[MG TF]

I got a MG TF 160, 2003. It battle to idle when cold and when hot it cuts when you switch the aircon on. Where can I look?? Part from this, a lovely car. Spares a huge problem in South Africa. Regards

 

[Julian Foulger]

It could be a range of things but it should idle at circa 875rpm when hot. I have aircon which when I switch on, the ECU increases the idling revs by circa 100rpm. I would look at your IACV (see recent post on this) first.

Regarding spare parts, same situation here. All my spare parts have to be shipped from Rimmers in the UK.

 

[nocturneblue]

Note that there are two recent posts on the IACV, one is just a follow up. Also, one of them mentions the idle reset procedure which is worth a go I suppose as it's easy to do. I've never done it but it involves fully depressing the accelerator pedal five times within 30 secs I believe, with the ignition key set to the correct position but you'll have to search this forum for the correct procedure.

 

[nocturneblue]

Note that there are two recent posts on the IACV, one is just a follow up. Also, one of them mentions the idle reset procedure which is worth a go I suppose as it's easy to do. I've never done it but it involves fully depressing the accelerator pedal five times within 30 secs I believe, with the ignition key set to the correct position but you'll have to search this forum for the correct procedure.

EDIT: I believe you start the car, turn it off, set the key to ignition position II, then depress the accelerator pedal fully five times (within 30 secs?). Even then, the thread I saw on this procedure said it takes the car 300 miles to 'relearn' things (I presume the ECU tunes the idle with both short term and long term control parameters).
NB: The forum search function is buried inside those three dots at top right of the screen.

 

[Julian Foulger]

Regarding the so-called reset, what this does is reset the throttle position sensor (ie TPS ). It is only one of many potential solutions) The TPS may still not be right if 1. It is faulty and 2. The physical butterfly valve is not open at an actual 4 degrees when the engine is off, especially if the throttle adjuster screw has been played with (this adjusts the extent the valve is open [number of degrees in the vertical] at any point when the accelerator is pressed.). You may get lucky but the truth is you are adjusting one variable (TPS) whereas there are two (TPS and throttle adjuster screw). In addition, there are a number of physical components that be wrong - TPS, IACV, vacuum pipe, accelerator cable....).

In my case, I ended up replacing many sensors (including IACV and TPS but also Cam and MAP sensors)) but the key cause of the problem was that the throttle adjuster screw was not correctly set by the factory (I had replaced the 48mm throttle body with a new 52mm one and the idling was never right from square one).

I regularly recommend PScan (I am not on commission!) because it outputs many variables (including TPS position by degrees and number of steps per IACV), both key variables in getting the idling 1. Idling at circa 1200rpm at cold and 2. Closer to or on 875rpm at hot idle (with aircon off). 3. From speed to stop, ensuring that the rpm drops steadily down to 875 rpm at standstill.

Pscan would have saved me a lot of wasted time, endless frustration and saved me much money if I had had it in the first place. I do not have access to Testbook so for me Pscan is the only solution.

 

[MG TF]

Thank you so much for the advice. I appreciate it.