tadpole1969

got a issue that started back a couple months ago, been trying to figure it out, here's what ive done so far , replaced maf, iac oxygen sensors ,coils, and new accell injectors, fixed a vacuum leak on egr valve gasket yesterday but still have the issue , when i get in car after it sets for more than a hour and crank it up idles fine other that the rpms tend to hang a bit seems like , but anyway when i go to put the car in reverse and pull out of yard the rpms start to bounce way up to like 1500 then down to like 500 ,if i dont get on the gas pretty quick it stalls ,yesterday it did this and stalled and was kinda yard to restart , starting to think it may be fuel pump failing ? also fuel filter is new

WJL

First thing first what are you working on? 94 to 98 or 99 to 04.

Have you checked for codes? Fuel pump will not increase the idle

The only thing you haven't replace is the TPS. Throttle position sensor. Not sure what your experience is but if you have a digital meter you can check it very easily.

If you back probe the connector to the TPS with your volt meter turn the key on (engine not running) you should have anywhere between .05 and 1 volt at idle and 4.5 to 5 volts wide open throttle, if you have that you now need to perform a sweep test move the throttle slowly from idle to wide open position watch the volt meter it should increase with no jumps or jerky movements

May not be your problem but worth a try

tadpole1969

yup gonna try that today and its on my 2001 mustang gt 4.6 and no codes at all

tadpole1969

ok i test tps it checked out good to go ,volts before doing sweep test where 1.12 then went up smoothlly while i tapped on tps while opening tb plate open

dawson1112

This is actually probly pretty simple to solve. Your car needs to have the Base idle reset. It has developed bad habits from previous parts that were not functioning correctly MAF IAC ,,, What ever it may be. The adaptive learning has done what it is supposed to do, it adapted to keep the car idling with failing parts. So now the new parts it things it still has to run adaptive messures to keep the car idle where it wants it. In other words your car has to learn to walk again. Disconnect the battery for a half hr or so. Start it up and turn every thing on,, Lights AC to max. Let it run like that for a while,,, then shut it all off and drive the car about 10 miles,, the more stopping the better. There is an actual procedure for doing this, but you will have to google how to do the correct steps as I cant remember them in order.

WJL

I agree with dawson, its at least worth trying, other than that vacuum leak???

tadpole1969

yeah ive already done a idle relearn, i cleared kam with my tuner ,i always clear and relearn for every new part added issue ramains

tadpole1969

correct me if i wrong ,but shouldnt my tps volts be at aleast 1.00 or tad lower on the 4.6 2v?

dawson1112

Should be about .9 volts but I believe they can be as low as .7

tadpole1969

ok yup theres 1 problem ,when i checked my tps sensors voltage from closed position it was at 1.12 , so guess need to lower the idle stop screw until the voltage is in spec with what you said correct?