High Idle

[oddjobsd]

Hi all, newbie to forums, and had an mgf for about 8 months after writing off the other halves car, so it's technically hers, but it's me who funds it, and works on it etc, so going to claim it as mine.

unfortunately i have become confuzzled, over the last couple of weekends i have changed the track rod ends, as they were an advisory on the MOT, and fitted braided brake lines, bled the brakes, and the brake lights were stuck on permanently, so in the rain there i am, head in footwell, resetting the brake light switch (ended up taking out the seat to accommodate the width of my shoulders in the footwell), brake lights now work on demand with the pedal, happy days.

Start the car and the idle speed has shot up to about 1500rpm, when about 15 minutes before it sat happily just below 1000rpm. is it likely that i have broken something, or would you expect this to happen??? I did disconnect the battery to remove the seat, could this have buggered something up??

its a 1996 vvc model, if this helps.

thanks in advance,
Stuart

[bigmac]

surprisingly--my f has just sailed through the mot--with no advisories---but i know my brakes flicker sometimes when i'm driving it. ive read up on here how to fix the switch--even bought a new switch some time back--but it dont look right to me.

just waiting for a nice day now--so i can grovel in the dirt and dislocate my shoulder attempting to do the job.

or do i chicken out and let a garage do it?

sorry if i'm a bit off topic.

[Mykel]

Hi and welcome Stuart,

I'm sure you have checked all obvious things around the footwell area, like a floor mat getting engaged in the pedal mechanism aso asf. If the high idle persists, I'd try and reset the throttle position sensor. This is how it's done: Turn the ignition switch to pos 2 but don't start the engine. Wait a couple of seconds. Next gently but firmly press the throttle pedal to the floor five times, releasing it completely inbetween. Switch the ignition off first, then start the engine as usual. Revs should now settle at 850, if the engine is warmed up.

hth
Mykel


EDIT: Be very careful claiming the better half's MG as your own, you might end up in big trouble :
viewtopic.php?f=7&t=14573

[oddjobsd]

Mykel,

worked spot on, started it up this morning, still on high idle, reset the sensor, and is purring like a dream now . With regards claiming it as my own. I think i'm safe, she recently suggested swapping it for something more sensible as we will be moving to Scotland in a couple of months. she thinks it will be difficult to use when it all goes white. my solution was to run 3 cars, which i think is acceptable, and i'll use the F for the less white months of the year.

Thanks for the help,
Stuart

[Mykel]

Glad I could help, Stuart. The MGF really is quite good in the winter, weight distribution is optimal, good punch on the drivewheels when going uphill. And they stand up to rust better than you'd expect, some regular TLC provided. The only essential thing is putting a set of decent winter tyres on when required. Also, incorrect ride height setting and wheel alignment issues will have more impact when the roads are slippery.

I have a set of cheapo 6-spoke 15" alloys (can be found on ebay for 50 quid) and had a set of Kumho I'ZEN KW23 fitted. In proper summer sizes by ty way (185 front, 205 rear). It was the third winter now since I bought the little princess, and we never had an issue with the white stuff.

So there really is no need to get a third car ... except if you are a wacko like me who runs 2 MGs now, and can't really stay away from web sites like gumtree, trovit, and the big ole bay of "E" ... ah, the temptation!

[Ian]

My first post on here so here goes !

The high idle speed on the MGF is a very common problem, you can google it and find hundreds of owners trying to track down the problem when it occurs. I was one of those owners and for about a month it was my mission to find out what was causing it on my MGF. If I can share my experience it might help if you are chasing your tail on this one !. In my case it was the Throttle Position Sensor which was intermittently faulty (sometimes it recorded the right voltage to the MEMS other times it wouldn't and this caused the MEMS to give up and default to a preset state - hence high revs, slow return to 1500 RPM when using the throttle. Having gone through all the obvious like a stuck throttle (mine was an alloy throttle body and it was shut when then problem occurred), cleaning the idle control valve - if you haven't done that I would its worth it, I was still stuck with the problem and really scratching my head. I kept a spare key in the car to open the boot to catch the engine "at it" when the idle revs were high !. My recommended order of checking things are:
1. Mechanical issue - i.e throttle valve not shutting properly (this happens on the plastic ones when hot ?) I guess trying to close it with your hand will prove this one.
2. Air Leak - check hoses to idle control valve and anything else where air could leak in past the throttle valve.
3.Idle control valve, clean it and check the 5 connections to it on the connector (mine were loose which didn't help). If you can take the idle spindle out - see photo attached. You need to connect 12 volts to the centre upper pin and dab earth to each of the "poles" windings. Watch out though - the inner pin fires out when it reaches the end of the thread ! To replace it, line it up in the motor end and reverse the sequence of earthing the winding poles, keeping your finger with light pressure on the end of the spindle to help it go back it via the motor thread turning. for reference: http://www.mgfcar.de/sensor/

Idle control valve thread - this partially cleaned up.

4. Black connector on the MEMS ECU, this inputs / outputs the sensors from the engine, check its OK and it making a good secure connection to the multipin connector on the ECU, its delicate so handle carefully. Don't attempt to bend any pins on the MEMS unit, the plug will never fit after !
Check The Security Of The Engine To ECU Wiring Loom !. I've just found one cable tie that was missing allowing the loom to "swing" a bit. This then transposed into a bit of leverage / movement on the Red and Black ECU connectors. Small variations in the quality of connections whilst it moved about started to cause havoc !. The cable ties holding the loom to bulkhead and also the loom to support bracket (next to Multifunction Relay Unit) MUST be present and secure !. Ghosts in the machine otherwise !. See replaced cable tie in the attached photo, I gave it two ties, white and a back up small red one !

Replaced cable tie(s). With it missing all sorts of strange things happen !

5. The ECU coolant temp sensor - the brown one ! - connections to it and whether it is in spec - http://www.mgfcar.de/sensor/
6. Throttle Position Sensor - worn out on the nearly closed throttle position ? ( fault on mine was this ). again check with it in the car - specs for it: http://www.mgfcar.de/sensor/. Also check the voltage off the TPS at throttle STOP. Mine wasn't happy below 0.7 Volts and and the engine occasionally defaulted back to high idle again ( I guess the MEMS unit is off its "mappped" memory). The regulated voltage to the TPS is 5 volts, with as bit of ohms law the resistance of the sampled TPS was approx 650 Ohms. Easy to check with the connection off and engine off.
7. On the VVC engine it might be the cam position sensor - rare, but according to the workshop manual it will default the MEMS into a high idle state if it loses this sensor input.

I guess my long search helped me understand what was going on with the sensors etc, the MEMS will be looking for correct engine temperature, engine running speed, throttle postion, air temperature and air mass. All those inputs provides the right position for the idle control valve - ignition timing and the correct fueling for the injectors.

Best Regards