Fiesta ST150 idling/fuel economy

[firemunki]

• *I started this in the ford section but think it should be here as it is more tech***

Driving normally, not too many instances of ragging her nor driving like a OAP, what's everyone getting mpg wise?
My idling is still off when coasting at anything over 8-9mph, coming up to a junction and depress the clutch and it goes wild swinging from 500rpm to 1500rpm, and don't know if anything is "properly" wrong so just getting an idea. A couple post I can find on forums seem to point that this is a ECU issue and the software just does it and that's it.
I see around 26 - 28 going by my android app where all my costs are added in. This a bog standard 2005 ST.

It had a different throttle body fitted by the selling garage but then they didn't want to know. When I went to get my new front tyres they checked the tracking which is all within Ford specs. As he moved her on to their ramp he remarked that it didn't sound like she was breathing right. Their suggestions were a new air filter (in the post as we speak), some Redex through the fuel system (running through tonight when I fill her tank) and then spark plugs (not done yet as I thought I'd try the two I can do myself without buying more tools).

If that fails then they have suggest using a smoke machine to test for air leaks on the intake system.

Does anyone have any ideas I can try, ask them to look at, or just general ideas?

[trickywoo]

firemunki said:

I see around 26 - 28 going by my android app where all my costs are added in.

It had a different throttle body fitted by the selling garage but then they didn't want to know.

Forget the app use the tank brimming method and a calculator. 4.5461 litres to a gallon. Divide the mileage you get between fill-ups by the amount of gallons taken to get back to full. It'll be most accurate over a full tank.

Why did it have a different throttle body fitted. Was it a new replacement part or a modification?

The revving issue could point to a faulty MAF (air flow) sensor but this should show up on diagnostics.

Have you run a diagnostic check?

Other things worth checking are tyre pressures and if the brakes are binding.

[firemunki]

Hi,
It had a new throttle body as it wasn't starting properly. It would turn over lots but not start, they (the garage who I won't mention but suffice to say no one I know will go there now) at first said it was the battery but in front of the dealer after they charged it, she still failed to start so they said it was now the throttle body.

At this point they did say there weren't any codes showing but I've no way of checking (and with their "brains" they could be wrong), what/how do I check codes?

Brakes aren't binding that I can tell, and tyres are checked regularly and are at Ford's recommended pressure, the idling/mpg has happened on the tyres it came with and the new ones fitted in Oct when the garage mentioned the steps to try.

[firemunki]

New filter fitted, will see what happens now.

Anything else a home mechanic could try?

[firemunki]

Well it now idles at lot better if you roll along with clutch down so I think it must be a intake system issue. Only minor fluctuations now not more than 2 or 3 hundred rpm, unlike the best part of 1000 previously.

Odd thing being the car was serviced, according to the incompetent garage, not long before I purchased it so should have had a new filter.

[annodomini2]

Fault code read out.

My bet would be idle control valve, but that's a guess.

[firemunki]

Will try and get a reader, I'd hope it's not the idle control valve, that was the other reason they swapped the throttle body out!