Revs surging at idle

28774 Views 151 Replies 29 Participants Last post by Jgray2016, 3 mo ago

Jgray2016

Discussion Starter · Dec 1, 2020

Bit stumped here. I’ve taken car to Ford and they’ve reported nothing wrong. I’ve no engine management light either.

Problem: car revs surge when down at idle. Say the car idles normally at approx 700/800rpm. All of a sudden however, the revs will drop down to 500 and the car shudders, revs jump back up to the normal idle, then drop back down to the 500, then jump back upto normal idle.

It seems to happen randomly, but a sure way to induce it would be to have the A/C turned on when approaching a stop. Once you stop it’ll do the double surge thing then go back to normal idle.

Anyone any ideas? Is it a load issue? Should I try replacing the battery?

81 - 100 of 152 Posts

Jgray2016

Discussion Starter · #81 · 11 mo ago

10

Further snips:

normal revs idle

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high revs (1500 ish)

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Jgray2016

Discussion Starter · #82 · 11 mo ago

4

further pics

normal idle,

Font Technology Screenshot Number Software

uncommanded 1500 rev idle

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Jgray2016

Discussion Starter · #83 · 11 mo ago

i honestly have no idea what to look at in the above. if anyone has any ideas, please do share.

@Crevarius FYI, finally got an OBD reader

Reactions: 1

Crevarius

· #84 · 11 mo ago

Whoa! Those fuel trims are messed up! I’ll look at this more tonight after work.

Reactions: 2

Pezzar

· #85 · 11 mo ago

You replaced the complete purge valve and lines?

Jgray2016

Discussion Starter · #86 · 11 mo ago

Pezzar said:
You replaced the complete purge valve and lines?

Not sure if it's complete, but it looks like a little cylinder with a run of plastic hose either side of it approx 300mm long either side

Crevarius

· #87 · 11 mo ago

Your readouts still look so much like my evap failure… Can you get short term fuel trim readings too, please?

I will finish checking these against the Ford specs tomorrow; it was a long day of work.

Edit: I will go datalog mine tomorrow morning too, so we have something besides a spec sheet to compare against.

Reactions: 1

Jgray2016

Discussion Starter · #88 · 11 mo ago

3

Crevarius said:
Your readouts still look so much like my evap failure… Can you get short term fuel trim readings too, please?

I will finish checking these against the Ford specs tomorrow; it was a long day of work.

Edit: I will go datalog mine tomorrow morning too, so we have something besides a spec sheet to compare against.

Much appreciated @Crevarius

Just dug up all the parts I tried replacing too. I also did the high pressure fuel pump and the throttle body.

Evap purge

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1 of the O2 sensors (not done the other)

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Fuel rail pressure sensor (replaced twice)

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Jgray2016

Discussion Starter · #89 · 11 mo ago

3

Any idea how I would detect if the self sealing gas cap is actually sealing properly? If not the evap purge, maybe it's pulling air in somewhere? But presuming that would throw an EML/CEL

When idling normally, A/C off

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Uncommanded high idle, A/C still off

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ki

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Ucsniper

· #90 · 10 mo ago

How's this going? I'm having similar issues. If I run the car with the front O2 unplugged, it runs beautifully, just get the check engine light. I reached o2 but still same rough idle, yours sounds slightly different being high idle, like maybe accelerator position sensor or throttle body. I'm thinking about replacing my throttle body, curious how yours is coming?

Reactions: 1

Jgray2016

Discussion Starter · #91 · 9 mo ago

Ucsniper said:
How's this going? I'm having similar issues. If I run the car with the front O2 unplugged, it runs beautifully, just get the check engine light. I reached o2 but still same rough idle, yours sounds slightly different being high idle, like maybe accelerator position sensor or throttle body. I'm thinking about replacing my throttle body, curious how yours is coming?

I replaced my throttle body entirely and made no change saldy. I've not tried replacing the accelerator pedal yet though. It houses both the APP (accelerator pedal position) sensors. Reason I've not replaced it is because it really should throw a check engine light, but I will probably try it at some point

TechJessica87

· #92 · 8 mo ago

Usually self revving is a faulty gas pedal ❤

Reactions: 1

Jgray2016

Discussion Starter · #93 · 8 mo ago

TechJessica87 said:
Usually self revving is a faulty gas pedal ❤

Replaced pedal but no difference sadly. Suspecting
issue between sensors and instrument cluster and ECU now. It's weird how A\C on or off affects my issue. I think there's some issue between low speed high speed can data getting to the ECU. Something is messed up. Car had an aftermarket immobilizer in it previously. Wondering if a wire was sliced that shouldn't have been! Lord know how to find out though!

Crevarius

· #94 · 8 mo ago

Jgray2016 said:
Replaced pedal but no difference sadly. Suspecting
issue between sensors and instrument cluster and ECU now. It's weird how A\C on or off affects my issue. I think there's some issue between low speed high speed can data getting to the ECU. Something is messed up. Car had an aftermarket immobilizer in it previously. Wondering if a wire was sliced that shouldn't have been! Lord know how to find out though!

Damn, I was hoping that would be it. I'm nowhere near my car for another week or two, but when I am maybe we can do a MS teams/Skype call and compare readouts again.

Reactions: 1

Jgray2016

Discussion Starter · #95 · 8 mo ago

Crevarius said:
Damn, I was hoping that would be it. I'm nowhere near my car for another week or two, but when I am maybe we can do a MS teams/Skype call and compare readouts again.

I am better prepared now... I have a obd cable and Fordscan 😁

JamoRS

· #96 · 8 mo ago

I don't know how you haven't torched this car yet......must be extremely patient.

Reactions: 1

Jgray2016

Discussion Starter · #97 · 8 mo ago

8

JamoRS said:
I don't know how you haven't torched this car yet......must be extremely patient.

It's one of those things. It's not a major issue, it's just annoying if I'm sitting at traffic lights etc.

But yeah, if it was any other car, it would have been sold by now! 😂 I live in rural Scotland, so I'm minutes away from roads like the below. Car is just the best car I've ever been in for this type of environment. Nothing else comes close in the corners

Sky Vehicle Car Automotive lighting Mountain

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Reactions: 1

JamoRS

· #98 · 8 mo ago

And I thought Australian road surfaces were dogshi7!
Some of those look like goat tracks! 🐐
All the best getting it sorted out mate.

Reactions: 2

Jarett

· #99 · 7 mo ago

Jgray2016 said:
It's one of those things. It's not a major issue, it's just annoying if I'm sitting at traffic lights etc.

But yeah, if it was any other car, it would have been sold by now! 😂 I live in rural Scotland, so I'm minutes away from roads like the below. Car is just the best car I've ever been in for this type of environment. Nothing else comes close in the corners

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Did you ever figure the problem out? I have the Same thing happening

Jgray2016

Discussion Starter · #100 · 6 mo ago

Jarett said:
Did you ever figure the problem out? I have the Same thing happening

Sadly not. But today I just happened to open up my engine compartment fuse box. There's debris inside, looks like the lid hasn't/wasn't sealed correctly. Could this have been the cause of my issue all along? Debris and grim is close to the front end of the box, where the ECU/PCM relay and fuses are...

Can it really be that simple? I don't want to pull any fuses out, as it looks like there could be corrosion/don't want them to snap.

Surely any fault in the fuse box though would throw a code?

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