Fiesta Mk6 (1.4) idle issue.. one for the experts

[Lach]

Hi all, got what seems like an unsolvable issue of my fiesta.

The car is a 2005 preface lift fiesta 1.4 zetec (petrol) on 80,000 miles. I bought the car as a non-runner 2 years ago and since got it back on the road and gave it to my wife. I've always had an issue with the car not quite ideling correctly. Its somtimes slow to start in the mornings and on idle it has a sporadic "jolt" (just a small one but can be felt when sat in the car) from the engine. The car reads no codes and drives absolutely fine. I've changed the ignition unit and all 4 HT leads. brand new and correctly rated battery. All spark plugs are new and gapped to 0.9. oil, oil filter, air filter and fuel filter and new as well. All vac lines where removed and pressure tested and have no holes. Vacuum was tested at 22" on idle and passes the throttle blip test. Fuel pressure sits at 48psi and holds on idle and from the pump with engine off. Pressure leaks down at about 2 psi a minute with engine off. I've cleaned the throttle body and cleaned the MAP sensor. 

 

The revs sit at 1500 cold and between 900-1000 warm. There is a subtle hunting/fluctuation of the revs of about 75 when warm. The car has started to develop a top end rattle also sporadically when warm and is not fully in time with the engine nor dose it increase with revs. Whether this is related or just another fault I've yet to determine. 

The cars due for a service so I'm going to try a 5w30 oil as stated in the hand book to see if it helps.

I'm not sure what else to check from here so any advice would be most appreciated.

 

Thanks 🙂

[Paulkp]

If you have checked all the "normal" things, then look at the switch inputs to the ECU.  Power steering pressure switch, Clutch switch, air con compressor switch - these (if fitted to your car) do have an input to the idle.

On a '98 Zetec Fiesta we had, it came back from a Ford dealer with an intermittent idle - traced (by me)! to a torn out connection to the power steering switch.

Good Luck., 

[Lach]

12 hours ago, Paulkp said:

If you have checked all the "normal" things, then look at the switch inputs to the ECU.  Power steering pressure switch, Clutch switch, air con compressor switch - these (if fitted to your car) do have an input to the idle.

On a '98 Zetec Fiesta we had, it came back from a Ford dealer with an intermittent idle - traced (by me)! to a torn out connection to the power steering switch.

Good Luck., 

Hi Paul, when I changed the clutch in December I did notice the power steering pressure switch had a broken wire, which I have subsequently fixed but to no difference. The Aircon pump spins when selected , so I feel that's in good order. I've previously searched for the clutch switch but according to where it's ment to be fitted there is nothing on my car, so I assume not all fiestas have it?

Thanks

[Paulkp]

The Haynes manual for the '98 Fiesta has an engine management diagram (15) for the 1.4 petrol showing a clutch switch and power steering switch, and an input from the AC cycling switch - unfortunately the Haynes manual for the 2005 Fiesta does not have any engine management diagrams!

However, fig 2.7 in Ch 6 for the clutch does show what appears to be a switch, but I don't know what engine was in the car that Haynes were using - and the same photo is in the Fusion handbook, although in the Fuel and Exhaust chapter it states the the Power Control Module does get a signal from the clutch switch.

No other bright ideas from me apart from swapping the PCM, or the actual electrically controlled throttle.

As an aside, I once had an intermittent misfire on a 2.9 Sierra - eventually traced to the throttle pot which had a worn track - funny thing was, with the throttle pot totally disconnected, the car drove as normal !

[Lach]

20 hours ago, Paulkp said:

The Haynes manual for the '98 Fiesta has an engine management diagram (15) for the 1.4 petrol showing a clutch switch and power steering switch, and an input from the AC cycling switch - unfortunately the Haynes manual for the 2005 Fiesta does not have any engine management diagrams!

However, fig 2.7 in Ch 6 for the clutch does show what appears to be a switch, but I don't know what engine was in the car that Haynes were using - and the same photo is in the Fusion handbook, although in the Fuel and Exhaust chapter it states the the Power Control Module does get a signal from the clutch switch.

No other bright ideas from me apart from swapping the PCM, or the actual electrically controlled throttle.

As an aside, I once had an intermittent misfire on a 2.9 Sierra - eventually traced to the throttle pot which had a worn track - funny thing was, with the throttle pot totally disconnected, the car drove as normal !

Thanks for your thoughts Paul. Interesting about the clutch switch I'll see if I can hunt something down. Could be my problem is that it's missing..

[Lach]

On 2/13/2019 at 10:33 PM, Paulkp said:

 

Okay so after another look I found the clutch pedal sensor, I realised I've not actually looked for it on this car.. I had another fiesta Mk6 before this one lol.

Now to my understanding you shouldn't be able to start the car with the clutch up and the switch pressed, however the car starts indicating a faulty switch. Now after I removed the switch the car still continues to start but surely as the ignition circuit goes through this the car should not start at all?? I've tested the switch with a multimeter and confirmed it works perfectly. So looks like the circuit for this switch has been bypassed.

[Paulkp]

Not sure what the clutch switch does on this age of car with a key start ?  It may just cut the fuel off between gear changes, and not a "Stater inhibit".

[TomsFocus]

Clutch switch is just for the PCM to smooth gearchanges on the mk6 (raises or lowers revs to match road speed).  

These never do seem to idle perfectly tbh.  Throttle body or TPS would be most likely here though.  Cleaning the TB isn't always good enough.  Might also be worth checking lambda readings as well.

[Lach]

Hi guys, sorry for the slow reply. I've been working with the wiring to the after market alarm system fitted as there was some exposed wires on it. So far it looks correctly installed just a sloppy job

[Paulkp]

Thanks for the update, keep trying!

[Stuffy]

On 3/11/2019 at 12:42 PM, Paulkp said:

Thanks for the update, keep trying!

I have the same model car with the same issue. The car displayed a grey code showing control module VVS output "a" which is an abs sensor. Have yet to replace it but was wondering if yours may be related. Looked on a website for that code and it says that an faulty abs sensor can cause rough idling. Hope this help.