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[Diamond Black Geezer]

haha. Yes, bring forth the opinion of the OOF Yodas.

Car advice good offer they...

[Webby the Bear]

Regulate the pressure the FPR must.

[TheBoy]

Hmmm, not convinced on FPR. Omega ones are bulletproof.

I'd be looking for airleaks.

[Diamond Black Geezer]

That's the route I've been heading down. I've sourced almost a complete set of replacement air hoses etc.. And those not replaced have been checked.

Next job is the 6 x O-rings where plenum meets the 'trumpets' as they may have been letting a little past or the plenum may not have been mated properly. So far areas checked for leaks are

-Main vac hose - checked, but replaced
-All thin vac pipes replaced (excluding two to reservoir at pollen filter - these on the 'to do' list)
-All elbows and straight rubbers to thin vac hoses replaced.
-ICV changed twice
-EGR re-sealed to plenum, with hylomar and gasket

Is there anything else left to change to do with airleaks?? 

[Webby the Bear]

i agree with TB that the FPR's are bullet proof. never heard of anyone on here having a problem with one.

However, having had small vac leaks myself i know that they dont increase your idle speed to 1800rpm! yes, the idle does flicker because the mix is being constantly adjusted with the introduction of pirate air (gooold for the price of silver) but not to that scale ime.

at the very least check fully the hose that goes from ICV to FPR. Is it definitely seated on the FPR? etc.

[Diamond Black Geezer]

Yeah, that's what's completely confusing the hell out of me, that veryyy high erratic idle! I will definitely check the ICV to FPR hose, and replace.

Failing that, basically, I'll be replacing the 'plenum assembly', I'll call it, with that 37k one from the Scrappy. At a stroke that replaces the plenum, seals, TPS, EGR, throttle body, breather bridge and seals, and four pipes off the back of the breather bridge, hose from FPR to ICV, everything.

I know thinking scientifically I should be replacing one part at a time, but as several parts in the above list are a bit 'suspect' or at least I'd like to change out of piece of mind anyway. Replacing it as a whole lot means I'm not breaking any seals, or disturbing much. I don't see any point in taking the breather bridge off, throttle body, hoses and ICV to then fit them to my crusty old flaking paint plenum, when they're already fitted by Opel, and nicely mated etc...

OK, just now jumping to the biggest, nastiest scariest thing  - could it be the ECU?

[05omegav6]

Nah, the ecu fuels the engine according to what the sensors are telling it, not the other way round... Any ecu issues would soon result in non running or misfires.

Any chaffing of the icv loom is the only electrical issue that might cause the problem... Ecu is bombproof unless you microwave it

[Entwood]

Given that the RPM is always doing the same and almost constantly high .. and rpm is governed by the amount of air getting in .. (the ecu just adds fuel to make the air fuel mix correct) .. is it possible that the throttle plates are not fully closed/damaged ?? If excess air is getting past the throttle plates then that could cause the high RPM ??

What could cause the throttle plates to be ever so slightly open/passing excess air ?? As its not a DBW then throttle linkage wrongly adjusted ?? bent shaft ?? burrs/damage to outer edge of throttle plates ? scratches in the throttle body ??

As it is steady (ish) until warm .. could the expansion of the throttle body as it warms up be linked to the problem ??

Just guessing and throwing ideas at you to be honest ..

[Diamond Black Geezer]

Thanks for that... I only thought because of this low mileage one in the scrappy - so an excellent change to get an ECU, immobiliser etc... if needed. SO long as I know it can't be that, that's great 

I am debating getting the ABS ECU, though, as a friend had an issue with his TD once, and you need to get one off the same year (or at least PFL, MFL or FL) and engine size, and gearbox. And mine being a prefacelift 2.5 V6, they're a bit thin on the ground these days for specific parts. Everyone's got either a 3.0 Elite or an MV6 on here! 

Sorry, I digress. I did hope it was a sticking throttle body, but looking at it that's fine, runs super smooth. So... there's every chance that after I fit the 'new' plenum and all the other bits, that the problem will be cured.... however, knowing how she's been a mardy cow with me lately, I suspect the issue shall remain... where else should I look for airleaks? Because I can't think of anywhere...remembering that when the main vac hose and plenum was blanked off it still did the erratic idle thing...hmmm....

[Webby the Bear]

At least with the ''donor'' car from the wreckers you got some bits for swapping that was probably dirt cheap. Did you get the inlets / fuel injector assembly that you can swap over to rule out FPR?

And like Nige says.... check the throttle assembly to see if its possible its stuck open somehow

[Diamond Black Geezer]

And thanks Entwood (as well as Webby and The Boy, of course)

Well hopefully as the 'plenum assembly' gets replaced that will identify one way or another it being the TB. There is a little gap when the butterflies are closed - we're talking fag paper or less, which seems the same as the throttle body I got off Missy MV6, but no idea just how fine a tolerance a closed TB is, if you see. I mean to a joiner, a 32th of an inch is nothing, and will close up fine, but to an engineer, that's a chasm. As I say, when the new TB goes on, this should prove one way or another. And as luck would have it, I have two throttle bodies to choose from! 

[Diamond Black Geezer]

Mr The Bear - I din't get the fuel rail, inlets etc... no. It's on the cards, I suppose. Knowing I won't be able to get in until the weekend, but my next night on the car is weds / thurs, I can change all the rest, then always move onto these bits, if needs be. Not a massive job taking the plenum off.. I'm starting to enjoy it actually

[Diamond Black Geezer]

As a sub-note - I did notice the throttle body screw (which I assume should have a single slot in it) has half the head snapped off.  So someone's been there before... it's possible me or father turned it a bit, the last time it came off (when the cam covers were done, 2 years ago, but it was never run afterwards) it does seem to be at the limit of its adjustment, strangely...