Technical 1.2 Dynamic over revving at idle...

[Wazzzer]

Took the wife's Dyanamic out for a run the other day and after getting up to temp it decided to idle at about 1200rpm. Nothing I could do made any difference.


I've just plugged in Torque and read the upstream O2 sensor values and it oscillates between 0.1v and 0.9v as it should with the rear reading at 0.8v.

Has anyone experienced this before? There are no fault codes

 

[koalar]

search the forum. Load similar. Lots of different causes

is yours fly by wire throttle or cable operated.

Read the ambient temperature before you start the car.

Read the expected vs actual RPM's

Air leaks are quite common as well as sticking idle valve.

Did it start doing this suddenly or got worse over time.

Does it ever drop to 800 RPM.

 

[Wazzzer]

Thanks for the reply. I did have a quick look but there was nothing specific and no real solution.

It's cable operated and this has gradually got worse over time. It had a new genuine Magnetti throttle body fitted around 2 years ago.

Expected rpms are always around 800 but actual is higher. It's fine when first started but once driving around for a bit and coming to a stop it rarely sits back down to 800rpm.

I'll plug it in to my laptop instead of the phone tomorrow and see what I get

 

[koalar]

make sure there's slack in the cable and its going fully back onto its stop.


Its not unknow for the internal spring return spring to brake. Should be nice and smooth as you twist the cam although I would doubt one would brake so soon.


As the expected is 800 RPM I guess the pedal sensor will be okay. But worth check while its hooked up. As said earlier check the ambient temperature sensor should be within a degree or so of what Google says the temperature at you local it.


I think the most likely will be a vacuum leak. Spaying carb cleaner around all the possible joints is normally the quickest way to find them.

 

[Wazzzer]

Brilliant thanks. I'll give those bits a go over the next few days and report back.

 

[Wazzzer]

make sure there's slack in the cable and its going fully back onto its stop.


Its not unknow for the internal spring return spring to brake. Should be nice and smooth as you twist the cam although I would doubt one would brake so soon.


As the expected is 800 RPM I guess the pedal sensor will be okay. But worth check while its hooked up. As said earlier check the ambient temperature sensor should be within a degree or so of what Google says the temperature at you local it.


I think the most likely will be a vacuum leak. Spaying carb cleaner around all the possible joints is normally the quickest way to find them.

Managed to get the Dynamic hooked up to the laptop today and had a quick look at some parameters...

Barometric readings were OK, requested revs OK but what I did notice was the air temperature reading at 27°C while Google was saying 19°C.

I don't know if this is because it was sat in the sun but it was definitely out.

Ironically it wasn't playing up while sitting there but I can guarantee it would if I took it out it would play up again.

I'll have to get myself some carb cleaner from Halfords in the week as I've used all mine cleaning out my vespa carb!

 

[koalar]

until you start the car the ambient air should be spot on.


its part of the MAP sensor


The panda does run fine with it disconnect. As far as I remember it doesn't over rev but runs slightly rich with it disconnected

 

[Wazzzer]

Ok that gives me a starting point then, I'll get a MAP sensor on the way and go from there

Thanks for your help so far!

 

[Wazzzer]

OK having a bit of trouble finding a genuine Bosch MAP sensor with the part number off her current one, does anyone know from experience if it has been superceded?

 

[koalar]

don't you have a 100hp as well ?


most fiat petrol are the same mines off a punto


you could swap them over to test First. A lot of problems are sorted by reseating anyhow.

 

[Wazzzer]

She's not having any of my parts!

Seriously though, good call. I'll go and check part numbers to see if I can swap over

 

[jackwhoo]

She's not having any of my parts!

Seriously though, good call. I'll go and check part numbers to see if I can swap over

Mazda 3 with cable throttle has a rubber boot that inner cable goes through as it leaves the cable outer. The boot falls off the outer which props the throttle open slightly causing high idle rpm.

Make sure you have a little slack in cable .

 

[Wazzzer]

Well touch wood she's sorted.

Managed to find a replacement genuine Bosch MAP sensor for £18 although not on the original number so it looks like it has been superseded over the years. For that price it was definitely worth a punt.

Fired straight up and behaved normally on choke then dropped to 800 with no sign of any hiccups.

I'll reserve full judgement until I take it to work on Monday but for the time being it looks like the cause has been found.

Many thanks to everyone who contributed

 

[Chali]

Problem solved ?

 

[Wazzzer]

Problem solved ?

I haven't managed to take it out for a proper run yet but the wife is going out tomorrow so I'm sure I will get a full report, good or bad

 

[Wazzzer]

So I'll bring this back to the top with the solution at long last!

After the MAP sensor was replaced I thought I'd cracked it. Seemed fine when I fired the engine up but after a quick drive the 1500rpm idle returned.

After a bit of head scratching I thought I'd replace the top lambda in case that was the issue. I found a relatively cheap Lucas version so went ahead and swapped them out.

No better, maybe a bit worse.

So I was out of ideas. Then I had a thought; it couldn't be the "new" throttle body... could it...?

So off to a breaker on ebay and found one for £17 delivered. Worth a punt at that price.

Swapped them over in about 10 mins with the ECU unplugged (I wanted the ECU to relearn with this other throttle body on there) and all seemed well like it always did on a cold start.

Took it for a drive to the beach today and it's perfect! Even the wife was impressed how smooth it was.

I'm annoyed yet pleased with the result and if anything the Dynamic has gained a few new sensors...

Case closed...

 

[DaveMcT]

Revving at idle is usually an air leak which could be caused by a worn throttle body.

 

[Wazzzer]

Not sure if this was a duff position sensor in the end but whatever it was it's gone now.

To mark the fact it finally works as it should i gave it a good wash [emoji106]

I've got a few little bits and bobs planned for it over the next few weeks, just to smarten it up a bit