MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGF Technical - Throttle body- ?Sticking or is normal?

Hi there, got my F in july 02, massively addicted! Already a follower of Rob and Dieter (yer kinda famous guys - no autograph request though!)

Anyways have noticed that as I am starting to depress the accelerator (or if i turn the accel cable attachment on the throttle body) there is a step of resistance then the motion continues smoothly.

Previous owner had the accel cable replaced.

Thoughts:

1. Is this normal?
2. Have read about previous accel cable issues, but since there is the same step when manually turning throttle body attachment, is there a prob with the body mechanism?

(plus I kinda hope there is a prob, cause I just need an excuse to buy the Mike Satur upgrade - unless midgey bell thinks differently)
R H Greig

Its a 1999 MGF VVC, with K&N57i (although I know thats not showing off - but hey it does sound sweet)
R H Greig

Plastic or aluminium TB? FWIW, if you have a K&N a Trophy Alloy TB will help get the most of it, and if you have a reason to replace it anyway...
Leigh

>the same step when manually turning throttle body attachment

Looking at the whole design,
- could be the sensor at the rear /bolt off and try whether it sticks still
- could be a broken or blocked worm spring (spelling?)

You may also try to look into the body from entry side when you dismantle the airfilter. Lokk at the plastic flap while torning the assy. The flap is bolted on with brass scews (almost). If they look damaged at the rear thread side, then may be anyone had dismantled the body and wrong re-assembled.
A bent flap shaft could be possible also. (cheap weak brass shaft)

Worth to upgrade with an ally body :)

HTH
Dieter
Dieter K.

Make sure the K&N clip is not overtightened on the throttle body as this tends to distort the plastic and make the throttle stick.

Spyros
Spyros Papageorghiou

Well, thanks Rob ;o) LOL

In answer to your question, no, that isn't normal. The throttle operation should be smooth and of even resistance throughout the arc of movement.

Suspicious that the previous owner had replaced the throttle cable.

There are 'issues' with the plastic throttle body, as you probably are well aware of, and Dieter has already summarised.

But in my experience, problems with the throttle body usually manefest themselves as a raised idle speed and some degree of 'stickiness' (holding rpm after release of the throttle).

This odd change of resistance suggests, to me at least, that the cable is the first thing to check out: are there any kinks causing it to stick?

Regarding giving Mike a call for the TB upgrade? Who am I to argue with that idea? ;o) LOL BUT I don't think that it will resolve the problem here...
Rob Bell

>But in my experience, problems with the throttle body usually manefest themselves as a raised idle speed and some degree of 'stickiness' (holding rpm after release of the throttle)<

If i rev mine to about 5k revs or higher, the revs seem to take a long while to drop back down, is this what you mean Rob? (Bell). I just thought this was normal as it doesnt seem to affect anything when the car is in gear and moving.
G.C

I think what you are describing is the fly-wheel effect of the engine - slow, but progressive loss of engine speed, GC. Nowt to worry about as you say :o)
Rob Bell

Thats okay then,Cheers Rob.
G.C

Thanks.
Now that you mention it Rob, the revs do stay up when releasing the accel during gear changing.
(have to quickly depress and release accel to over come it)

Spyros: the K&N attachment isn't too tight, had the fear when fitting to the plastic body that the Rover engineering aint what British quality use to be

Dieter: will try yer idea to check the bolts etc first (when the rain stops, does the rain ever stop?)

I have the feeling i have an excuse to shop! ;->

Rob Greig

Just to echo what has been said:

I had a problem with my (old) plastic TB sticking, this was finally traced to the two retaining screws for the throttle position sensor (potentiometer) being over tightened. Basically, they were projecting too far out the back of the sensor and were fouling the return spring on the back of the TB. To test to see if this is happening, If the revs are staying high when idling, manually close the butterfly on the TB (by operating the throttle cable cam). If it clicks and then the revs drop then this is the most likely cause IMO. The potentiometer is situated on the far side of the TB making access tricky, you are likely to need to remove the engine bay cover under the parcel shelf lining to get access to this item. slacken off the two screws a turn to cure.

Another problem, which is also quite likely is that the throttle cable isn't seated properly in the throttle cable cam. This is especially likely if the throttle cable has been replaced. Visually inspect and adjust if necessary.

Lastly, when replacing the throttle cable it is very easy to kink it, when i did mine, despite being careful i still managed to produce two of them. In my case the result was a fairly stiff feeling throttle pedal and i suspect that i have shortened the lifespan of the cable. To this end i carry a spare - it's a known problem on my car so in the best boy scout tradition of "being prepared"... ;-) Anyway, back to the point, if the cable is kinked or poorly routed then i suppose it is possible that it could be 'snagging' and this may produce the symptoms you describe. A visual inspection of the cable should suffice, alternatively, you could diconnect the cable from the TB butterfly cam and manually pull the cable, feeling for any snags. the cable (obviously) is attached to the throttle pedal, it then follows the edge of the footwell, along the side cill (where it meets the bonnet release cable), through the metal cill butress, up the engine compartment wall, under the T bar and then onto the parcel shelf where it dissapears into the engine bay through a grommet. Inside the engine bay it wraps around the inlet plenum to the TB butterfly cam.

HTH

SF
Scarlet Fever

Anyone had probs with TF at low speed in traffic i.e between 900-1500revs,1st.2nd gear.Mine drives like a clog and a pump!Also, on light trailing throttle as revs drop to 1500ish,throttle seems to snap shut.Have had fitted E.C.U.,Throttle body and potentetithingyometer, all to no avail.M.G. Rep describes condition as "ACCEPTABLE"!! This has only been going on for 6 months.Any comments anybody.P.S. PIPERCROSS Panel filter from Mike Satur is top cheap easy tweak for T.F. REGARDS.
bridge

This thread was discussed between 21/01/2003 and 24/01/2003

MG MGF Technical index

This thread is from the archive. The Live MG MGF Technical BBS is active now.