1996 1.1 Fiesta over revving

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Intermittent fault. Any body got any ideas why the engine starts over revving when I depress the clutch.

posted by  barryrim

More information would help. How much does it "over-rev", does it happen everytime, happen at idle, happen when shifting? Ect, ect.

posted by  DodgeRida67

It doesnt happen all the time but when it occurs, its usually when changing down. As you take your foot off the accelerartor and press the clutch in, the engine revs at about 2000 rpm.
It can happen when changing down from 4th to 3rd, 3rd to 2nd etc and also when stopping, again as I push the clutch in.

posted by  barryrim

Hard call. Sticky linkage...faulty TPS... 1996 Fiesta?... :ticking:

posted by  DodgeRida67

Bought this a few weeks ago for wife. Seemed ok on test drive but now has similar over reving problem when clutch depressed (3k to 4k rpm) wife hadn't noticed. Car also runs on, when foot is taken off accelerator, takes a long time to slow down, alomst like 'cruise' but without the 'control'. Tick over, when in neutral and stationary, is a little high 1000 - 1200 rpm but engine revs normally i.e. revs rise AND fall in-line with accelerator movement.

posted by  badknee

I had same problem on a ka, it turned out to be TPS, throttle position switch was not registering idle position, using gentle tap on one side of housing once loosened screws and using digital voltmeter I set it to lowest voltage, dont remember exactly but think it was 0.6v or .08v, it reset it self to normal idle again and been okay since.

posted by  chatterbox brit

If your Fiesta has an IAC (idle air control) valve or solinoid on the throttle body it may be carboned up and needs removed and cleaned or replaced. If so equipped it should have an electrical plug going to it so make sure that is clean and functional too. My niece has a 1991 "Festiva" and I got wrangled into replacing the clutch that was destroyed by oil from the leaky valve cover gasket. It was then I discovered that the Festiva was manufactured by KIA (Korea) for the Ford Motor Company. :cussing: Yikes!!!

posted by  PTT1

I think he's probably scrapped it by now lol.....although if anybody else has this problem, feel free to reply :ohcrap: :thumbs:

posted by  Cliffy

I was trying to solve this problem for a couple of days and found what causes it. I have an 1998 fiesta with the Endura-e engine (the same is one installed in most KA cars):

- it is caused by the throttle position sensor (tps) - a small black plastic piece with a three-wire plug which is located on the back side of the throttle body.

- in my case it was not faulty because i've taken it out and measured it with an ohm-meter, nor was the connector faulty. I've read that sometimes the connector itself can fail, and that there exsists a revised one.

- it was the wrong resistance of the tps in the idle throttle position that was causing it - it seems that this is a design flaw and that TPS is set to work near the "edge" and over time when the material changes its properties this causes it to go over the ege - and overrev.

The TPS in endura-e is a potentiometer which is connected like this:

- one pin is connected to the minus (chasis)
- the second one is connected to constant 5 volt source from the ECU

- the middle pin is the slider and changes the voltage as the throttle turns. When you turn the key (give a contact) and measure the voltage between it and the chassis in idle, it has to be 0.4 V. In my case it was 0.55 V

You can adjust this sometimes by loosening the screws on the tps and moving it to the side (it has a little play)

What I did (and I don't recommend it :) is to solder a 5k ohm trimmer pot between the slider (middle pin) and a minus pin (the brown wire in my case) and with it I can regulate the idle voltage from 0 to 0.55 V and by experimenting i could clearly see:

- if I set it above 0.4 V it has a tendency to revv a little longer
- if I set it above 0.48V it is overevving madly
- if it's at 0.4V - its fine

Of course you shouldn't turn the trimmer too low not to short-circuit the ecu source, and if it's set too low the engine might have a tendency to stall at idle. AND NEVER DO THIS if you don't know how to fit it firmly and to insulate it properly.

First try loosening the screws (just a little) with a star screwdriver and tapping the tps so that it moves in the same direction where the throttle turns when increasing the gas. Be careful not to spray the tps with wd 40 because it will make the problem even worse (it affects it a little) and if you're removing it remember to look carefully where the axle sits in it's slot because if you mount it back just a little off it could make it worse.

PS My car is still sometimes stalling when idling, but I think, This is an another problem (with the idle air control valve)

Hrvoje

posted by  hdagelic

Thanx for the info...:thumbs:

posted by  Cliffy

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