my toyota 4af carb unstable idl around 700-1400 rpm - Toyota Nation Forum : Toyota Car and Truck Forums

lgene10 · 10-17-2010, 09:55 AM

what do you think is the problem with my car? the engine revs good but the idl goes around 700 and goes 1000 when the engine is hot but when im driving for a while the idl rise again to 1400 a few min. back to 1000 and sometimes 700... its so annoying.. should i change the carb or clean the carb or replace the vacuum hose?... by the way.. the car has just been overhaul after sitting for 1 year..

90 GP · 10-17-2010, 10:39 AM

Check the throttle positioner (dual diaphram unit) on passenger side of carb. It is designed to operate at two speed settings depending on load and deceleration. Sounds like you have a vac line leak on one or both vac lines going to it that is giving the variable speeds. That engine has alot of vac lines so check em all for leaks.

lgene10 · 10-17-2010, 10:56 AM

tnx for the advice.. ill go check the vacuum line tomorrow and take a pic of carb to see if i put the hoses to the right place..

lgene10 · 10-17-2010, 09:36 PM

here is some of pic of carb... there is a one hose missing.. so i connect it from the manifold to the carb..

http://s1231.photobucket.com/albums/...to-0124.jpg%26

http://s1231.photobucket.com/albums/...Photo-0131.jpg

http://s1231.photobucket.com/albums/...to-0130.jpg%26

the engine start fine revs good but the idl is bad and the fuel consumption is not normal 1 liter / 4-5 km my engine eat a lot of gas..

90 GP · 10-18-2010, 05:28 AM

The part that is missing the vac hose connection in picture 8 is called the AAP valve (auxillary accelerator pump). If it was hooked directly to manifold vac all the time that would account for rough running and high fuel consumption. I can't tell where you hooked it up but my guess is that it should be hooked up to the black plastic vacuum switch threaded into engine in picture 2. There is a connection in that pic with no hose attached. If you have vac diagram under the hood check to be sure that's the right spot. Also the replaceable diaphram inside the AAP valve is known to go bad and cause rough running. Get your hose connection hooked to the right port and if symptoms persist replace the diaphram.

lgene10 · 10-18-2010, 08:26 AM

what is auxillary accelerator pump for?... im using the car without hose connecting on it?.. should i replace the diaphram inside the AAP valve?.. btw if the AAP valve is broken or not connected the engine eat a lot of gas?...

90 GP · 10-18-2010, 08:36 AM

The purpose of AAP acts by forcing more fuel into accelerator nozzle to obtain better cold weather performance. It is only supposed to operate when engine is cold below (122 F). When warm over (154 F) the coolant switch shuts it off. That's why I believe it should be connected to black coolant switch I referred to earlier If the diaphram has a hole in it it can bleed in extra gas whether hooked to a vac line or not.

lgene10 · 10-18-2010, 09:01 AM

theres some gas leak from the aap valve pipe.. do you think this is the cost of alot of fuel consumption?.. sorry i do not have any idea what is aap..

btw we clean the carb and rebuild it using carb rebuild kit.. i check the box but i don't see AAP diaphram on it... do you think i can buy it separately?..

90 GP · 10-18-2010, 09:06 AM

I read after I posted that if gas leaks out the vac line connector it confirms diapram is bad and needs replaced. Some rebuild kits have the diaphram but apparently not yours if you didn't have any extra parts. I am guessing a toy dealer should have or be able to order one.

lgene10 · 10-18-2010, 09:17 AM

tnx for the advice ill replace the diaphram tomorrow and search for it... im hoping that i can fix it tomorrow instead of replacing the whole carb.. i want a good idl and less fuel consumption

lgene10 · 10-18-2010, 09:33 AM

hey should i connect the aap here?..

http://s1231.photobucket.com/albums/...oto-0131-1.jpg

tnx

90 GP · 10-18-2010, 03:43 PM

Yes that is where I think the vac line should be connected.

90 GP · 10-19-2010, 08:24 AM

I did a search and found toy part number 21675-35510 for diaphram but there is no picture. The aap diaphram is circular with three screw holes while main acceleraror diaphram is square with four. Need to verify it is the right one. You could try this number at a toy dealer to see if it fits your carb.

https://www.1sttoyotaparts.com/catalogs.html

lgene10 · 10-19-2010, 09:20 PM

yeah its a three screw hole..

lgene10 · 11-08-2010, 09:25 AM

geez i read the box again... and it says carburetor repair kit.. gosh i was too exited rebuilding the engine on that time. btw my father is a diesel mechanic and this is his 1st time overhauling a 16v carb 4af engine im sorry for the trouble .. i think i need to buy a real rebuild kit... i ask the autosupply shop in our town.. and it is not available in our town.. i need to go to a real city to search for it...