Car went from low idle to fast idle out of the blue
Came home during a snowstorm and all of a sudden the idle was too fast. we have rechecked that all the timing is in the right position. we tested the controls best we could with a vacum tester. car idles fine with vacum lines being plugged for timing, but as soon as you reconnect the vacum system it revs way to high approximately 1600rpm at idle. carb screw is backed all the way off, unsure of what is causing the problem. ken
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Start with checking the alternator voltage with a multimeter. With the car off check the voltage in the battery which should be holding 12v charged less if flat of course then start the car and test the battery again. If the alternator is good you should be getting a reading of 14 to 14.5 v if it's the alternator it'll A) not put any charge into the battery or B) be a very low voltage being anything under 13.5 v
You overfilled the tank and screwed up the fuel vent canister. Usually the car will not run, dies while idling, or surges if you try to drive, also if you try to fill up again you might find it difficult to fill your tank fast because the canister is not venting the tank
check the fluid levels in the transmission fluid level dip stick in idle also wipe the stick and recheck it the dipstick is located on the left rear firewall usually a red locking tab .i am re-posting this as im not sure my last post went through
I had a similar problem on my "93 Ford probe. The engine idled pretty rough with shakes, Turned out to be a head gasket leaking engine coolant into the cylinder during low rpm's. At fast rpm's it was fine becuase the internal cylinder pressure was greater than the hot coolant pressure & would prevent the coolant from leaking in.
A friend has the same problem with his "94 Blazer 4.3 L, throttle body injection, manual tranny. He hasn't fixed it yet, It started a few weeks ago & is getting worse. His gets a fast idle with hiccups which causes the engine shake. He already checked the EGR valve. He also has a severe exhaust problem, Not oilly but very gray & terrible smelly, but only when the fast idle problem happens. THis fast idle hiccup problem starts when the engine is warmed up.