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[Webby the Bear]

i've never heard of a TPS going bad mate (not to say they cant of course)

[Diamond Black Geezer]

Fair enough. I can 99.999% discount that, then. Thanks  Got one on the plenum, and other bits I got of Missy MV6 a few weeks back, that's all, it was just a thought, as I'm sure someone on here recommended cleaning or changing one once. It's logical. The engine revs up, ECU says' whoa, too fast, slow it down.' it slows it down, then says 'woa, too slow, speed it up' and so on... fauly sensor could be causing that malady.

Really hoping its the top hat seal. It wants changing, anyway, brittle, hard and found it wasn't even seated properly. It's a £1.20 seal for god's sake - why didn't my dad just change it when he last refitted the breather bridge. GRRR!!  Though how the hell that should be causing the engine to rev gentle up to 1300, then hunt between there and 1800rpm I have nooo idea! 

[Marks DTM Calib]

Be aware that there are at least two different throttle pot types on the V6 and fitting the wrong one creates interesting effects

[Diamond Black Geezer]

Ah, thanks Mark, do you mean a difference between the 2.5 and 3.0 throttle body, or are we talking about the throttle bodies with DBW throttles on the 2.6 / 3.2s? The TP sensor I've got as a 'spare' is off a long plenum 3.0 with cable throttle, if that helps?

You're just the man I wanted to ask a Question of, actually - In this case would you advise replacing the 6 x O-rings?

They seem ok ie: very slightly proud of the machined mating surface of the dividers. So in theory should seal between divider and plenum fine... I am sure I've read one of your past posts / how-tos saying these don't tend to need replacing. If this is a possible cause of the engine woes, then change them I shall.

[Webby the Bear]

If youre positive the leak is in the inlet manifold you can replace breather bridge gaskets (top hat and two o rings), the 6 inlet to plenum 'o' rings and finally the gaskets on the upside and on the below side of the black plastic sandwich plate.

at least if you did the lot you can rule out your leak being one of them.

imo

[Diamond Black Geezer]

Got the top hat and the two tiny ones of the breather bridge, theyre in the kitchen  ... the 6x O rings inlet to plenum + possible, yes, may just order some. I was just trying to picture the "gaskets on the upside and on the below side of the black plastic sandwich plate." got ya, the dividers, in black plastic, yes.
I'd tend to say 'no, can't be them' - but if I don't, then reassemble and it's the same - do I take it all apart agin, to then replace them? Probably not! So may be worth doing, as you say...

[05omegav6]

Worth checking all the bolts are nipped up, but using your logic, you might as well change the thermostat,  oil cooler and camcovers while you're at it... Just in case

[Diamond Black Geezer]

Well, last night's 'progress'...

Just about managed to clean up and fit a replacement plenum, ICV, and throttle body. Off a scrap 2.5, and in excellent order, having covered just 37k miles. I used my own breather bridge, as the other looked like it was a little clogged - rather than spend time cleaning this I opted to fit my original known good one, replacing the seals on it as I went.

I checked the ICV to FPR hose, as advised by the good Mr Bear, just in case this was causing issue. there appeared to be a dodgy split, but after testing this by blowing into it under water this appeared to be a perfectly good hose, no air leaks. As I didn't have a spare, I refitted.

Things I noticed along the way...
-The 'top hat' seal was snapped and incorrectly fitted. Again, I was hoping this was the cause of the bad idle. However...
-My current throttle body appears to have an incorrectly adjusted butterfly valve - no idea how! I was hoping this was the reason for the bad idle. The new one has never been adjusted since the factory, it appears, which is good.
-Some pillock snapped the electrical connector off the new plenum (me), so the old one had to be re-used
-My old plenum is ever-so slightly different in shade and overall condition, can you tell?


Adjuster screws


Snapped connector


The living room carpet, a mint, and a slightly-less mint plenum.

Though they seemed fine I replaced the 6 x O rings underneath the plenum with the low-mileage ones, just because. That was it for last night, finished at gone 10pm, and elderly neighbours not massively keen on a V6 revving when they're trying to sleep, strangely.

