg, the only other thing that I've noticed is that it does probably tick over a little low - sometimes this is c500rpm, would this cause it to surge? it tends to dip slightly before surging to 1000/1100rpm.

 

[Howard]

I still think that its IAC related. Have you checked that yet ?

 

[The Limey]

Hi Howard,

been away hence the lack of response.

I've done as you said and followed the threads for cleaning both the IAC & MAF sensors and Bingo!

Thanks for your help with this.

Ben.

 

[Howard]

Glad it all worked out ok.