Car Revving/accelerating Itself!

[stef123]

Yup live data will show throttle position sensor value so it's easy to spot if it's all over the place.

[jertum]

Thanks for all your replies - much appreciated. Still waiting on a call from the mechanic but will let you know how he gets on. Seems to be a common fault with these cars.

[jertum]

Just thought I'd update this thread.

I've had the Idle Speed Valve replaced and it appears to have fixed the problem! No more crazy revving or sticking throttle.

Hope I'm not tempting fate by posting this!

The only thing I'm worried about is if the fact that the battery was disconnected may be the thing that's solved the problem - i.e. sensors may have been reset as a result of this.

Oh well, fingers crossed the problem is gone for good.

[Lester1102]

I had a friend who decided to take his rocker cover off to be sprayed but when putting it back together forgot to put one of the seals back in and had exactly the same issue

[jertum]

Well, the car went over a year without having any idle/revving issues but it's back to its old self.

Had to get Green Flag out this morning as it would idle at about 1500rpm for a few seconds, only to then sputter out. Typically, when they arrived, the car started up and idled at about 750 rpm and drove around a mile absolutely perfectly.

I know this won't be the last of it. Here are a couple of theories:

1. I live up north at and the temperature dropped significantly last night. It was very foggy/moist this morning. Is there a chance that there was condensation on the spark plugs and this disappeared as the day got slightly warmer? I should point out that the car has been idling high intermittently even in warm weather after a long drive.

2. The last time the car started to behave itself was after a prolonged period of having the battery unplugged. As far as I'm aware, this resets some of the computer's settings and forces the car to 'relearn' the correct idle speed. Is this a good idea or could it cause more problems? I've also heard that removing the KAM fuse for a short period then reinstalling it could have the same effect. Does this sound about right?

Thanks in advance for any advice you may be able to offer.

[jertum]

Just had the same problem again. Scanned the car and it came up with the following fault codes:

P0693 - Powertrain

P0646 - A/C Clutch Relay Control Circuit Low

If A/C stands for Air Con then I'm completely puzzled as the car doesn't have air con. Do these fault codes point to an electrical issue rather than a vacuum leak or fuel delivery problem?

Thanks

[jeebowhite]

Yeah that seems to be the air con relay for sure...

Sent from my GT-I9195 using Tapatalk

[jertum]

So what does this mean? Can an air con relay cause idle/stalling issues? With it being a Finesse model, it doesn't actually have air con so maybe the ECU is reading it as something else? Thanks for your reply.

[jertum]

Booked the car in for a larger local garage to have a look.

One thing I noticed this morning is that it started up in very cold weather at around 1000rpm. This is quite strange as it would typically (when working correctly) start at around 1500rpm to warm up, then drop down to around 750rpm. Could it be that the car simply doesn't know what its engine temp is? Could this actually cause rough idle and cutting out? If so, what would cause this? Is there some kind of generic engine temp sensor or is there more to it than that? Would be great if somebody could fill me in before I take the car in.

Thanks very much for everyone's help so far.

[Mk4fiestaChris]

Hi, I know that this is an old post, but it is the most similar to problems I recently had.

A couple of weeks ago my Fiesta mk4 1.4i zetec started to get 'random' idle revs sometimes ~1200, but often going up to and sticking at 2500 or sometimes 3000. It would dirve Ok on fast roads doing 40-70, normal throttle response, but a right pain in slow traffic with the idle often not dropping below 2500, and stutering sometimes when pressing the accelerator. Also it was often difficult to start unless the fuel pump fuse was taken out for a few seconds (running v. rich at startup).

After reading many posts the most likely culpit seemed the idle control valve. I cleaned it and it seemed to work for 1/2 mile then back to random idle revs. Tried disconnecting the battery to reset the ECU, but mde no difference.

I invested in an F super odb reader and after setting it to com2, could look at the throttle values and IAC values. These seemed fine, but looking at other parameters I noticed the Engine Coolant Temp was reading -34! I had not suspected this as the dash coolant temp was working normally. The car has 2 coolant sensors one for the dash and one for the ECU. Disconnecting the wires from the ECT (under the coil) allowed it to run normally, apart from the radiator fan running. Changing the ECT sensor and all is back to normal.

I hope this post helps someone with similar problems to solve theirs - Get some live data and check everyting is working as it should!

[fleamoo]

'Automatic' revving at idle is a classic sign of idle valve sticking. What happens is that the idle valve sticks too far open, producing a high idle rpm. However, with your foot off the throttle the ecu sees the revs are high and assumes that the car is in motion but with no throttle (ie slowing down).So it cuts out the injectors as it normally would in that situation. This of course causes the revs to drop to normal idle, at which point the injectors are switched on again. But the idle valve is still stuck open, so the revs rise to a high idle again and the whole thing repeats. Hope this makes sense. Happened to my old Cavalier.

 

[Ethan M]

Hello, today I was rushing to work and when I went through a traffic light, all the sudden my accelerator went to 5000 rpms without me on the pedal. There's a weird flutter noise while driving and my check engine light is on and there a fan like sound when I push the gas pedal. I have a 2016 Fiesta ST, anybody got any ideas?