I think I may know the answer to this one but I drove the Mustang to work today and everything seemed to be running basically ok. I had noticed at one stop sign the car was "slipping" a bit like the master cylinder was going out or someone was hitting the gas.

When I got to work and pulled into a spot the engine was racing after I put it in park. At first I had to look to see if I was pushing the gas by mistake instead of the brake.

One thing I can think of is this morning I looked under the hood checking out a rattle type sound and tightened down my air cleaner bolt...not a lot but a little.

Any chance this could tighten it down just enough on the carb to be causing the throttle to stick?

 

if it happens since you bolted down the aircleaner the aircleaner housing might rub on throttle linkage.
So leave the aircleaner on and slowly turn the throttle by hand to see if anything interferes.
What happens quite often on 64-66 models is that the linkage is worn. it is that linkage where the rod from the throttle goes towards firewall and meets that part that is coming from the pedal. If the rubber in there is missing and the thing is flopping all over the shop then this is most liklely your problem.
be warned: a sticky throttle is a very dangerous driver, especially in an auto where you have no clutch

 

Thanks for the advice and I agree regarding the danger. It was doing fine this morning then only caused a problem when pulling into the garage.

The good news is the house is only about 8 minutes away so I won't be going far if I go anywhere at all prior to figuring it out.

The only other thought I just now had is that my new carpet is thicker...any chance it might be sticking on the pedal end of things?

 

also, check and see if the retainer for the return spring hasn't loosened up. It runs from the linkage to the back end of the manifold. One last item, if you've work on your carb, and had it off the car, make sure the butterflies open freely when bolting the carb back on.

 

Ok, this continues to be confusing to me and any advice or ideas would be great.

Car ran fine coming to work until I pulled into a spot at work and put it in park at which time it seemed to be running fast at idle. I got in it at lunch and it still seemed to idle fast until I put it in reverse then all seemed well. I drive to the bank, pull in a spot and soon as I put it in park it idles fast again. So I start thinking ok maybe the idle is set to fast now because of something we did last week.

Get back in the car and start her up at the bank and it seems to be running fast again till I put it in reverse. So I drive around for about 10 minutes then pull into the sandwich shop and idles fine when I pull in a spot and idles fine prior to putting it inot reverse when leaving as well. I come to the office, pull in a spot and put it in park and normal idle again till I turn the car off.

What the heck was going on with that? It was only the idle that seemed really fast but seems to have resolved itself (for the moment at least). Could it be that it is cool outside today and it got better with heating the car up from driving some?

Or was the throttle stuck some and the issue worked itself out....?

 

I had a similar 'fast idle' quirk that came and went several times. Drove me nuts especially since it was a newly rebuilt pony carbs 4100.

Turned out to be a sticking secondary throttle that the linkage behind the choke that closes the secondaries was never properly set by pony. Allowed the secondaries to stick about 1/16" open.