Sticky Throttle

tanick · Post by **tanick** » Wed Oct 18, 2006 8:54 am

Thanks to Alan.UK, my car is now sporting a nice new pair of bellcrank bushes however the throttle still isn't right.

When I take the car our of gear the revs drop to 2,000 then sit there for a while before dropping back to idle. Fine when driving but embarrasing at traffic lights. If I hook my foot round the gas pedal I can physically pull it back and drop the revs. I've been through the whole system (several times). From the bellcrank to the engine is totally free. There's a bit of resistance on the rods in the tunnel but there's nothing really for them to get caught on in there and all looks free when I look through the various inspection holes The pedal cluster is totally re-furbished.

The only thing pulling the revs back to idle (so it seems to me) is the spring wrapped round the MFI crossbar. I've put another turn on this to tighten it. Should there be a spring anywhere else in the system? It seems there's nothing to pull the linkage back when I ease off.

Luke · Post by **Luke** » Wed Oct 18, 2006 9:06 am

2 suggestions:

1) it's not catching/rubbing on a spark plug wire is it?

2) Could be the pedal assembly, take the floor board out and check whether the rod that connects the rocker to the pedal (or the rocker itself) is rubbing on the chassis. I had a small burr on the chassis that was catching the rod at about the 1/3 open postion, a quick carress with a rasp file and its been fine ever since.

tanick · Post by **tanick** » Wed Oct 18, 2006 8:30 pm

Hi Luke, how are you doing.

1. No I thought it might be the linkage catching on the vacuum pipe to the o/s throttle bodies.

2. I'll try going for a drive without carpets. I've narrowed it down tot eh linkage in the tunnel or the accelerator pedal itself. Is this sprung to pull back? If I can't get it to work I'll put a spring on the bell crank!

No matter what I do I can't get the linkage to release enough on its own to click the over-run solenoid.

Maybe the whole thing just needs adjusting.

2.4TE · Post by **2.4TE** » Thu Oct 19, 2006 12:41 pm

I've had a similar problem that I've cured temporaily with a couple of return springs. My problem is that the damper on the throttle rod rubs on the transmission mount. Could this be your problem? I don't know the correct way to cure it yet.

tanick · Post by **tanick** » Thu Oct 19, 2006 5:33 pm

Damper? Which bit is that?

gav p · Post by **gav p** » Fri Oct 20, 2006 11:32 am

Nick, the throttle pedal itself has a spring in it, such that it should pull itself up when you remove your foot, and hopefully contribute to closing the throttle. This is moulded inside the rubber of the pedal; in the past I've managed to restore some springiness by squirting WD40 into the pedal hinge area (under the pedal rubber, with pedal removed).

From memory, my MFI has at least 7 other original springs, one on each butterfly and one at the MFI pump crank.

BTW the damper referred to by 2.4TE is the rubberised throttle link forward of the bellcrank. If this is catching on something then it could mean the throttle rod in the tunnel is not correctly routed through its bushings, but is floating unsecured around in the tunnel.

Cheers...

stevieboy · Post by **stevieboy** » Fri Oct 20, 2006 11:45 am

Have same problem with mine, foot off and drops to 2000 revs unless you pull the pedal up a bit, by hand or foot. Doesn,t make for easy driving.

Have gone through it all from front to back, lubricating everything in sight and making sure nothing is catching or rubbing anywhere. It wasn,t

Still happened checked the whole of the pedal assembly,including the brake and clutch, everything ok as its reasonably new.

I,m now certain its the throttle pedal its self.
Glad to see Gav has reminded me that there is a spring mounted into the rubber pedal, thats my next port of call..

I,m not with the car at moment, so Gav is the spring hidden under the rubber, is it easy to get at and can you replace the return spring on its own or do you have to buy the whole pedal.

2.4TE · Post by **2.4TE** » Fri Oct 20, 2006 12:22 pm

Gavin,

Can you access the bushings that the throttle rod runs through in the tunnel? If so, how?! Thanks!

gav p · Post by **gav p** » Fri Oct 20, 2006 2:13 pm

Stevie - The spring is an integral part of the pedal hinge, with the rubber moulded over it, so you have to replace the whole thing at once. However, on my old 912 it was still possible to squirt oil in there which got it working again.

Re the bushings, I think there are at least three. If you take the handbrake out you'll be able to see the throttle rod and two of the bushings. Cant remember whether the third busing is near the pedal end or the trans end. However, all three are just accessible through the various tunnel openings one way or another....

2.4TE · Post by **2.4TE** » Mon Oct 23, 2006 12:50 pm

Gavin,

You were right, the nylon bushes that the throttle rod runs in in the centre tunnel had completely collapsed. I suspect this is the problem with mine and others' cars. Since I replaced the (nylon) gearlinkage bushings last winter, I suspect the lifespan of these nylon bushes is only about 34 years, so many of our cars may be suffering the same problem!

Many thanks!

tanick · Post by **tanick** » Tue Oct 24, 2006 9:33 pm

OK, I finally made the time to deal with this. Took out the floorboards, tunnel carpet, the cover at the back etc. I jacked the car up and disconnected the linkage at the bellcrank. I tried the system between the throttle stacks and the bellcrank. I could get the system of rods in the engine bay to spring back into place perfectly so that the over-run microswitch was operating. I then moved to the front of the car. The gas pedal is nearly new and when I removed it it felt springy enough. The whole of the pedal system looked fine - newly restored although i took the opportunity to hoover out the remains of Maison Blanche that were still in there. By this stage I'd decided the problem's in the tunnel. I lubed the rods going through the bulkhead and the bush at the rear of the tunnel (just forward of the hatch). Finally struck gold and adjusted the hand throttle. This seemed to be snagging a bit so I moved the lump of aluminium forward a bit. I also turned the socket at the front of the tunnel a few turns to shorten the linkage.

Anyway, whatever I did works well I took it out for a drive tonight and did about 30 miles - not one case of the throttle sticking.. I just need to make sure I'm getting full throttle when the pedal's to the floor and I'm done.

Thanks for all the suggestions.