: 1970 CDV suddenly started revving high. What's up?



IanW
11-30-12, 04:39 PM
Today when I started up my 1970 CDV the engine was revving high as if the gas pedal was stuck. The pedal was in fact not depressed at all.

Now I have to keep my foot very hard on the brake when stopped in Drive.

In Neutral and Park the high rate of revs is very apparent.

When driving, you can take your foot off the gas pedal and the car keeps going at about 30mph.

Is this likely to be some linkage or cable that's stuck? Or maybe an engine/transmission problem?

I'd be very grateful for some tips on what to look for.

Thank you.

carnut
11-30-12, 06:22 PM
Look for a mechanic and have it towed!

CADforce69
12-01-12, 03:53 PM
Check the accelerator cable. Possibly itīs stuck at some point. If cable is ok, it must be the carb. Maybe itīs the choke which is jammed. If choke is ok, you may check idle adjustment. As carnut says itīs not advisable driving the car until the problem is fixed as transmission could be damaged.

klinebau
12-03-12, 10:17 AM
I also had this problem with my '70 and I am not 100% sure of the cause yet. I have been doing a lot of work to get mine into shape. I have two theories as to the cause. My problem started after I replaced the hoses and thermostat which required a coolant change. I believe that there may have been an air bubble in the cooling system which caused the thermal switch to activate giving me more advance timing from the intake manifold. The next time it happens I am going to look at the timing to confirm.

The only other possible cause I could think of is a vacuum leak in the intake manifold that seals itself after the engine warms up. I already have an oil leak there, so I know for sure that there is some sort of sealing problem.

carnut
12-03-12, 11:59 AM
A vacuum leak will NOT cause a higher idle on a carb'd car.

P.Katson
12-07-12, 01:58 PM
A vacuum leak will NOT cause a higher idle on a carb'd car.

Why? More air is entering the intake which is similar to opening the throttle.

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Sounds like the choke may be stuck on the fast idle cam. With the engine off, open the throttle and try to move the choke flap. Clean the carb linkage with carb cleaner and then lightly lubricate it with WD-40 or similar.

bigm57ict
12-07-12, 02:03 PM
How does a vacuum leak allow more air to enter? Isn't that controlled only by the throttle plate?

carnut
12-07-12, 03:14 PM
I wont dignify the P.Katson post with a discussion. And never use lubricant on carb linkage. Lubricants attact dirt and cause sticky linkage issues.

P.Katson
12-07-12, 03:43 PM
No need to be rude CarNut, we are all here to learn.

You are correct. As a rule, carb linkage should not be lubed, however, many are worn, corroded and can benefit from LIGHT oiling if new linkage or parts cannnot be found or afforded. The problem is most people over lubricate and it becomes a greasy and sticky mess.

Back to the vacuum topic: If you take off a vacuum hose and the vacuum source is below the throttle plates the engine speed will rise. Maybe not as much as a fuel injected engine and it varies depending on the engine and the size of the vacuum hose, but it will increase. Send me a PM if you do not want to discuss here, we both may learn something.