V6 Low idle revs in D whilst stationary

[davebngy]

Hi all, very grateful of help and advice from anyone on this:

I've read a lot of forum post on the V6 with low idle revs whilst stationary and the engines under load i.e A/C on or in D.
The revs start over 1k when cold, drop to just under 1k when warmed up. Then through driving or turning on A/C and sitting in D etc. it gradually will drop down to 500. At times it can recover but not always. I've seen it drop even lower once or twice but hasn't yet stalled.

There is a noticeable wobble at times when the A/C is on. Not constantly but now and then, which is why I started to investigate.
One thing to note is that the van was stolen and recovered recently. So it could have been driven hard at that time. I don't recall this happening before.

I've examined the throttle body at the rear of the engine. Removed all the pipes from it and all seems clear and clean.
I removed the item circled yellow in the image below. It was a little gunged up with black goo however nothing terrible. Cleaned with carb cleaner.
The valve (i think it is) circled in red allows airflow in only one direction, I believe as it should.


All spark plugs have been changed but were pretty clean.
The offside rear HT lead has oil residue on it upon removal. No pooling down in there but I'm aware there is a weep from the rocker cover gasket.

The throttle cable has been tightened up now also though I doubt it would have any baring on this.

I have a new distributor cap and rotor arm arriving tomorrow as well as replacement HT leads.
Someone mentioned Lambda sensor to me. Could this be the culprit? I've not seen in mentioned in the other idle issue threads I've seen.

I'm due to leave in the van this Friday with family so quite worried and hoping I can fix before then.

Many thanks,
David.

[g8dhe]

I had a the same experience recently and it was a combination of several things, cleaning the throttle body, replacing rotor arm and cap, new leads eventually cleared all the problems. However one word of warning if you run it for any length of time (return trip from Devon to Sussex) was sufficient to put enough unburnt fuel thru the Cat to destroy that as well, so try not to use it whilst suffering erratic idle rev's!

[davebngy]

Many thanks for that info and wise words. Those parts are on their way to me just now so fitting tomorrow as well as the Lambda probe. Universal Densu part DOX-0109.

I've wondered about an Idle Control Valve (ICV) and seen it mentioned in relation to 2.0L, located at the front. I cannot find one on the V6 though I might be missing it. I did wonder if it was below the throttle body however I'm not sure.

Below pictures of the removed parts. Slight white bits on the recessed contact and the arm does look an interesting colour but I haven't ever looked at these before and cannot be a good judge.

[davebngy]

Hi all,

I managed to work out that this was ultimately a missfire likely on a single cylinder. The HT Cable's, rotor arm and distributor cap seem to have fixed the problem. I was also told that the Lambda probe could be at fault so I replaced that too.

I also tried using the wire and volt metre method to check for error codes on the ECU but there were none.

If you have a V6 which isn't idling well when warm then amongst other things, it could be these components. As a pack, I purchased and replaced all at the same time. My van has done 76k miles. I'm not sure if this is standard or not for that mileage.

The offside rocker cover gasket is leaking a little too. Causing a small amount of oil to get into cylinder 5 (rear). It's possible this damaged the plug and the lead and got me to this fault. So it will need to be replaced asap also.

HT leads are straight forward to replace on the V6 if a little fiddly to feed through. You need the centre cover off as well as the seat covers up. Mainly for the routing of offside cables over to the nearside where distributor is.

Rotor cap is a pain as it's a Philips head and hard to see. Stick your phone in to take a pick.

3 bolts on the distributor cap. Two at top and 1 underneath.
Remember it's plastic and tight is tight but too tight is stuffed!!!!

Lambda probe you need for V6 is expensive from most sources. Google the Denso DOX-0109 this is the universal one that I learned will fit the V6. If not the same for others then please comment. However you can go to this site and select Mazda MPV II 2.5 V6 and you will be directed to this part.
https://www.denso-am.eu/e-catalogue/

It comes with 4 wires whereas the Bongo OEM part had 2. Disregard the 2 black wires and connect the white and blue. I.e. splice them to the OEM connector ready in your van. Make sure to insulate the black wires though. I used some heat shrink and electrical tape. If you want a photo let me know.

This has been a bit of a nightmare for me as I had put it into a respected garage and asked for them to put right all the issues that had come from my van being stolen. Unfortunately this didn't happen. I've learned a hell of a lot just in poor circumstances. Hopefully these words will help others.

Feel free to ask if you suspect something similar and have queries about the symptoms my bongo was having.

[Bob]

This is really valuable info.

Many thanks for taking the time to write it up and add photos.