idle going up and down
Thread Starter
918eva
Joined: Jun 2015
Posts: 1
Likes: 0
From: Northeast oklahoma
idle going up and down
Just bought a 88 f150.my friend did the test drive.i noticed when i start it it idles up and down.i dont know if it continues after warming up or not but its not like its idled up until it gets warm like a vehicle might do.its like ur reving the engine up
1994 F150 XLT 5.8L 2wd
Joined: Mar 2014
Posts: 2,150
Likes: 249
From: Iowa
Pull your codes:
https://www.f150forum.com/f10/how-re...es-obdi-10907/
Then try starting the truck with the IAC (idle air controller) connector unplugged, unplugging it while running doesn't work well to test it. If it idles normally when it's started with it unplugged then it needs replaced. You can clean it to "limp" it along but once they start giving you problems they will continue until replaced.
If problem still there when started w/o IAC the next step is to test the TPS, should read .9-.97v closed throttle, 5v WOT, with a smooth increase as the throttle is opened up. You can adjust it, if you can't get it in spec then replacement is necessary. When replacing, or if the current one is not Motorcraft brand, Motorcraft brand is mandatory for this item (along with PCV).
If in spec and still having problems then you need to test your small diameter vacuum lines for leaks, best way is with a vacuum pump/gauge, other "spray" tests can locate large leaks but smaller ones can only be found with vac pump/gauge. ($30 for mightyvac pump/gauge on amazon was one of the best investments I've made to date, can use it for multiple things and it has paid for itself over and over again in saved shop fees). If the small diameter vac lines need replaced I recommend these (http://www.siliconeintakes.com/silic...686d47fdf65361), 22ft of 4mm hose will do all of your vac lines. Just like plug wires, one at a time and it's super simple, the only thing you will need is a 4-way vacuum tee (or two 3-way tees) for the TAD and TAB systems.
Wouldn't hurt to do a fuel pressure test as well, can "borrow" a FP tester from auto parts stores. Do the test with key on/engine off, engine running, and again 2-5 minutes after shutting engine down.
Report back with what your problem was if you figure it out (to help others) or let us know if this didn't work and we can dig further into less common issues.
https://www.f150forum.com/f10/how-re...es-obdi-10907/
Then try starting the truck with the IAC (idle air controller) connector unplugged, unplugging it while running doesn't work well to test it. If it idles normally when it's started with it unplugged then it needs replaced. You can clean it to "limp" it along but once they start giving you problems they will continue until replaced.
If problem still there when started w/o IAC the next step is to test the TPS, should read .9-.97v closed throttle, 5v WOT, with a smooth increase as the throttle is opened up. You can adjust it, if you can't get it in spec then replacement is necessary. When replacing, or if the current one is not Motorcraft brand, Motorcraft brand is mandatory for this item (along with PCV).
If in spec and still having problems then you need to test your small diameter vacuum lines for leaks, best way is with a vacuum pump/gauge, other "spray" tests can locate large leaks but smaller ones can only be found with vac pump/gauge. ($30 for mightyvac pump/gauge on amazon was one of the best investments I've made to date, can use it for multiple things and it has paid for itself over and over again in saved shop fees). If the small diameter vac lines need replaced I recommend these (http://www.siliconeintakes.com/silic...686d47fdf65361), 22ft of 4mm hose will do all of your vac lines. Just like plug wires, one at a time and it's super simple, the only thing you will need is a 4-way vacuum tee (or two 3-way tees) for the TAD and TAB systems.
Wouldn't hurt to do a fuel pressure test as well, can "borrow" a FP tester from auto parts stores. Do the test with key on/engine off, engine running, and again 2-5 minutes after shutting engine down.
Report back with what your problem was if you figure it out (to help others) or let us know if this didn't work and we can dig further into less common issues.
I
Joined: Feb 2014
Posts: 827
Likes: 37
From: Jonesboro, AR
idle going up and down
fltdriver that is very interesting about using a motorcraft only tps. My truck never seems to have a stable idle. Especially on a cold start it goes up and down until it warms up and then does it again after restarting (whether its warm or cold). I replaced my bwd IAC valve with a motorcraft which helped stable the idle but it still isn't right. I am currently running the cheap masterpro tps do you think that is my problem?
Senior Member
Joined: Jan 2013
Posts: 171
Likes: 18
From: River Falls Wi
fltdriver that is very interesting about using a motorcraft only tps. My truck never seems to have a stable idle. Especially on a cold start it goes up and down until it warms up and then does it again after restarting (whether its warm or cold). I replaced my bwd IAC valve with a motorcraft which helped stable the idle but it still isn't right. I am currently running the cheap masterpro tps do you think that is my problem?