Fiesta 1.3 revs cycling

first look for an air leak on the intake side

ISTR that Ford came up with a modified TPS harness to overcome symptoms like that on the Ka and Fiesta with the 1.3 donk.

This is an old bugger - s reg. Not had a chance to look under bonnet since OP, for air leak suggestion. Will do Mon.

Same OHV "Endura E" engine though.

Going to have a look in a bit - and we have two suggestions - air leak, and harness probles - what should I be looking for with a wiring problem - some sort of electronic idle valve?

Go with Mr Cheerful's suggestion first. Checking for an air leak won't cost you anything and he is an experienced technician who has seen hundreds of examples of that engine.

My own suggestion is based on (my wife) owning a Ka for several years. The Ka had the same engine as yours. The symptoms were exactly the same as yours. It was definitely Throttle Position Sensor (TPS) related. I recall there being a service bulletin on the subject. I suggest you Google "Ford Ka TPS harness". You will get quite a few hits including this:-

Ford Ka 1996 on Fiesta 1995 - 2001 1.3 Endura

Problem: Engine revs hang up when changing gear.

Solution: The problem could be a corrupt throttle position sensor (TPS). This is due to a poor electrical contact at the connector. The solution is to fit a revised sensor wiring loom and connector. A revised wiring loom has been fitted since 09/2001.

HTH.

Yep, I have an X reg 1.3 and had these symptoms. New wiring harness resolved the problems.

Ok, I had a play and discovered the following

1) What stupid car that you have to take the battery out to get the sir filter box out! But anyway, no apparent air leaks.

2) I didn't know it was a TPS when I played with it, but that seemed to be the only thing that affected the rev rates prob - and unplugged or not didn't seem to do anything much different, apart from when refitting it when engine running - shall have to investigate the wires more - I thought it was because I was blocking/unblocking an air hole. Also stripped and cleaned the idle control valve - whole thing is a bit better now, but I see it was messing with TPS that has helped not idle.

There's a Fiesta in a scrappy 500 yards down the road, might just go rip off the TPS.

Thanks

the air leaks if any will be around the inlet manifold (anything engine side of the throttle valve assembly) check for them by spraying carb cleaner around and see if the revs change.

from the net: this is someone with the tps fault I was trying to solve this problem for a couple of days and found what causes it. I have an 1998 fiesta with the 1.3 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.

Cheers