Fiesta 1.25 (1999) over revs when coasting

bledd

bledd

bledd

Don
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I picked up a friend's Fiesta to do an oil/filters/plugs service before dropping it off for an MOT.

Whilst driving it, I noticed that when I took it out of gear to coast towards a junction, the revs would slowly rise up to ~3000+. As soon as the car reached a halt, it would return to normal revs ~1000 ish.

It also felt like it was pushing itself along more than it should have, could quite happily sit at 40/45 on a long flat in 5th without any weight on the accelerator.

Again, the revs are 100% normal whilst at a standstill.

The symptoms were there all the time and are not sporadical.

Any ideas?


Fiesta 1.25 zetec
 
I had a similar problem with a 96 1.8 16valve escort it went into the dealers numerous times without ever finding the fault. Changing the throttle position sensor seemed to help for a short while but the problem was never fully fixed
 
Hi there

1. MAF is detecting more airflow due to coasting and as such increasing rpm's.
2. You have a vacuum/air leak.
3. Remove intake, clean the throttlebody with carb cleaner and clean the maf with maf cleaner, put it all back together ensuring everything is tight without air leaks.
 
Wouldn't an air leak make the idle funky too though?

It never coughs or 'hunts' for an idle. On another Fiesta I've had an air leak problem before, that was indeed a split air hose that was causing the problem. Symptoms feel very different.

I've just read about the same problems I'm having being caused by damaged wires on the power steering pressure switch..
 
bledd. said:
Wouldn't an air leak make the idle funky too though?

It never coughs or 'hunts' for an idle. On another Fiesta I've had an air leak problem before, that was indeed a split air hose that was causing the problem. Symptoms feel very different.

I've just read about the same problems I'm having being caused by damaged wires on the power steering pressure switch..
Click to expand...

Sometimes, but not always, there may be nothing wrong with your car, it could just be normal.

My Jaguar S-Type if you coast it will do the same, as the MAF is detecting increased airflow.
 
MatteH Oxford said:
How would the air get past the (nearly) closed throttle plate?
Click to expand...

MAF is in front of the throttle body.

Your air filter takes in the air, the MAF is positioned after the air intake to detect the airflow, the throttlebody then comes after this.

But I suspect your car is fine, my Jaguar is an S-Type and shares many Ford components, its normal on the S-Type, so suspect your car is OK.
 
Gibbo said:
Hi there

1. MAF is detecting more airflow due to coasting and as such increasing rpm's.
Click to expand...

Coasting would not make the MAF detect more airflow. Engine speed and load determine the airflow, not vehicle speed.

The problem is most likely caused by the power steering pressure switch or the connector/wiring to the switch being faulty (i.e. open circuit). This causes the ECU to believe that there is always demand on the power steering and it increases the idle accordingly. This gives no engine braking and makes the car pretty horrible to drive. The switch is located on the underside of the steering rack, on the offside of the car.

Note that on Fords of this era, the engine RPM will increase a little when coasting with the clutch engaged (i.e. foot off the pedal), but it shouldn't be as high as 3000 RPM (maybe ~1500 RPM)
 
If you have your foot completely off the throttle then it doesn't matter if the car is stationary or going 100mph, the maf (possible a MAP i think for a 1.25 depending on year) will not detect an increase in airflow because there is nowhere for the air to go. Think of holding a tube with a block in the middle of it, out of you car window when going along at speed - does air flow through it?. Nope!

OP likely has a problem with the TPS sensor, I suspect the ECU is not seeing closed throttle properly. Or see above REF PS switch
 
Gibbo said:
Sometimes, but not always, there may be nothing wrong with your car, it could just be normal.

My Jaguar S-Type if you coast it will do the same, as the MAF is detecting increased airflow.
Click to expand...

It's really not normal behaviour, I guess I'm not explaining it well. The car feels like it's pushing itself more than it should when it's in gear and moving.

I get the feeling that if I left it out of gear whilst coasting, the revs would keep rising until they reached the limiter.

-edit, I stared typing this before the last two replies came in, forgot to click Submit

edit2, yes; there's no engine braking, meaning you have to knock it out of gear when approaching things. Yesterday was the first time I'd driven this particular Fiesta, only had to slow down for 2 junctions, so didn't notice the problem at first.


My wife used to own the same model, so I'm not alien to how they should drive.
 
Last edited:
bledd. said:
It's really not normal behaviour, I guess I'm not explaining it well. The car feels like it's pushing itself more than it should when it's in gear and moving.

I get the feeling that if I left it out of gear whilst coasting, the revs would keep rising until they reached the limiter.

-edit, I stared typing this before the last two replies came in, forgot to click Submit

edit2, yes; there's no engine braking, meaning you have to knock it out of gear when approaching things. Yesterday was the first time I'd driven this particular Fiesta, only had to slow down for 2 junctions, so didn't notice the problem at first.

When the Jag was doing this, I thought it was not normal, I had the intake heads off, changed all the gaskets like 2-3 times thinking I had a vacuum leak. In the end took it to a Jag specialist who said what I was describing seemed normal, I was like really, they took it for a test drive and confirmed yes perfectly normal. As such I now drive the car and it no longer bothers me now I know its the norm.

Maybe ask a Ford technician and see what they say. :)

My wife used to own the same model, so I'm not alien to how they should drive.
Click to expand...

I thought it wrong my Jag did it, so much so I had the intake manifolds off, air intake the lot 2-3 times changing gaskets etc. thinking I had an air leak. In the end took to a Jaguar specialist who confirmed the car was fine and was perfectly normal.

Check with a Ford specialist, see what they say. :)
 
It wont, its just a leak, it has no self awareness at all.

A lot of ECUs use a road speed signal to determine when it is time to start the idle program (ie revs drop down to idle speed as you come to a stop). The fact the revs on this come back down when the vehicle comes to a stop indicate to me what the idle control process is actually working ok, but when the ecu isnt set to "idle", the revs shouldnt rise, so that plus a vac leak, is causing the revs to come up.
 
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