I have noticed in the past that my carbureator like to run in high ilde on occasion, basically when it feels like it. Does'nt seem to be a certian situation as to when it only does it. Today, it took the cake though. On my way to work this morning, after about 40 minutes of driving, I had to get on the brakes kinda hard, and my engines RPM's went down like normal, but suddenly shot straight back up and stayed in an insanely high range. I believe it was like 2800 rpms and no matter what, it wouldnt slow back down. I tried hitting the gas hard a few times, thinking maybe the throttle was kinda stuck, but that did not help, and the pedal returned like it should. Finally, when i pulled into my parking lot at work, it slowed back down to a good idel, around 700'ish in drive. In park it was up around 8ish. I think maybe the idle stop solenoid went nuts and got stuck? Maybe? I'm not too familiar with carbs yet, but basically know everything that is on them. Can anybody throw me a bone? The carb on my car is a Computer controlled quadrajet. Thanks fellas!:lala:

 

Oh one more thing, I have cleaned the throttle blades, linkage and basically anything else that moves on the carb with Dragon Fire Carb cleaner and lubricant.

 

Vacuum leak in the brake booster?

 

I second that.

 

Hmm......interesting. I will check out the vacuum line to the booster to ensure it is in good condition and attached properly. Hopefully, its external and not the diaphragm itself if it is the booster. My brakes feel great on the car, no mush pedal, but i will do the simple brake booster test by pumping the pedal to remove all vacuum, then starting the car up to see how the pedal goes to the floor.

 

Ok just went out and checked my brake booster and its vacuum line to the carb was in good shape, and so was the filter, and the rubber hose from it to the booster. I even sprayed water on the vacuum line to see if the engine may bog, it didnt. I sprayed water all over the vacuum lines to the carb and manifold. No bog. I did the brake booster test and pumped the brake pedal till it got all the vacuum out and got hard, then I held it down, started the car and it went to the floor at a slow steady pace. That means the booster is in good shape. Any other ideas?

 

hmmm...I came across one here by accident. This probably hasn't fixed my problem, but i went nuts and decided to start testing Resitiance, and voltage on some connectors and sensors, to veify everything had juice, and was alive. Everything checked out great, except I accidentally left my ECTS (Engine Coolant Temperature Sensor) Unhooked and went down to autozone for some engine degreaser and micelanious items, and noticed the car ran GREAT. On the way home i noticed it even feels like it gained 20 hp. When i got home and popped the hood i seen the ECTS connector off the sensor. Interesting. Needless to say i bought a new sensor since it was only 8.99. Checked the resistance in the old sensor and it read really high at 246.xx ohms, and the new one read only around 5 Ohms I think it was. Anyway the new one reads wayyyyy lower and continued to dwell down. I assume the old sensor was so much higher cause it was hot, and the new was cold?

 

Found out today by another mechanic at work that used to deal with q jets all the time that my throttle plates are worn. The shaft or whatever. Sometimes they are sticking. Guess it's time to just get another q jet.

Today I had a nice experience. On the way to work the idle stuck at 3 grand. Car would start power braking at stop lights. Took all i had to keep it stopped. How do you think I was enjoying that one?

 

I have had this same intermittent prob as you. My posting on the issue included the fact that my G.M. parts guy, as well as two mechanic friends of mine, say that the carb has a design flaw. Furthermore, some people experience it, while most never do.
The replies from the peanut gallery claimed that these guys are nuts, and there is no problem. They felt that it was the accelerator cable.
Imagine my horror, as my car accelerated to 90+ mph, in the Lincoln Tunnel. (under the Hudson, connecting N.J. to N.Y.) The pedal seemed to get pulled to the carpet.
Heavy return springs make no difference. The problem only happens when Jupiter lines up with the Sun. The problem is bound to return. Oooooooooh, can't wait.
The computer does not have enough control over fuel and timing to make the carb do this. Your acceleration issue WILL RETURN.

 

scrap it and buy an edelbrock i did and am very happy

 

I would love an explanation of exactly what this design flaw is, and how it causes your problem.

 

Well, so would I.
My U.P.S. guy has a Camaro of similar vintage, with the 350.
Same problem.
He gave up on looking for an answer, and switched to a different brand of carburator. Oddly, he still uses the computer for timing. Apparently, the m.a.p. sensor gives the computer enough info to run the car w/o the t.p.s..

 

No worries anymore, i have had a AFB style Eldlebrock carb sitting waiting for me to get everything else i needed to do the switch from the computer controlled quadrajet to this good old fashoined tune it yourself carb. Just got the intake manifold today, and already have the non computer distributor. Just need the wiring harness for the torque converter, and my new cam and lifters and im in business.

 

I am happy for you, but this does not exactly address this issue. The Rochester should not have such a dangerous defect.

 

What defect? Tens of millions of them have been made, and you're the only person having this problem. Unless you can say exactly what the "defect" in your carb is, then you don't have a defect.

 

Then I guess that my secondaries really didn't open by themselves. Same for my U.P.S. guy. And the parts manager lied? This problem has only occured 4or 5 times in 5 years. Any normal problem would occur with better regularity. My accelerator cable is fine, and besides, the pedal really got pulled to the carpet. Not my imagination.
It seems plausable that engine vacuum pulled the throttle plates opened, which would raise the mixture needles out of their seats. No other explanation fits the scenario. I have never seen any other carb do this. Aperion-neither of us know everything about everything.

 

The throttle blades are offset on the shafts so that engine vacuum pulls the blades closed, not open.

Whatever is happening to your car could be the result of many things. It could be wear and tear, manufacturing error, or demonic possession for all I know, but it is not a design defect.

A design defect would have to be a recognized problem that showed up in pretty much all units. You'd hear about it every day. Everyone on the board would be sick and tired of hearing newbies ask about it instead of searching for the answer themselves. Lawyers would be filing their teeth.

 

Remember the film "Christine" ?

 

OK guys, I found out for 100% CERTAINTY what the problem was. Actually, it was quite simple. So, you think because your choke is fully open when the engine is warm, or partially closed when the engine is cold is all find and dandy right? Well, in most cases, yes, but there is an exception. WHEN YOUR CHOKE THERMOSTAT STICKS AT A CERTAIN POINT LOCKING THE LINKAGE OPEN SLIGHTLY. Stupid choke thermostat was the problem. Thats it.

 

If you are correct, then I owe you. Thanks for the insight.

 

Oh yeah, I hope your's is this simple too NoTransistors. I know for a fact this was my problem, because I just took the choke off and voila, idle back down to correct range. Been running without a choke for 3 days now, cause I am just waiting to start rebuilding this carb this weekend. Been running like a champ without the choke. No sticking, no problems.

 

Thanks again. I used to have a Triumph with a manual choke. Actually two chokes, because it had two carbs. Never a problem. Started in any weather, on the 1st try.
On top of that, the carbs can still be rebuilt for cheap. Those were the days.