Got up early, fitted the EGR this morning checked all hoses and connectors, then fired her up.

Worse than before!!!! Slightly lumpy running, and the EML light was flashing - four pulses, if this means anything? ARRRGH!!! One step forward, two back 

[Varche]

The Persians would be turning in their graves with that lot on their hand woven beauty

[Diamond Black Geezer]

Made from a rare and beautiful creature, apparently known as a Crylic. 

[henryd]

Christ,if I had an engine to bits on the living room carpet it would have gone dark very quickly for me in our gaff

[Marks DTM Calib]

That throttle butterfly stop should be adjusted so the throttle butterfly is fully closed but not sticking (if allowed to return to far they stick), nothing to clever about setup on that one and easy enough to check. I have seen some vehicles where the professional bodge boys have wound the throttle stop in to mask an ICV issues (more common on the older 2.0 16V 4 pot X20XE). Under this condition, the ICV has to work almost shut and you can get some interesting idle rev conditions.

One of the issues you now face is that there has been a lot of bits done to the engine, so its time to take a systematic approach to things.

So start at the air filter and work through the inlet setup to the plenum, check for leaks and split flexi hoses, make sure the MAF is in the correct way round and the air temp and multi ram connector are correct (as on earlier cars you can fit them wrongly although this does not impact idle hugely).

Now check the branch from the bag pipes to the ICV, check its secure and ok and make sure the ICV is seated well and tightly in the plenum.

Now onto the EGR, is it fixed well to the plenum (to often ham fisted people who don't believe in torque wrenches over tighten the 3 bolts here and strip the threads in the alloy plenum). If possible, blank the EGR off to totally remove it from the equation.

Now check all the breather system, start at the breather box behind the 1-3-5 head and inspect the pipes closely, I have seen the larger breather pipe split close to the breather box before which is a tough one to spot sometimes.

Make sure the breathers are connected properly and that the auto box breather (if auto) has not been connected by mistake.

You sound more confident that the breather bridge to plenum joint is now ok.

I also recall you checked the brake servo pipe to but worth a second look over.

As a rule, the small breather pipes don't create an idling issue as any air leak associated with them is pretty small when compared to the large gasps of air each cylinder takes.

If after all this things seem ok then its deeper into the valley we go....

And read your codes again.

[Diamond Black Geezer]

Much appreciated Mark.

Me working off the premise that 'well it must be one of the things associated with the plenum', changing that over complete should have cured it, albeit without knowing the specific fault.

I will go over the bits you list methodically. I'm also going to run her for a period of 15 mins, too, just to get up to temp, in order to see if she still does the erratic hunting idle as before. If that's cured, then at least I'm only having to sort a lumpy idle (which may yet me down to eg the recent rain we've had, the water leak which may have contaminated a plugwell, or similar.)

Thanks again Mark. I loose count of the pints I owe you so far for all your help, but whenever I'm in your neck of the woods I'll let you know and unload a crate on your doorstep   

[Kevin Wood]

Me working off the premise that 'well it must be one of the things associated with the plenum', changing that over complete should have cured it, albeit without knowing the specific fault.

It's much better to inspect a component and find a fault (or not) than to simply substitute it, assuming that any fault must have been fixed in doing so. These cars are getting old now, so 2nd hand parts are getting old too, and can't be assumed to be OK, so you risk incorporating new problems in addition to the one you're trying to fix.

[Diamond Black Geezer]

Yeah. This is true. I knew at the back of my mind that was the danger, but to be honest the list of parts replaced or fitted goes like...

almost all thin vac tubes
every thin vac tube rubber elbow
Battery
ICV 2x
Main servo vac hose 2x
Breather bridge gaskets

Plus and the visual inspection of what feel like every single visible engine component at least three times over, so I am started to get impatient, just want her to run normal, so I can start with the other jobs, like suspension, rust, refit all the hanging off and missing interior trim, tyres, Mot etc..   

Lesson learned.