Good evening guys,

Well the title says it all, and yes I did a search. Recently my truck has developed this idle quirk. My truck starts fine and sometime idles a 650rpm but sometimes it idles at 800 rpm. But the real problem when I start driving the idle remains high sometimes running at 2000 rpm. When I push in the clutch going down the road the idle will stay at 2000rpm for a second then drops slowly down to approx. 1000 rpm. I changed the IAC in early Jan. on a unrelated issue. I know this can be fairly common problem but a couple pointers where to start would be great.

 

IAC would be the main culprit.
But you changed it.

Check it again just incasers.

And then check your FPS, and your TPS.
If the TPS is not working right, it will send bad signals to the computer, telling it for more fuel.
I greased my stuff on the top of the TB too when i changed mine to try to avoid any stickyness.

The FPS could be bad, it might be sending to much fuel when you slow down. pull the vacume line off, and check to see if it smells like fuel. If it does, its bad. I dont know of any other way to test them, but swaping them out. Anyone else know FPR tricks?

Pull the codes too. Might have a bad O2 sensor, or something reall... crapp, you got a 96. It is probably obdII.....
uh. If its OBD2, goodluck! haha.

 

Also, you might want to scrub your throttle body, and then check for vacuum leaks around the intake area. I had that same problem for over a year. I checked all the tps, iac, cts, etc. But last week I finally had to replace my valve cover gaskets, and in the process put new throttle body and plenum gaskets. I soaked and cleaned everything before I reinstalled it on the truck. Now for the first 10 minutes or so, my idle is around 1200 or 1300, but after 10 minutes of driving, my idle is a solid gorgeous 700rpms.

 

Pull the codes. What you describe is exactly what mine was doing. I replaced the throttle position sensor and everything is fine now. My truck is a 1995 F150, 351W automatic. I'd look at the TPS as a strong possibility.

 

Thanks for all the suggestions guys I haven't have chance to do much. Work and school have been crazy, vertical welding really sucks. I'm going to try and start later this week going through the paces.

 

what is the best way to clean a throttle body, as I have never done that before. anything in particular not to do or use? any help is greatly appreciated

 

my gf sunfire did the some thing . bad computer it ran like gold for awhile and then like dirt . i taped the computer with my hand when it run good and it started to run bad right i taped it bad computer.

 

DONT CLEAN YOUR TB!!!!!!!!!!!

its coated on the inside, there is supposto be a sticker on it that says dont clean!!!

 

Lol! I know I've seen that in many posts. I have not tried to fix it yet because I've been really busy.

 

That is a joke right?

 

No it's not. The TB has a special coating. And when you clean it you remove it after that your TB will get dirty faster.

 

My 89 F150 5 litre did the same thing. Very erratic idle. Changed TPS and IAC. Now it only changes idle slowly ( but still does ). Fuel pump is VERY noisy and buzzing goes up and down with idle. I'm about to replace the pump. If your pump is noisy, have that checked as well as sensors mentioned as that can affect running too.