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MG MGF Technical - Sticking Revs (again!) - Not TB

I know this subject has been done to death, but I am at work and so cannot log in to trawl the archives, and have to go on a long journey after work, so thought I would try and fix the car today!
Over the last week or so the revs on my 97 VVC occasionally stick at around 1300 or 1400 rpm. It happens mainly when the car is cold. I can reset the stepper motor and it returns to normal idle, but often sticks again afetr a short while.
I have already fitted a TTB - (which cured the previous problem of the throttle sticking with the engine hot!). So what causes the sticky idle with a cold engine, and how do I check this?
Jason H
Jason H

Jaso,
I saw 'mike' once dismantle and clean the stepper motor itself at Erik's car.
May be this helps.

On the other hand I would look for the oxygen sensor.
Dieter K.

Don't forget to check the idle air controller, it sometimes sticks and can be cleaned with carby cleaner.
Grant Vowles


If not the idle valve it could be a problem with the TPS?

Throttle Position Sensor (TPS) may have a bad connections internally or externally?

If you can, while the engine is running connect, disconnect and wiggle (highly technical that last one! Make sure you're qualified. ;-) the connector to see if revs change.

I replaced mine to try and fix this problem only to find that it was a broken cable/connector.

The wire/connector reqiures a new loom from Rover - which is plain stupid. Instead I replaced the connector with one from a scrapped Peugeot as they are identical.

Hope this helps.

Paul.
Paul Nothard

Thanks guys,
But how do I check the idle air controller? and if it is not that then where is the stepper motor and how do I check it?
Jason H
Jason H

On a more depressing note, my 96 1.8i F had this - we replaced the throttle cable, throttle body, Temp sensor. In the end, we concluded (correctly) that the computer was sick. One new computer later and the car works again.

The work was done by a rover specialist, rather than an MG Rover dealer

Hope it isn't your computer
M
Mark

The IACV can indeed block up. There's more on this in the Elise Technical archives. I understand that it is a question of partially stripping the TB and cleaning things up - possibly not something that can be done if you're still at work?

If the throttle position sensor, try resetting it, using the usual throttle depression 3 times with ignition on 'II' and switch off procedure, and see how that helps, Jason.

Rob Bell

I too hope it is not my ECU - had a new one of those last year for a different fault!
Rob, as my TB is quite new - m,onths rather than years old - could it really be blocked already? Yes resetting the idle position with the throttle pressed a few times does cure the problem temporarily!
Jason H
Jason H

Seems unlikely doesn't it Jason? Might be worth popping the airfilter and having a look inside the TB using a mirror. If the inside of the TB is spotlessly clean, it'd make a blocked IACV even more unlikely.

Might be worth just checking that all the pipes are properly secure, and not leaking air (including the 'O' ring between the TB and the inlet plenum).

Odd that you can temporarily 'reset' the potentometer. Perhaps there is an electrical problem here, as Paul suggests? Remove the plug, check and clean all contacts, and see if that helps. Thereafter, you might need to look at the resistances to determine whether there is a problem with the loom or the rheostat itself.

Wouldn't a potentimeter fault show up on Testbook?
Rob Bell

This thread was discussed between 03/02/2003 and 05/02/2003

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