Easy fix, but not chep. Dump the factory ECU and go Aftermarket. Full programmable, something that gets a reference from the TPS and manifold pressure. This will surely cure all problems. Also check that the cats are not blocked, the fuel filter is clean, the injectors and all associated wiring and in top order, and maybe replace your dizzy, as the modules on these are known to be a problem. Mine used to do something similar, but aftermarket injection fixed that problem
Brett

Well the last thing to do is the injectors...will pull them off when I have a chance and have them cleaned/reco'ed if necessary and let you all know what happens....thanks again to all who have made suggestions...has all been valuable information and immensely appreciated, cheers

Hmm I would be going against the flow here but I really think it would be your best bet to take it to Ford and just let them look at it and let them know the symptoms. They will look at it and will diagnose it for you and if the first guy that looks at it has no idea then he will ask someone more senior. It would save you running around & spending money replacing all that other stuff. I had the same problem with my XF just trying stuff here and there because one day it just stopped working perfect. 3 months later took it in and told him what was wrong and what I had done. 15 mins later he rings me and tells me my head gasket is blown, yet I had spent $$$ on new plugs, leads, cooling components and other rubbish with the carby and what not.... just a thought though

i had a 200rev fluxuation at idle and chased it,i wanted a spare coil so i ordered one,a week later i tried the new one.presto idles at 850 rpm exactly,am keeping the old one for spare-break down. try a new dizzy cap ,if yours is cracked will miss on cylinders and hard to see by eye,i had a few in the past. every thing else is new or checked excepf the above? coil about $45-50 dizzy cap not sure

Hmm every 45 secs or so if Im at traffic lights my car will "jump" 200rpm..I just assumed it was the ISC but maybe I should replace the coil & cap. Its done 170,000 but runs oh so smooth

Well I'm stuffed is the latest !!!! Got a set of reco'ed injectors (flow tested, oringed etc:) put them in yesterday...high hopes came crashing down...still f@rt on goosing the throttle and worst of all...you have to wind it over for about 5-6 seconds EVERY time to start it, when it finally starts it does the old choof choof bup bup and then settles down into a quite reasonable idle...go figure ? It had done the starting thing a few times recently (maybe every 10th start ) but since the injectors it is EVERY time... I'm hoping its not the injectors but that I've upset something else in the process that has created the problem. I'm going to check everything over again today.

Disconnected the fuel pump and ran engine until stopped.... reconnected pump 20 mins later and engine fired perfectly... diagnosis - leaking injector/s. Who can you trust these days ? Reco'ed injectors, flow tested, back flushed...yeah right...clean em up and ship em ! Old injectors back in, starting up fine... original problem still exists however, but I think I would say its not injectors...
So at this stage...

List of what its not:
---------------------------------------------
- spark plugs or leads (replaced with new)
- MAF sensor (cleaned and then replaced with 2nd hand)
- fuel filter (replaced with new)
- ECT sensor (voltage checked ok)
- injectors (replaced)
- oxygen sensors (replaced with new)
- TPS sensors (voltage checked ok)
- distributor cap (visually sound)
- air filter (clean K&N)
- timing (base timing checked ok @ 30DBTDC)

List of suspects:
---------------------------------------------
- fuel pump or regulator (although pressure checks ok - 38-40psi)
- ECU (rare chance)
- 2nd Hand MAF sensor (even rarer)
- some mechanical fault - head gasket, valve, etc: (seems unlikely)
- normal behaviour from 5.0L (I hope not)
- some form of alien/gremlin/spirit possession (most likely!!!!!)

The car has been timed with a G-Tech over the 1/4 and averages around 16.5 to 16.9 which seems reasonable to me as it is stock as a rock minus a K&N and cat back twin system (no extractors). Maybe it should run better but I really don't have anything to go on...does anyone else have reliable figures for a similar car?

it could be fuel pressure reg. what pressure have you got after the reg?
if there's too much pressure going to the injectors, it will squirt more fuel in each time.
if they're not dear, i'd replace it.
if you could also borrow a dizzy and an ecu, that would eliminiate the big things.

mines 261000,still strong

Well, nothing much to report except that the problem is getting worse, can definitely feel the slight miss when taking off from standstill/idle now, once revving though it doesn't miss a beat... this seems to be getting worse along with the starting (winds for a long time when hot) which to me indicates a leaking injector/s. I have ruled out the secondhand MAF now (tried a mates with no change), so it looks like I might have to chance another set of injectors - throwing up whether to go new or reco'd. Can get reco'd for $110 or new for $360... what do you guys reckon... I'm leaning toward new...

what you have said i dont suffer any of that in my EB V8 302w only probelm i had was clunk in the downshift in my gearbox after all things changed turned out to be the ECU, b4 you go pulling your hair out get your hands on a known working 100% ecu thats the same as yours.

Also distributor cap could have a hairline crack and that can do s**t.

sounds to me like the regulator or the pump output , when you checked the pressure did you take the vacumn line off?......try disconnecting your o2 sensors and run it this will open circuit the computer and it will estimate the mixture setting on the rich side and see if that affects it at all?.......or try squashing the return line hose with some pliers etc and see what that does? (slightly)

Well I did ring an ECU repairer just recently about the issue, he was 100% that it wouldn't be an ECU fault, he'd seen a few different symptoms but definitely nothing like what I was having, and I was inclined to believe him, being consistent behaviour like it is I don't think I'll mess with the ECU... I have also backprobed the ECU with pretty good results there.

I'm having similar problems!!! my mate is testing my maf out on his EL Series 1 XR8 so fingers crossed. If the maf is fine, then I am going to blow the car up and get a BA XR6 Turbo....

have you run through a tank of fuel and refilled?

could be bad fuel and stuffing up injectors, and other fuel system components.

do test by bypassing the fuel tank.