I have a 2002 lightning. It is 100% bone stock. It has 22,000 miles on it. The weather here is about 40 degrees. I put only 93 octane in it from different gas stations.

If I try to maintain a constant speed below 30 mph (traffic is bad here), I get a fairly noticeable stumble/bucking. The needle on my tach shows the stumble/buck too. This stumble also occurs if I am very very gently applying the throttle (again in traffic). The truck sputters. Then I give it gas under normal acceleration, I do not have this problem. When I cruise at 55+ mph, I dont have this problem.

I first thought that it might be the truck trying to decide if it wanted to be in 3rd or 4th gear, so I clicked overdrive off and still got the same problem.

Can anyone shed some light on what MIGHT be wrong?

The truck is still under a bumper to bumper warranty, however, it is a GM warranty.

 

I had he same thing with my SVTF when it was stock. I put a K&N and a larger throtle body and it was fine. Try a new air filter first, your filter may be just dirty enough to prevent the motor from sucking in air at low throtle. Hope that is it, cheap and easy fix if it is. If not, sorry, I tried.

 

Thanks for the tip. I have a JLP ram air kit that I hope to install tomorrow. Maybe that will fix it right up.

-Shane

 

Have you tried cleaning your IAC valve? If you are standing on the passanger side of your truck with the hood open it is the small tomato can looking thing on the top passenger side of your plenum. It is held in place by 2 bolts and has an electrical plug going to it.

God Bless,

Suavy

 

How do you clean the IAC valve? Some alky and a tooof brush?

 

Gunk carburator cleaner works very well (white & red spray can available at most auto parts).

 

I had this problem with my '03. When running at a constant speed - anything under 40mph I would get the stumble. My L was heavily modded with KB and all the fixings.

My situation turned out to be a faulty oxygen sensor, BUT - I never got a code so I didn't find the problem for some time. Finally got frustrated and went to my local dealer - $18 part replaced under warranty and I was done.

If the fixes above don't work keep my situation in mind.

Good Luck!

D-Day

 

I just hate dealing with warranty issues. I would HOPE that they could replicate the problem that I have once in a while. If they dont, i am sure i get charged for them looking at it.

 

Dealer should not charge for connecting a Star Tester. I might suspect a coil...especially the firewall coll on the pass side. Remember for warranty you can go to any Ford Dealer. Maybe ask around and find the best Dealer for Service in your area.

Jim

 

Are you throwing an SES light. I had the same problem twice. Sometimes the SES light come on then go off then stay off for awhile then come back on. I also had the problem for a while before the SES came on. It ended up being the DPFE sensor being bad. Your symtoms were identical as mine.

 

No lights. I have a buddy with a scanner. We are going to see what codes, if any, pop up. Then I am going to the dealership.

 

Let us know what happens.

Good Luck

D-Day

 

Update:

Since I have changed to a JLP ram air kit and have done the 'boost bypass mod....

it seems as if my low RPM stumble is gone.

 

my truck has done similar hicups when my fuel filter is dirty,,at tip in or part throttle the fuel pumps are running at a lower psi,,,

 

awesome, hope you found the fix!

D-Day