Hey everyone,

I have an issue with my 99 f-150 4.6. This has happened about 25 times in the past 8 months. I first noiced it when I was slowing down at a traffic light and I was nearly at a complete stop and the truck felt like it wanted to continue on its own and I needed to really put the brakes on to stop the vehicle. I put it in nuetral and the RPM's slowly went up to between 2000 and 2500 then would slowly fall to a normal idle. I blipped the throttle and the RPM's once again stayed at 2000-2500 rpm's then slowly fell. This is not a totally repeatable problem but when it happens it stays around for a while. Sometime aggressively blipping the throttle it will fix itself sometimes not. Any help/idea would be greatly appreciated.

Andrew

PS I cleaned the IAC and throttle body about 14 months ago.

 

ive seen this happen on the ford rangers a couple of times. they needed new iac's. i'd clean the throttle body and replace the iac at the same time. but when its intermitent its hard to really know if it fixes the problem.

 

Matts ford,

Could anything else be the cause of this, like a bad TPS or possible vacuum leak. thanks again.

Andrew

 

both of those could also be the problem. spray a carb cleaner around the intake and some vacuum lines.and see if it gives you any running issues. and check to make sure that your pcv hose isnt sucked shut because sometimes they rip little holes in them and they take in a little bit of air. and also blow off anykind of sand or dust that is around the throttle body in case it is a sticking throttle.

 

Check all the PCV hoses, they are bad to rot and leak under the wipercowl near the rear of the left valve cover. It wouldn't hurt to clean the IAC again, the 4.6 only take 10 mins to clean, so its a quick fix, but if the spring is worn it will need a new IAC.

 

So where have you been? - back from R&R..

 

hey everyone,

It has been a while since I posted any up dates to this problem I have been having. With my crazy work schedule and all the overtime I have had to put in at work. I finally got around to replacing both the IAC and the TPS on my truck and so far knock on wood the problem is gone. I checked over every single vacuum line and none of them where cracked so I just decided to replace these sensors. thanks to everyone for all of the good suggestions you guys steered me in the correct direction to cure this problem.

andrew

 

I don't know what brand of air filter you are using, but you're probably using a NAPA, or a K&N. Switch to Motorcraft, and you won't have any more problems... Except having to change the filter more often.

I'm a farmer, and we have many ford vehicles on the farm. We had TERRIBLE problems with IAC valves and cruddy throttle bodies until we switched to motorcraft filters. I can tell you that motorcraft air filters are FAR superior to any other brand. They are a very tight weave oiled filter. The only negative to them is that they stop up very quickly and they don't blow out very well...