Idle speed increased

[Shellie]

Does anyone have suggestions as to why my P reg MGF's idle speed has increased?
It is now ticking over at 1300 rpm whereas normally it is at about 800 rpm.
I have tried simply blipping the accelerator pedal but the speed settles consistently on 1300 rpm.
This has only just started. Is it likely to get worse? Apart from this, the power and performance seem normal in every respect.
Thanks for any replies,
Shellie.

[bgunn]

Quite likely that the plastic throttle body is warped - this can occur on it's own, or if the clip that holds the inlet hose on is replaced for a jubilee clip, which is then tightened up too much.

Or there's another fault causing the idle speed to be raised, best bet is to get a fault code reader on the engine management and have a quick look..

[Matt Parker]

Most likely you will have aplastic 48mm throttle body, these are prone for distortion from heat, oil and over tightening of the airfeed pipe clip(jubily type) and making the throttle valve stick(hard notchy feel from pedal) or by not allowing the valve to fully close when returned to the stop for idle allowing extra air to be drawn in raising the rpm. First thing to do is check and make sure that the inside of the throttle body is clean of oil, hold open the throttle and use some choke/carb throttle cleaner anda rag. make sure that the airfeed clip is not over tight, just tight enough so you cant pull the pipe off the throttle body. Ideally you want to fit an alloy throttle body on, 48mm or 52mm.

Before the above you could try resetting the throttle potentiometer (sensor to tell the ECU what position the throttle valve is at) you do this by switching the ignition on to position 2 (dash lights on) and then apply full throttle on and off a minimum of 8 times, this will allow the ECU to know exactly what position the throttle valve is at just incase it has become out of sync.

Failing those, you may have an air leak somewhere on/around the throttle body and inlet manifold and connectins pipes. With the engine running listen around your engine for any hissing noise indicating air being drawn(sucked) in, if you are unsure of this you could then try lightly sprayed wd40 or carb throttle cleaner around the joins of the inlet manifold and vacuum pipes, if the tone of the engine revs changes then it will indicate you may have a leak in that area.

[Rob Bell]

I agree with Matt and Brian - a warped plastic throttle body is a likely cause of the uneven idle - but replacement is not cheap, as alloy throttle bodies do command a premium for the obvious reasons.

Before commiting oneself to that line, I would check to see whether there is a problem with the water temperature sensor that the engine management uses coolant temperature. It is separate to the one used by the dashboard gauge, so this often gives no clue.

The easy way to see whether the temperature sensor is working or not is to see whether the radiator cooling fan comes on as the engine temperature increases. Warm the engine by going for a drive first, and then, when you get home, leave the car to idle. The engine bay fan may come on, but ignore that. See whether the rad fan switches on (audible from the front of the car). If not, and the engine temperature on dash starts to rise above half way, you have your answer.

Replacement sensor around 10 quid. Sure beats around 100 quid for a new throttle body!

Few other causes of a fast idle are listed here: http://mgf.ultimatemg.com/group2/Thrott ... tm#problem

[Shellie]

Thanks Matt!
Resetting the potentiometer did the trick and it now works fine with a nice 700 - 800rpm tick-over! Come to think of it, I may have inadvertently started the car with pert throttle one day, as my other car is a Mini and likes that. Maybe that caused the ecu to become confused?

Thanks again!

Shellie

[Matt Parker]

Thats good

usual reason for going out of sync with the ecu is down to being disconnected at some point, head gasket replacement? or the connection plug may be slightly loose. Other than that only way it would have gone out of range is due to it saying to you that it may be on the way out and want replacing in the not too distant future. If you start to get the problem occur more often then you know what your have to do, replace the sensor, or better the complete throttle. Alloy 48mm throttle bodies can be bought from as little as £1 off ebay if you keep an eye on the market

[Shellie]

Hmm, I did go over a major pot-hole that may have jolted a connector. I was quite a bang! We will see, but thanks very much!
Shellie

[Shellie]

Sorry, IT was quite a bang!

[Rob Bell]

Thanks Matt!
Resetting the potentiometer did the trick and it now works fine with a nice 700 - 800rpm tick-over! Come to think of it, I may have inadvertently started the car with pert throttle one day, as my other car is a Mini and likes that. Maybe that caused the ecu to become confused?

Thanks again!

Shellie

Excellent result!