Technical Punto MK2 stays revved

[crash25]

Hello, I have a 2003, 1.2l, 8v MK2 Punto. The problem with it is that when warm, and while revving past 1500rpm, it sometimes stays revved up even after I take my foot off the accelerator pedal.
For example, I was parked yesterday, with the engine idling at abou 800rpm. I then pinched the accelerator pedal with my foot, and suddenly the rpm went up to 3000rpm and stayed there. Turned off the engine, started it up again and it didn't do it again.
The problem is that this thing is intermitent, and it only does it with the engine warm.


I changed the throttle body with a new one, I changed the MAP sensor, the crankcase breather hose, airfilter and sparkplugs... but it still does it.
What else could be the cause for this?

 

[judderbar]

Hello, I have a 2003, 1.2l, 8v MK2 Punto. The problem with it is that when warm, and while revving past 1500rpm, it sometimes stays revved up even after I take my foot off the accelerator pedal.
For example, I was parked yesterday, with the engine idling at abou 800rpm. I then pinched the accelerator pedal with my foot, and suddenly the rpm went up to 3000rpm and stayed there. Turned off the engine, started it up again and it didn't do it again.
The problem is that this thing is intermitent, and it only does it with the engine warm.


I changed the throttle body with a new one, I changed the MAP sensor, the crankcase breather hose, airfilter and sparkplugs... but it still does it.
What else could be the cause for this?

I suppose you have the drive by wire accelerator pedal? There must be an electrical device at the pedal to alter the resistance detected by the ECU.

 

[crash25]

Hi, the accelerator is on cable.

 

[Brendan W]

Motor warm at idle, press the brake pedal and see if the speed changes.
Remove the airfilter housing.
Check that the cable is properly fitted at the TB and where it drops into the cutout on the battery side of the air filter housing.
Get someone to push the pedal and see that the throttle plate returns to the closed position freely.
Disconnect the small leg of the breather hose from the TB. Block and unblock the pinhole and see if it affects idle speed.

 

[crash25]

The idle is not affevted by pressing the brake pedal.
The cable doesn't seem to get blocked in something.
By blocking the pinhole, the idle seems to be affected.
What is that pinhole for?

 

[Brendan W]

The idle is not affevted by pressing the brake pedal.
The cable doesn't seem to get blocked in something.
By blocking the pinhole, the idle seems to be affected.
What is that pinhole for?

I forget exactly but it's supposed to change the idle.
More headscratching.

 

[crash25]

Maybe the coolant temperature sensor?

 

[Brendan W]

Disconnecting the coolant sensor will put the idle speed up a little but you should see a red temperature warning and the yellow triangle as well.

 

[crash25]

Was thinking of the coolant temp sensor because it does so only when the engine is warm.
Also, the intake manifold was changed in january, with new gaskets. It didn't do any of the revving until June...
Also, it's interesting the fact that whenever I take off the filter and put it back, it doesn't revv for a few days, then slowly gets back on its own.

 

[Brendan W]

Was thinking of the coolant temp sensor because it does so only when the engine is warm.
Also, the intake manifold was changed in january, with new gaskets. It didn't do any of the revving until June...
Also, it's interesting the fact that whenever I take off the filter and put it back, it doesn't revv for a few days, then slowly gets back on its own.

Have you checked the inlet manifold nuts. The bottom pair in the middle are tricky to get at, especially the one on the battery side and sometimes it gets forgotten during a tool change.

 

[crash25]

No, I haven't. It's quite narrow in there

 

[crash25]

Any help, please?

 

[Brendan W]

You can get at them with a ratchet and extension from behind and underneath the ecu plugs. You'll probably find it easier with a wobble joint at the socket.

 

[crash25]

Gonna try that. Also, I think I'll change the plug leads, because I haven't changed them in 3 years now.
Gonna tighten the throttle body as well and see if that improves anything.


Also, I might change the throttle cable, as I think it's the original one. Is there a tutorial maybe on this forum? I haven't seen one.

 

[s and b]

i had a panda and sold it ,it came back as intermittent over revving as yours does,this too had a brand spanky new throttle body on from poland,after lots of attempts to stop the fault including one long drive with mes connected i concluded the throttle body was junk,found an old one in my stores fitted it car perfect

 

[puntoFix]

Mine stays high when I rev and take foot off, then slowly comes down. I have decided it is the idle valve going bad. I ordered a new one, will report back if it fixes it.

You may have a bad one also which is affected by heat as it can change resistance as it hotter.

Air filter making it better may point to throttle cable as it sits on the filter housing on the battery side and may be coming off and causing some sort of issue.

 

[puntoFix]

I changed my Idle control valve at the weekend and it fixed the issue.

A good test. Is to remove yours use a jubilee clip around it and twist a flat head screw driver against the Clip and throttle body. Mine was well stuck but it will come out.

When you get it out turn the ignition to MAR, on but not running and the pintle should extend fully and return to near closed. Mine was not doing that but the new one did.

If your careful you can easily put yours back in if it is not faulty.

 

[crash25]

Hello,


I changed the whole throtle body with a new one in July. It started doing again about 2 weeks after I changed it.
It doesn't do it when it's cold, only when the engine got warm, and only sometimes. When it's warm, it also doesn't go back down to normal idle rpm from the first time, but it kinda slews down from 1000rpm slowly to ~750.



I think I'[m gonna swap the throttle body with one of my older ones and see what that does...

 

[puntoFix]

Unless its a new throttle body with new sensors ie throttle position and Idle control valve you could still have an issue.

Maybe check the wiring on the throttle sensor and idle control back to the ecu.

There is a test you can do on idle valve wires using a test light to check them.



Heat can play a big part in electrical sensors and step motors, resistance is greatly affected by it.

the slow reduce in revs does sound very much idle control related. it basically opens and closes based on the ecu input.

if it does not work properly ie is slow in responding then the ecu will tell the injectors to use the specific amount of fuel to keep the 14.7:1 ratio of fuel air.

The lambda sensor detects a lean due to the idle not closing fast thus ecu keeps fuel adding, as the idle valve closes less fuel is added.

if you do the test I said about taking it out and looking how it reacts cold and after been heated you will know if it is the idle valve.

Start simple, idle valve test, throttle position reading on obd scanner, electrical short/ ground issue on idle or throttle wires.

Also check lambda sensor before Cat just to make sure its working, voltage on obd scanner or multi-meter signal wire should go positive when you introduce carb cleaner to air intake, listen to revs go up car has to be in closed loop (up to temp) probably.