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Car Keeps Over Revving When I Accelerate? So Confused


baker181
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Hi guys, this is my first forum post and hello to everyone on this forum 😊

To start things off I am having some trouble with my car lately and the problem is forever getting worse by the day, I will start off in first gear and everything is normal, acceleration is normal and the clutch bites instantly, but when I hit 2nd gear if I do it quickly the revs will stay up at 4500 - 5000 rpm, so I have to depress the accelerator to bring it down to its right revs, as soon as I put a little pressure on the accelerator it revs right up to 4500 or higher again. The only way I can accelerate is by dabbing at the accelerator which is very frustrating.

I have done a few clutch tests, such as putting the car into 3rd as I am stopped and releasing the clutch so stall it and it does stall when I do this, I ain't very knowledgable on cars myself, any help on this or recommendations would be brilliant, getting very stressful now, thanks a bunch guys, I an upload a short vid clip to show you better to

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First thing to look at is your footwell carpet/mat. I found a long time ago that they can slide up behind the pedals and stop them from returning to fully up after you push down. Something simple, but can be easily missed.

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Either that or possibly a hose split or similar causing an air leak on the induction side of the engine.

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What age fiesta is this? And what engine? I just repaired a customers car doing same thing

Sent from my iPhone using Ford OC

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Here's the fix, not cheap though if same problem, test and check everything before changing.

If 1.25 Zetec Se engine or 1.4 zetec Se

But basically unrelated to cause of your problem but makes it worse... Check PCV hose under inlet manifold... They split and collapse, this introduces an air leak that makes revving problem worse.

Next, check right hand side of engine... If you have antifreeze leaking your coolant temperature sensor is a write off... This is what is causing your problem primarily.

Coolant temp sensor fails, ecu reads cold, dumps excess fuel into engine.

This in turn has fouled your spark plugs... You will probably find them black and wet.

So now you have a build up of fuel and improper ignition... Next what happen is the massive build up of fuel starts burning and pulling air through pcv system causing the revving.

So coolant temp sensor and spark plugs if same problem experienced will fix revving problem.

But also it will also have fouled up lambda sensor, so test this also because a working lambda sensor will normally compensate for failed coolant sensor to a degree.

So possibly looking at pcv hose, spark plugs, coolant sensor on right hand side of head... Not one under plastic thermostat housing

And lambda sensor if failed.

But first 3 are primary cause of the revving.

This customers car was terrible if you turned engine off it was so flooded after it wouldn't start for at least 5-10 minutes.

Sent from my iPhone using Ford OC

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Hey thanks for the help, I will check on all things to see what is going on, and my car year is 55 and it's a 1.4 Zetec petrol, cheers

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No problem, worth checking above.

On this particular customers car, 1.25 but essentially same engine. Revs would suddenly rise up to 5000 rpm and stay there, wouldn't drop at all.

Only way to stop engine self destructing was to turn it off... But then it was so badly flooded it wouldn't restart for a good 5-10minutes.

Removed the spark plugs and not only was they black but completely wet, dripping in fact with petrol.

So changed new set of spark plugs and lambda sensor as that wasn't working which helped dramatically with the problem, was almost gone ... Didn't rev up to 5000rpm any more but did occasionally hang for a second or 2 at 3500 before dropping. So then changed the coolant temp sensor on right hand side of cylinder head ( think on your engine it maybe down where spark plugs are... They moved it I think.

And that fixed the problem completely.

So basically what was happening was,

Coolant sensor had failed... Engine ecu thought engine was cold; so it was over fuelling the engine. This blackened the spark plugs so they wasn't igniting the fuel properly.

So fuel was building up and up in the cylinders until it self ignited and was fuelling the engine with throttle closed... Seemed to of been pulling air through the pcv system. But because lambda sensor was faulty it wasn't compensating for the faulty coolant sensor and also reporting a lean mixture which was also causing extra fuel to get dumped into engine.

So check coolant sensor, I think it's between spark plugs 1 and 2 on your engine, make sure it's giving a good reading and not a false one.

Then check spark plugs, if they haven't been changed on a recent service change them.

Then check lambda sensor is switching correctly between rich and lean every 1-1.5 seconds or so.

If it was an air leak it would Rev funny all the time from moment you start engine and not intermittent which leads me to believe it maybe a similar problem to what my customers car had.

Forgot, also check throttle position sensor, if it thinks throttle is open when it isn't that will also cause sticky throttle symptoms.

No need to change stuff guessing, just use above as pointers on what to look for and test each thing.

If you don't have suitable equipment then download forscan and buy a modified elm327 adaptor with switch and you can see what sensors are doing.

Sent from my iPhone using Ford OC

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