scary throttle problem - Team Camaro Tech
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post #1 of 9 (permalink) Old Jun 13th, 01, 12:21 PM Thread Starter
Join Date: Jun 2001
Location: Oakland, CA USA
Posts: 4

My car is a 68 RS with the original 327 and 2 speed tranny. Until a week ago it had the original 2 barrel intake manifold and rochester carb. Here is the problem: on occasion, from a full stop as I press the pedal lightly it will sink away from my foot to the floor as though it were being sucked by some vacuum and the engine will rev to wot. I basically peal out and rocket down the street until I stomp on the break, and then it either returns to idle or sometimtes stalls. I replaced the intake and carb with an Edelbrock setup (600cfm) but the problem persists (but now its scarier with the extra horsepower). Otherwise it runs great. Please help before I wreck my car! Thanks in advance
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post #2 of 9 (permalink) Old Jun 13th, 01, 01:43 PM
Join Date: Apr 2001
Posts: 5

I just bought a 69 RS and the same thing is occuring to me. From a dead idle with my foot on the break the car will rev and then take off. Two people have given me different suggestions. One person told me to check the driver side motor mount. Another person told me to check where the vacuum is taken off of the intake - he said I should not have a "T" connection with trans and power brake booster. If you figure this out let me know too.
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post #3 of 9 (permalink) Old Jun 13th, 01, 01:43 PM Thread Starter
Join Date: Jun 2001
Location: Oakland, CA USA
Posts: 4

I've done a little more research and it sounds like the problem could be a bad motor mount. Could anyone explain how a bad motor mount causes the carb to open up all the way?
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post #4 of 9 (permalink) Old Jun 13th, 01, 02:34 PM
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Join Date: Apr 1999
Location: Fortuna, CA
Posts: 26,529

It's the mount! As for the vacuum it's needed for both the trans and the break booster and pulling from the same manifold source won't effect the throttle!!

What happens is when the engine is rev'd it torques and pulls up on the driver side mount. If broken the engine will lift higher than it should on the driver side. This in turn is causing the engine to rev. Normally you step on the gas and the rod is pushed closer to the stationary engine opening the throttle. Think of the rod being stationary and when the motor lifts it opens the throttle...

You want to fix it as soon as you can!!

'69 RS Convertible w/SS trim
'96 Z28SS #1679 of 2410
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post #5 of 9 (permalink) Old Jun 14th, 01, 10:24 AM Thread Starter
Join Date: Jun 2001
Location: Oakland, CA USA
Posts: 4

thanks for the help. i'll change out those motor mounts asap. is this a difficult job? do I need to lift the motor out of the car or just raise it enough to slip on the new mounts? Thanks again.
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post #6 of 9 (permalink) Old Jun 15th, 01, 01:22 AM
Join Date: May 2001
Location: Mooresville IN
Posts: 19

Just raise it up enough to slide the old ones out and the new ones in....It should only be a couple hour job,if you have never done it....They realy aren'tthat bad

Good luck man
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post #7 of 9 (permalink) Old Jun 15th, 01, 11:53 AM
Join Date: Dec 2000
Posts: 14

It is the mount. I had the same problem on my 67. Here is what you can do. With the car in an open driveway have someone or do like I did. I used a camcorder on a tripod to watch the engine. Don't stand in front to watch it!!! Now apply your brake hard, put in drive and gently apply gas. If motor mount is broke your engine will rise on the drives side. Mine went up 4+ inchs, this causes your gas linkage to open up the throttle more!(cool video) BE READY TO TURN THE IGNITION OFF!! It may want to runn away. If this sounds too scary then just use a block of wood on a floor jack under your pan (do not try and jack the whole car up, u will crush the pan)and if the engine raises more than a 1/4 inch replace the mounts.
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post #8 of 9 (permalink) Old Jun 18th, 01, 06:41 AM
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Join Date: Sep 2000
Location: Washington, Michigan USA
Posts: 7,728

This was the biggest recall in GM history - left mount separates, engine rolls to the right, jams throttle wide open. Field fix was a cable wrapped around the left upper "A"-arm shaft to the engine, production fix was the "interlocked" engine mount. Many cars are still out there that never got the recall fix.

'69 Z28 Fathom Green
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post #9 of 9 (permalink) Old Jun 18th, 01, 09:48 AM Thread Starter
Join Date: Jun 2001
Location: Oakland, CA USA
Posts: 4

Thanks for the help everyone. I found both of my engine mounts were completely sheared in half! I replaced both of them and the transmission mount this weekend. Not the most fun I've had working on the car but very worthwile. The throttle problem is fixed and the car generally feels sturdier. It also solved a high speed vibration problem I was having (I guess from the enging dancing around un-tethered.) Many thanks!
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