Idle issues

[junkyardjeff]

Disconnected the speed sensor and it will stay running,what in the rear end can cause the sensor to act up..

[rooster]

Disconnected the speed sensor and it will stay running,what in the rear end can cause the sensor to act up..

I went to auto zone site and they have a sensor in the rearend called ABS brake sensor, they also have a additional sensor that fits into the trans called speed sensor.

there are different sensors for auto tran and manual trans.

Something not right!

Is your truck obd1 or obd2?

[junkyardjeff]

I have seen both sensors and my trans is made for one to bolt in but has a plate over the hole but the truck originally never came with the trans mounted sensor and the truck the trans came out of never had one too,its OBD I.

[rooster]

I have seen both sensors and my trans is made for one to bolt in but has a plate over the hole but the truck originally never came with the trans mounted sensor and the truck the trans came out of never had one too,its OBD I.

There's a lot of talk about it over at f150 net, and its the same complant you have. It sounds like it could be either way, might depend on trans model.

[wayne petty]

have you cleaned the throttle blades and the throttle bores??

set the base idle.

warm up the engine to operating temp.. unplug the idle air control valve.. adjust the idle stop screw so the engine will idle at a very low speed in park but not stall...  plug the idle air control valve back in.. shut the engine off.. count to 15 .. restart..  see what happens..


if that does not cure it..  pick up your vacuum gauge..  put a 5 foot hose on it..  put a TEE in the end of the hose.. put a one inch section on one of the branches..  on the air injection system there are 2 valves the TAB valve is right at the back of the smog pump.  thermactor air BYPASS..  its the other one you want to check..  it is the TAD...   thermactor air diverter valve..  cold start you should not have vacuum for 10 to 15 seconds to that valve..  after that you should have vacuum except when hard accelerating or decellerating..   no vacuum results in the air injection being DIVERTED To the exhaust manifolds or exhaust ports depending on which heads you have.. this dilutes the exhaust stream when computer is looking at how much oxygen is left after combustion to know where to set the air fuel ratio at..  it will screw up the way the engine idles and ruin your fuel economy also.. melt your cats.. crystalize your exhaust manifolds.

you will have to verify the crossover tube is NOT rotted out. that the check valves actually function..  yes.. you will have to apply suction to them.. they should allow only air to be blown thru them.  you will have to verify the diverter valve works as designed and does not leak air to one of the ports when vacuum is applied.   with vacuum the air goes to the downstream pipe that enters just before or in the middle of the converter.

while you have your vacuum gauge out.. tee it into the green hose that feeds the EGR valve and take it for a drive.. warning if your speedometer does not work..  you may NOT get EGR operation.. and your motor may PING..  if you get the speedo working. you should have progressive vacuum applied to the EGR valve starting just as you  reach 8 or 10 MPH.. plus or minus.. and max vacuum should be in the 40 to 50 mile an hour range.

there are also vacuum hoses up under your upper plenum.. there is one that comes out the front and passes the front of the passenger side valve cover that is the Canister purge hose..  they tend to leak where the hose rots off up under the manifold where its hard to get at.  i usually have to use a 3/16 x3/8 vacuum nipple and a short piece of 3/8 hose to repair that.. same thing for the back.  where is will feed the MAP sensor on versions with map sensors.

the PCV on the 5.8 is trapped under the upper plenum in the valve cover.. i have only found 4 or 5 of them over the years where the hose in the back was disconnected and plugged..  please try to use a motorcraft PCV valve if you can get one..  its an EV-68C in motorcraft..  the idle control system depends on an calibrated air leak to maintain idle speed.  if the PCV is plugged or wide open. you won't get the proper idle operation. if you use a NON motorcraft.. you get it by shape not calibration.. one shape fits all.. so they make one with the biggest opening  this results in oil being consumed at about 400 miles per quart..  you don't want to know why i know that.

[junkyardjeff]

It was a bad speedometer that was causing the problem,took it from the track that donated the trans and working fine.