engine had a mind of it's own today!

[gedmeyer]

I took the '81 out today for a short cruise. After about 5-10 minutes of driving, I gave her a little kick and threw it into 4th. Next thing I know, the car is still accelerating, yet I don't have my foot on the pedal anymore. It was not stuck down and when I threw it in Neutral, it nearly redlined. YIKES! I managed to turn off the engine and coast to a stop along side the road, but I couldn't figure out what made the car do that. I restarted the car again, and it still wanted to max out. I popped the hood and jiggled around with the carburetor for a few. The throttle linkage was not stuck and as far as I could tell, nothing seemed to be jamed or hung up. After about 5-10 more minutes aside the road, I started it up and it was back to normal. I then casually drover her home and she's been in the garage since.
Any ideas on what may have caused the melee? I really fear driving her again until I have it diagnosed and fixed. A similar situation on a windy road or highway may have been catastrophic (for me or for the car!) I don't know a whole lot about carburetors, but it seems to me like it might be an internal problem with the carb or maybe the choke (i don't know why it would kick in at 55mph though?)

Not that I think it would matter, but the car has a new distributor cap, rotor, ignition coil, spark plugs and battery.

 

[clar2001]

All I can do is share a simular story about 6 mounths ago I bought a 75 had a new carb put on so it would pass smoge,so one sunday im on a road the light turnes green, and I nailed it pretty good to see what she do, when I hit about sixty I let off the gas and the car was still going full boar turned key off coasted to the side of the road opened hood thinking broken throtle spring or sothing coulden,t find any thing wrong,so I started the car bam instant red line scary, turn off, pop the hood agin, remove air cleaner this time inside the secondaries is a small brass rod on each side that directes fuel flow one of these fell off and stuck in the throtle body for the secondaries holding it open, from the outside you could never tell, but when I looked down the inside of the carb there it was luckely I was able to retrieve the part it dident fall or wasen't sucked into the engine.
good luck...................

 

[gedmeyer]

Your situation sounds very similar to mine. If that happened to mine, I don't know how I would have gotten it running normal again.

 

[Mako]

Next thing I know, the car is still accelerating, yet I don't have my foot on the pedal anymore. It was not stuck down and when I threw it in Neutral, it nearly redlined. YIKES! I managed to turn

Sounds like a mondo vacuum leak to me. First look for a loose/missing vacuum line hose, touch the carb mounting nuts to make sure it's not loose, verify the throttle return springs are ok and then...

If you have power brakes, disconnect them and plug the hole in the intake manifold. Dittos for any other non engine control (disty etc) vacuum sources like the head lights - remove and plug them.

The idea is to isolate the off engine accessory vacuum lines.

Test the car and see if the problem is gone. If it's not gone, then the vacuum leak is around the intake manifold perhaps.

Add the vacuum lines one at a time and see which system is leaking. A bad check valve allowing the engine to suck air from the accessory vacuum lines is the most likely suspect I would think.

Good luck!
Allen

 

[gedmeyer]

I called up a Chevy mechanic that my father knows and he told me to double check all the linkages and if all seems normal, pull apart the carb and see if there is any crud build up that is making something stick.

If the vacuum lines were the culprit, what whould they make the carb do to go WOT? Isn't there a vacuum pressure gauge that might help instead of having to keep lookign for failure by driving it?

 

[Stallion]

I would think it would be the carb. Because if it's not lubed up enough and your acelerator, of course, first brought up the choke (I think that's how it works, to stop air, and more fuel into it), maybe the choke got stuck.

 

[JohnZ]

Do you have Cruise Control?

 

[gedmeyer]

Well, I pulled apart the carb yesterday and cleaned it all up. Nothing seemed out of the ordinary-no stick or 'hanging up' anywhere. I put it back together and drove it around and never had the problem. Maybe it was a fluke? or a vacuum line that was loose and got fixed when I took it apart and put it back together... I'm not really sure. It's a little unnerving that I don't know what caused it exactly, but I suppose it doesn't matter if I don't run into that problem again?

no...I don't have cruise control.

 

[Pepe Le Pew]

Happened to me one time. I know, its scary when you are on the back roads. Mine was easy. I poped the hood and found the linkage had jammed. If you want to troubleshoot it, I would take it out on a straight highway and punch it. At least you will be prepared to shut it down and pull off onto the shoulder of the road. If it does it again I would pull that air cleaner and take a look at that carb, right after it happens, right along the roadway. Look down the throat and see what is going on. Compare the positions of the linkage from before you started. Move it and make sure those secondaries are closing and that linkage is not sticking. Maybe the problem will show itself. Hope you find it. Good Luck! :s


Kenny

 

[rpounds]

Scary huh? In high school, I had a 58 Chevy with a 348 and a 'slip n slide powerglide'. That old thing didn't have a cable set up for the throttle linkage. The linkage was a solid rod that went to a bellcrank on the firewall. Well, at some point, unbeknownst to me, I broke a left hand motor mount. One day, I punched it and that old engine raised up and caused the solid linkage to hang up . . . scary indeed . . .