i just replaced the air injection rail and the valve cover gasket of my truck. immediately after this, i began to get this weird vibration in my gas pedal at low rpms. i think the whole motor is vibrating, but its really noticeable at the gas pedal while driving. it happens when i first take off from a stop, and can induce it by making the truck lug a little in high gears. something must of happened when i had it all apart, especially something that has to do with the throttle body. heres some ideas i thought of:

IAC
TPS
fuel pressure regulator; ive heard they can cause vibrations
vacuum leak

i just need some more suggestions about what could cause this and some more info on what the symptoms would be if what i mentioned is the problem.besides the vibration, the truck runs really good.

 

Check to see that something on the motor isn't touching the throttle cable.

 

I got my A.I.R plugged so it does not work any more. I kept on leaking every time it was fixed and it made a bad exhaust leak noise. I had someone do it for me. After I got it back I have all the same symptoms you have. That was 2 years ago and I still have the same problems. I have new motorcrft IAC and TPS. It helped with the vibration some but not enough to be satisfied. Im having fuel problems right now and I am going to hopefully replace my fuel pressure regulator this weekend. I will let you know if it helps any.

 

that was actually the first thing i thought of. i checked it out and there wasnt anything touching the throttle cable

i think the iac and the tps are gonna be the first things i do. definitely let me know how the fuel pressure regulator works out.

 

I just replaced the fuel regulator. I think it helped the vibration some. I just made a trip around the block and it seemed to have helped. The peddle feels heavier and when I give it gas it actually goes. I will be going somewhere this evening and I will let you know how it turns out on a longer trip.
I went with a motorcraft. It was $94 after tax. I would get the part number and look it up on amazon to see if you can find a motorcraft one cheaper.

 

okay thanks alot for the results so far. how hard was it to install? i dont even know where the fpr is.

 

I didn't take my truck anywhere last night but I will be making a 2hr round trip today.
It has three alan head screws and you pop off the vacuum line that is on top and thats it. It is located underneath the intake manifold (1&2). The hard part is getting to the screws. I believe you will need a 5/32 alan wrench. The smaller the alan wrench the easier it will be. After you get it off it just pops off. When I first drove my truck with the new fpr it felt kind of boged down but it got better as I drove it. If you need a pic of where it is let me know and I will try to get one on here of you.

 

okay i will look tomorrow and im sure ill find it. you didnt have to remove the intake plenum to get to it? i just removed the intake plenum when i did the air injection rail and it was a total PITA.

 

i decided to go look at the truck a few minutes ago. i found the fpr and saw that the vacuum line coming from it was broken. i fixed the hose and test drove the truck, but found no difference. however, i do see that the fpr is easily replaced so i will be replacing it this week. heres a picture of the broken line



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double post

 

i replace my fpr earlier today and the exact same thing happened. i had a stiffer pedal and the truck was much more responsive. it even bogged for a minute like you said in your other post. however, my vibration is still there. it didnt change at all, as a matter of fact. mine was 84 dollars at my local parts house. i hate to throw parts at a truck, but i think im gonna do my throttle position sensor next. the fpr did make it run better, so it wasnt a waste. im also hoping that my mpgs will improve (i havent been getting more than 10)

 

Yea same here I'm not to big on throwing parts at it but it can be cheaper than taking it to someone to repair. I would go with motorcraft on the tps. I had a off brand and it didn't help a thing. 10 mpg? I get 14 and I have a brush guard headach rack and the tool box on my truck isn't just for looks.