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Topic: 85 5.0 High/low idle issues (Read 57 times) previous topic - next topic

85 5.0 High/low idle issues

So i have a 85 5.0 and have been dealing with this issue where the car starts and warms perfectly except the fact i have the depress the gas pedal to get it to come off high idle, Except when its pretty warm outside, the car starts without kicking itself up on high idle at all and has trouble on first start without really giving it some gas but once it warms it idles just fine. I was thinking it has to do with the carb choke thermostat but im not sure and dont want to replace a bunch of stuff randomly even though i most likely will anyway. Now this is not a big issue just something more or less i would like to iron out. ALSO when car is idling i can rev the engine and not every time but usually while the car is waiting to warm up it will stick around 13-1500 rpm then i have to press gas again to get it to kick back down. could this be related? i have checked for voltage at the choke thermostat as well and i do have power.

Re: 85 5.0 High/low idle issues

Reply #1
Most of what you describe is normal.
The tension of the throttle linkage return spring keeps the fast idle cam from moving.
You need to push the gas pedal before you start to allow it move to the fast idle.
And you need to push the gas pedal to allow it move off the fast idle after it's running.

There are three steps on the fast idle cam high, medium and low. A vacuum pull down should move cam from high to medium when the engine starts. The thermostat moves the cam from medium to low and then to off the cam.

For the warm weather problem, you can try adjusting the thermostat. You are straining my recall here but I seem to remember scale hash marks or dots and Minus & Plus symbols to tell you which way to move it for more or less choke/idle.

Re: 85 5.0 High/low idle issues

Reply #2
Most of what you describe is normal.
The tension of the throttle linkage return spring keeps the fast idle cam from moving.
You need to push the gas pedal before you start to allow it move to the fast idle.
And you need to push the gas pedal to allow it move off the fast idle after it's running.

There are three steps on the fast idle cam high, medium and low. A vacuum pull down should move cam from high to medium when the engine starts. The thermostat moves the cam from medium to low and then to off the cam.

For the warm weather problem, you can try adjusting the thermostat. You are straining my recall here but I seem to remember scale hash marks or dots and Minus & Plus symbols to tell you which way to move it for more or less choke/idle.

Ah okay makes sense, i knew about pressing gas before start but i did not know it was needed to press gas again to get off high idle i thought it kicked down automatically for some reason but it makes way more sense that way. And i believe you are right on the adjustment i was not sure this style had it so i might have over looked that. Thanks! ill give that a look tomorrow.

 

Re: 85 5.0 High/low idle issues

Reply #3
Been awhile since Ive had a carb.  I do remember having to slightly rev the engine to get it off high idle. 
Mike