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MG MGF Technical - MGF fast idle running problems

Hi all,
Ive just got my F back after a having a recon head fitted (Which has taken MONTHS!!!!), but its idling at about 1200-1500, even when hot.
This has now been joined with a miss fire on excelleration and at low engine speeds.
I was hoping that resetting the TPS would fix it, (can anyone remember the sequence?)
I know it could be electrical, ie damaged spark leads when the plugs flew out, but i get the felling that its over fueling, ie running rich, is that possible???
Im at a loss and carnt afford to do the scattergun approch to the problem this time.
Thanks in advance,
John
J E Reed

It could be the throttle cable has insufficient play - the inner should be slack and have a little play when at rest. My F had similar issues when I first had it with 1100rpm idle speed and jerky response at low throttle. Dr Dave had a looksee and introduced some slack - problem solved.

The TPS reset method is with ignition on, depress throttle fully five times in 20 seconds, and switch off for 10 seconds.

The above can be found on Rob Bells site, with all sorts of info about throttle bodies and things to checkout.
http://www.mgf.ultimatemg.com/group2/Throttle_body/index.htm

Jeff
J Lennon

Fast idle & rich running I'd suspect to the the ECU not getting a temperature reading, and thus applying cold-running mode, i.e. full choke. The ECU gets its feed from the brown sensor which is right next to the blue/black sensor (which feeds the dashboard gauge) on a casting at the end of the cylinder head. Was the sensor swapped from your old head, or did the recon head come with one already fitted? Either way, it could just be a feeble connection, which a clean up of the contacts with abrasive paper and a sluice with electrical contact spray is likely to resolve, or a failed sensor.

Easy way to test is to pull that connector off while the engine is running at normal operating temperature. If there's no change in the idle speed, the ECU wasn't getting a feed from the sensor.
bandit

Thanks Bandit and Mr Lennon, off to see if its the sensor,
I wonder if this was the original problem that blew the plugs out?
Many Thanks
John
J E Reed

Hi all,
after changing the ecu temp sensor and plugs and leads
plus a service and ecu and throttle cable check,
Their is absolutley no change whatsoever!!!
infact, the rev limiter now kicks in at 5500rpm!
my garage thinks the janspeed manifold, ITG and 52mm TB are to blame.
Had to explane that they are common mods and ive never heard of anyone else having these problems!
Bum Bum and Bum.
can anyone surgest a MGF/TF or K series Guru near newbury please?
J E Reed

No way is it the manifold, but the TPS could be out of spec, and inlet manifold leaks can cause problems.

Other areas to look at include the IACV - worth looking at and cleaning.

I am also wondering about the crank position sensor if the rev limiter seems to be cutting in early?
Rob Bell

Agreed, if those mods worked well on the previous head then absolutely no reason to suspect they're the cause now. Has the problem existed directly from having the replacement head fitted, or did it run ok for a while and then started misbehaving?

I don't think you need a guru, or not yet at least. Just to clarify, was the coolant sensor changed because there was no response from the engine when it was disconnected? If there's no change when a new sensor is fitted, clearly the problem wasn't the sensor, so wiring needs to be tested for continuity. Wires that have sat in one position for many years of heast cycling can fracture when disturbed, and hitherto faultless connectors that have been left dangling for just a few days can oxidise & corrode enough to become unreliable. Eliminate all the simple & nil-cost possibilities first before investing in any new bits.
bandit

Thanks Bandit,
but i have to admit i dont know what to do, or where to start!
the problem was there after the mods and before the recon head, just not as bad.
The sensor was changed because it was alot of hastle just to check it worked and if it was dodgy i needed to have one to hand anyway,it made sence just to change it if you get me.
whats the IACV?
J E Reed

The IACV (Idle Air Control Valve) is bolted to the inlet plenum, and can be affected by dirt/oil. There's a very primitive test of whether it's working ok, which is to squeeze the inlet air duct closed with the engine running - if the idle drops, the IACV isn't opening to allow 'top-up' air in. Either way, I'd recommend removing it and cleaning it thoroughly with carb cleaner. You never know, maybe ITG were a bit generous with the oiling of the filter... The wiring to the IACV can be troublesome too, check there are no tight radius bends in the cables. And get a can of electrical contact spray (Maplins, Toolstation etc), disconnect every single sensor connection you can find and sluice both sides generously, drain out & re-connect. That simple method has cured many a problem. The crank sensor is mounted close to the starter motor, pointing at the flywheel.

It's possible that if none of the above has any effect the next step would be a TestBook diagnostic, which would show whether the sensor inputs are correct. It's not a 100% guarantee that any problem will have an error code logged, but it will show what the ECU is seeing.
bandit

This thread was discussed between 21/02/2010 and 12/03/2010

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