lathargic return to idle

[Ryan Wofford]

I have a 1994 ford f-150 with the 300 I-6 and I have 2 problems one I not too concerned about and one I am concerned about however I’m wondering if maybe I can kill two birds with one stone. Problem 1: when I start the truck it likes to spit and sputter for a bit then once revved up (doesn’t do it on it own, the throttle must be slightly depressed in order to start truck) it idles fine, however it only does it when its hot outside when it is cold (less than 50F), it starts fine. *note I am able to replicate almost exactly what the stuck sounds like when I switch from the rear to the front fuel tank however on the front fuel tank I can never get it to rev up and idle so I don’t use it here is a video! https://www.youtube.com/watch?v=4d4ZtJrE78Y. and yes it sounds a lot cooler in real life. problem 2 (not too concerned about): whenever rev my truck to about 4000 rpm (I generally limit myself, the 300 isn’t a HP engine as a lot of you know) it is really lethargic to return to idle compared to the carbureted version of this engine which is almost instantaneous, is there a problem here or is that just how the EFI is on these trucks?
~Thanks for y’alls time

Topic

[college man]

By your description it sounds fuel related that the truck runs better cold which would
mean richer then when warm leans out. but fuel starved. replace the fuel filter would not
hurt to take a fuel pressure reading. By the sound in the video you may have a mechanical
issue with the knocking. more in this link.

http://www.ericthecarguy.com/faq/solving-automotive-no-start-problems

http://www.ericthecarguy.com/faq/solving-automotive-performance-issues

[Ryan Wofford]

I have actually replaced the fuel filter since the video was made with only a small difference in performance, also that knocking is because the motor mounts (which are only 2 years old) are really flimsy for the giant chuck of cast iron that sits on them. Anyways, I have read in some other places about the IAC on these trucks going out, could this be a possibility on this truck?

[EricTheCarGuy]

I would say it’s time to check the fuel pressure and see what you have. Check it on both tanks just for the heck of it. I’d focus on that before worrying about the idle problem. If you solve the fuel delivery issue, it may also solve the idle issue. The links that College man posted for you have several tests for issues of this type. They also include helpful videos, including one on checking fuel psi. Here’s the one I did on solving idle issues.

http://www.ericthecarguy.com/faq/solving-automotive-idle-problems

Please read through those and report back to us with what you find. Good luck.

[Ryan Wofford]

Thanks Eric, I need to go rent/buy some tools, I’ll report my findings to y’all asap

[Ryan Wofford]

Survey says: 40psi while running, however when I shut it off, its about 47, unsure of the specs for this truck but I believe I read somewhere it’s supposed to be around 50-55, but don’t quote me on that

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