pampy

OK, I'm now desperate and pleading for some help with my son's 2000 (W) reg 1.25 zetec Fiesta - (his appears to be the later 2000 model which the Haynes manual doesn't seem to cover very well).

We started off with a high idle and and what some describe as a "throttle flare" when the car is stationary.
Basically we've replaced the Throttle Position Sensor twice now (first time with a pattern part then with a genuine Ford item). Initially the problems were cured by fitting the pattern part and resetting the ECU by disconnecting the battery for 30 mins. However, the problem then returned - car idles when stationery at 1200 rpm, then "hunts" between 1900 and 2500 rpm if you blip the throttle. Put the car in gear and just move slightly and the revs drop back to idle again. When moving it's as though it has "cruise control" and wants to drive itself. We've now fitted a new genuine Ford TPS, and rectified a problem with a collapsed vacuum pipe which was causing the revs to stick at 3000rpm but still have the problem. Immediately after reconnecting the battery the car would idle at 1000rpm, but once you touch the throttle it's up to 1200 and then hunting again between 1900 and 2500rpm. I've checked the wiring to the sensor and the voltages - 5 volts in from the ECU, one pin to ground and the output back to the ECU on the centre pin at closed throttle is 0.2 volts (I'd read somewhere that over 0.4 volts can cause problems).

After some more experimenting last weekend we thought we'd nailed it down to the Idle Control Valve so I've just fitted a brand new item with a new gasket and, if anything, the problem is worse The idle is even higher and the revs are now hunting between 3000 and 4000.

Please, has anyone got any other ideas ? My son is driving me mad moaning about having to keep spending money on it and I just don't know where to look next. He did have a garage hook it up to a diagnostic when the problem first appeared but they didn't find any fault codes.

Thanks for any help or advice anyone can offer.

JonathanJ

This is one of those problems I sympathise with you over . as my step son has just bought a 51 plate fiesta 1.25 and it had several issues that we have had to work through with the same moaning about cost and time .

You seem to have worked through several things that are logically correct , but you mention several things of interest , one if you move slightly it goes back to idle , no fault codes present , iscv replaced and now seems worse and tps replaced twice .

No DTCs would suggest no faulty sensors , as in failed , but one is possibly giving an unexpected result

The fact that it improved after replacing tps and resetting ecu but as soon as it had read the sensor map it went back to the same would suggest it is trying to prevent stall or something else

The fact that you say that if you move car it then drops but then I assume as soon as it comes back to standstill , it does the high idle again might suggest vehicle speed sensor but seems a bit far away from core issue to look at .

If I was you I would try and understand where the idle speed is being fed from , you have replaced iscv , I would try removing it from manifold and block the 2 holes and see if it idles low or at all , or is still idling high to remove that as a possible cause , then I would check the throttle is fully closed during the high idle , it may well illuminate the engine light as you will loose the maf flow but if plate is shut and iscv removed it has to be a vacuum leak in the manifold or gasket and the situation is as soon as you move the vacuum leak is "overpowered" by the required air so until the vacuum is built up again and the threshold of gasket or crack is reached it is ok again .

If you think it is a vacuum leak in the manifold and all pipes seem ok then carefully at idle spray some brake cleaner CAREFULLY and lightly in small areas around the manifold , if it gets sucked in and the idle speed fluctuates and the resultant smell from the exhaust would trace it .

It is always difficult to diagnose this type of fault , just stand back and think "where is it getting the air " then look around carefully .

Hope my babbling helps in some small way .

andysfatrs

Assuming the car has power steering, have you tried following the power steering lines and finding the pressure sensor. Then test the wiring for this as the ecu will up the engine speed dependant upon steering pressure load, if this breaks they will idle irratically and high.

Worth a shot

pampy

Thanks for the advice - I do have a small update.

After posting yesterday, and speaking to a mechanic friend, I desperately went in search of a vacuum leak as it appeared to be the only thing left that it could be. So, I removed and cleaned the throttle body (which was in pretty good nick actually), cleaned out the PCV valve (just in case) and then removed the one thing I hadn't disturbed until then - the MAP sensor which sits next to the Idle Control Valve on the inlet. It looked pretty dirty so i gave it a blast of electrical contact cleaner, dried it off and refitted it. Now this is the later 2000 1.25i engine which Haynes seem to have totally ingored in their manual despite it's quite obvious differences in the inlet side of things so I wasn't about to go blindly into removing the inlet manifold at this point.
Having re-assembled everything I went to start the car to show my neighbour exactly what the problem was - and, surprise, surprise, it idled and ran perfectly !!! I restarted it a couple of times to check that it really was ok, then went indoors pretty pleased with myself and texted my son to tell him it was fixed. Three hours later, just before my son was due in from work, I popped out to check it again - started it up and the fault is back, just like before

So, now we're thinking MAP sensor - obviously cleaning it had an effect on temporarily remedying the problem, but as soon as it get a bit dirty again its failing - does this sound plausible to those in the know ?
We've cleaned it out again this morning and got rid of the fault again, but on the second time of starting the fault is back.

Mind you, here we go again with another fifty quid part, so I'm just looking for someone to give me a steer that we are on the right track.

Thanks for all your assistance, it really is most appreciated.

mazza3115

hi, sorry to revive a really old thread thought this would help someone who had the same problems, as i had spent hours reading forums... i have a 1998 mk4 fiesta, after getting the car back after a clutch change from a garage my car was over revving ie. clutch in when driving (any speed) the revs would increase until i put the car in gear or at a stop it would sit at around 2-3k revs and after 20 or so seconds would drop down to below 1000. i ordered a new throttle position sensor and after fitting it the revs were still high and my obd reader was showing throttle position at 18%. long story short i broke the sensor by trying to position the sensor fitting with a pair of pliers...(little did i know that if i had of left the new tps fitted as it was and disconnected the battery for a while the car would have learnt that the tps position was idle speed and the revs would have sat under 1000) anyways a trip to a scrap yard and another TPS and just incase an idle control valve all for a tenner, when fitted and the battery disconnected to allow the ECU to Learn when reconnected. taadaa fixed my over revving so far.... fingers crossed

pampy

Blimey, this was a long time ago now. The Fiesta is long gone now, replaced by a MK6 Zetec S Fezza, then a Civic Type R, and currently a Focus ST2.

Anyway, just to close the book on the Fiesta fault - it turned out to be a split vacuum hose underneath the inlet manifold. After tearing my hair out with everything else a simple repair with super glue and gaffer tape sorted it out and the car ran perfectly for the rest of the time he owned it - and all of the time my sister owned it after him.

Now my time is spent looking after my ST170..............