I've got a few problems with my truck and hopefully someone can point me in the right direction. It's a 1996 F-150 XL 4.9 2WD and has had ongoing hot start issues and a lean code for bank 1 and 2. Recently the truck developed a persistently high idle once operation temperature has been reached. I could put the transmission in gear and it would take off without any input from the accelerator pedal.

I decided to check the IAC. Took it off and put some power to it. I could hear it clicking but could not see the pintile moving and it was pretty corroded, so I replaced it with a Delphi. While I was in there, I also removed carbon from the throttle body (it was sticking a little). The vehicle now idles great, but I am still getting a slightly sticky throttle. It takes a few seconds of letting off the gas pedal before it starts to slow down.

The butterfly valves appeared to be clean and functional after I finished. I didn't notice any thing abnormal with the throttle cable itself. I'm thinking my next step is to check the throttle position sensor, what do y'all think?

 

Don't attempt to clean the throttle bore - it doesn't need it, and there should be a label on it warning AGAINST cleaning it. It's always OK to test anything, if you follow the published diagnostic procedure. Do you have a Haynes manual?

You should put ALL the truck's details & history (as much as you know) into your signature so it shows with each post, as this page explains (the site may be down at the moment):

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Phone apps don't always show signatures, so you may need to switch to a real browser in desktop mode on your phone, or just use a desktop/laptop computer. Put your location (nearest city) in your profile & upload an avatar of the truck. The more pics you post of the truck, engine, wiring, labels, & undercarriage, the more likely we can help you. Not all its details are relevant to these issues, but you don't necessarily know which ones are relevant, so just put everything in now.

 

Already done. I did my research on cleaning the TB and concluded that the protective coating that allowed copious amounts of carbon to accumulate had already been compromised. If it needs to be cleaned more frequently because I've stripped off what little of the coating remained then I'm prepared to do so. The truck is running substantially better after replacing the IAC and cleaning the TB, enough that it is drivable when it previously was not (idle was high enough to cause an overheat). I will go ahead and check the TPS resistance next.

 

I would check the larger hoses for the PCV valve and the brake booster for a vacuum leak before doing anything else.

 

Don't worry about cleaning your T.B. I have done mine a couple times before and never had a problem. You just don't get agressive doing it.Sometimes they will get some accumulated carbon preventing the throttle blade from working freely or the bore for the IAC pintle. What are you supposed to do, obey the warning label and throw it away?

 

Your conclusion is wrong, based on a wrong assumption. The coating is NOT there to prevent accumulation.What will you check it for? Resistance is NOT a published test for the TPS.

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Where are you coming up with that? How about: obey the label, and leave it alone?

 

I appreciate the comment. I haven't lost a minute of sleep worrying about whether or not I should have obeyed the warning label.

I will check for vacuum leaks. I really need a smoke machine to properly test it and not waste time.

 

Well if you suspect its the throttle cable its easy to see if it is....Just pop the cable off of the throttle arm and then hit the gaspedal...The pusher spring should return the cable to full extension..If not replace the cable...

If cable returns to full extension Id try the throttle arm to see how it feels without the cable...On one of my throttle bodies there was so much wear between the throttlebody and the butterfly disc shaft that it caused the blades to stick..

Also the reason why they say not to spray cleaner inside the TB is because theres a nylon coating on the shaft to create a seal aswell as give it a way to not get sticky...Carb and TB sprays take that coating off the shaft causing the shaft to have side clearance.....The way I fixed mine was to open the tb all the way and slightly opened up the bore with a scotchbrite pad until it stopped sticking...



Sometimes you can remedy the issue by loosening the disc screws and retightening the screws in an attempt to reseat the discs to the new shaft angle...

Good Luck

 

The coating is not on the shaft - it's on the TB bores. And abrasion removes it faster than solvents. It's described here:

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So I have a 1996 f150 that brings up the RPMS without even touching the throttle and ive noticed it's higher then average when compared to a cold start. Then it stops and starts back up again. I saw a previous thread on the cruise control unit and removed it. Still has the same problem. I saw the TB and it didn't move when the RPMS was raised to probably 1,500 to 2,000. Maybe 2,500. The throttle position was still in the idle position. Looking for assistance because I'm outside of my own area on my own truck