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MG MGF Technical - GM Throttle Body, R U Out there Dieter?

This is a call for help from Dieter especially, but anyone who has done the GM throttle body mod, please chip in.

I followed your instructions closely Dieter, and there is now a GM Throttle attached to my car. I adjusted the stepper motor and took up any slack in the accelerator cable.

She is however not a happy puppy.
When fired up, she ticks over at around 2000rpm!

I took her out for a tentative test drive. Initially she revved very high, and the revs took a long time to drop, however, after a few km, she was warm enough to open up a bit, to around 4500 rpm and following this, the revs kept trying to drop to zero. Opening up to far too fast resulted in the power cutting out, rather as if I had gone too far into the red.

She proved impossible to control at low revs, I stalled her getting into my parking place, and she would not re-start without a tickle on the accelerator.

The only point I was a little concerned about in the instructions was your line stating "measure the resistance between pins 1 and 2, on the old throttle, and make sure that this is the same when the sensor is placed on the new throttle. This should be around 760 Ohm." I got only 675 Ohm, and duplicated this faithfully on the GM body, (a boring job if ever there was one). This resistance was terrifically sensitive, even responding to the tightness of the retaining screws.

Is this resistance reading too low? Between which two pins exactly should it be measured? I measured between the centre and the right hand pin, (looking down on the pins, with the sensor nearest to me).

Have I completely fouled up? Habe ich alles versauert? Is there an answer to my cry? Will my pride and joy recover?

Viele Grusse

J. A. Farrington

Hi Jim,

did you reset the TPS ?
Ignition on, don't turn over to start, key the accelerator 5 times, ignition out. Then restart the engine. This should adapt the lower value of TPS resistance to the ECU.

I think 675 Ohms may be a bit low, but would be OK.
I hope you didn't forget to put a paper gasket between TB and plastic manifold to get it sealed from 'wrong' air.
Email if it doesn't work for you. >> mgf at mgcc dot de.

Dieter K.

Hi Jim,
as I was doing the GM throttle-body conversion I initially forgot to swap around the 2 outer cables to the throttle-pot. This ment that the potentiometer was "going the wrong way" and gave a very funny driving experience ;O).Was corrected after a very short drive and has been all OK since then.
Are You sure the potentiometer arm is going the same way as on the old plastic body ?? / Carl.
Carl Blom

Hi Carl
Thanks for the advice, I did swap the wires round going into the sensor as advised, but I had to cut the two outer wires further down the cable and re-connect them, as the pins could not be released from the plug.
Good point though, my initial thought was that there was a problem with these connections.


J. A. Farrington

And in addition to what Dieter wrote; Any unwanted air leaking into the mainfold will also give similare problem...Sure all openings for the original GM magnitude of vacuum-hooses etc. are well sealed ? As for the releasing of the inserts in the potentiometer plug - yes,it is a pain in the ... but a good needle will usually help. And after managing how to do it the next one is easy !

/ Carl.
Carl Blom

Hi All

I have done all the suggested things regarding the TPS and checking for leaks, and she is still ticking over at 1600 rpm. Can't believe that there are any air leaks, the gasket now looks good and tight. I was wondering if the fact that I bought a 19mm internal diameter breather hose for the new GM throttle body might be causing her to breath too freely on tick over. Is this possible? It certainly seems to be a lot larger than the original. She breaths fairly freely anyway through a K&N filter.

I seem to be running out of ideas. Suggestions anyone?


J. A. Farrington

Hi All

Just tried kinking the large breather hose while she was ticking over and the revs fell nicely to 800 rpm. Not sure whether my solution is a bit simplistic though, could I be missing something more fundamental?

All the best

J. A. Farrington


see email as well.
Did you reset the TPS ?

Pinching the mentioned hose overcomes/disturbes the idle regulation of the IACV (idle air control valve) better known as stepper motor). So it's OK if idle drops if the hose gets pinched. The engine will stall if you kink it completely.

Another idea. Could be a vacuum related leak.
Is the vaccuum pipe proper mounted to the right of the TB at the inlet manifold ?

PS. still the cr*p connectors in mind
Dieter K.

Use some WD40 spray to detect whether there is a gasket/ pipework leak. Vacuum leaks can cause all sorts of odd running symptoms.
Rob Bell

This thread was discussed between 22/08/2004 and 25/08/2004

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