4A-F varying idle speed - Toyota Nation Forum : Toyota Car and Truck Forums

darth-grantius · 08-17-2009, 02:18 AM

Hey guys.

My 4AF idles differently at random occasions. Im not meaning revving higher when cold - im meaning when the engine is warm with no electronics on it sits at 1000rpm mostly - but sometimes in the same senario it sits at a much better 750rpm. what causes this variation, and could it be a cause of my bad fuel economy?

TonkaTom · 08-17-2009, 03:03 PM

With my lights on I idle at 1k. Sometimes when it is colder outside I will also idle at 1k. Does the engine sound smooth?

darth-grantius · 08-17-2009, 05:06 PM

Quote:

Originally Posted by TonkaTom

With my lights on I idle at 1k. Sometimes when it is colder outside I will also idle at 1k. Does the engine sound smooth?

yes its smooth. any other ideas?

90 GP · 08-17-2009, 05:14 PM

Check the vac lines for leaks on the dual diaphram throttle positioner . It's on passenger side of carb. It has two speed settings to raise idle when any load (electrical or otherwise) is put on engine and a lower setting for idling. Any vac leak in the connections can cause what you describe.

fredricktflail · 08-17-2009, 08:04 PM

Yes, check vaccume.

darth-grantius · 08-17-2009, 09:24 PM

Quote:

Originally Posted by fredricktflail

Yes, check vaccume.

would this cause bad fuel economy?

TonkaTom · 08-17-2009, 09:57 PM

Is your fuel economy a problem?

darth-grantius · 08-17-2009, 09:59 PM

Quote:

Originally Posted by TonkaTom

Is your fuel economy a problem?

yes. my car drinks so much for its size.

darth-grantius · 08-18-2009, 12:22 AM

Quote:

Originally Posted by 90 GP

Check the vac lines for leaks on the dual diaphram throttle positioner . It's on passenger side of carb. It has two speed settings to raise idle when any load (electrical or otherwise) is put on engine and a lower setting for idling. Any vac leak in the connections can cause what you describe.

how do i check if its leaking?

***SCT*** · 08-18-2009, 01:34 AM

One way of checking for vacuum leaks: Take a can of aerosol brake cleaner, carb cleaner or anything aerosol liquid flammable alike and spray in small sections around the vacuum lines. If the engine RPM raises/ fall/ change, the leak is within that vicinity you sprayed.

darth-grantius · 08-18-2009, 02:27 AM

Quote:

Originally Posted by SCT

One way of checking for vacuum leaks: Take a can of aerosol brake cleaner, carb cleaner or anything aerosol liquid flammable alike and spray in small sections around the vacuum lines. If the engine RPM raises/ fall/ change, the leak is within that vicinity you sprayed.

nope not a difference. however - i drove it today. would the angle of how im stopped change the rpm considering its carb?

j2b4osan · 08-18-2009, 09:13 AM

old carbs just act funny sometimes I rebuilt the whole card re-tuned and replaced nearly everything and my idle still changes sometimes. its not a big change so I wouldn't worry about it, it may just be the rad fan anyway. or could just be a failing diaphragm. I also feel that the amount of weight you have in the car drastically changes its gas mileage. so if you carry tools or something in your trunk all the time try taking it out.