2004 F150 XLT
Regular Cab 8ft Box
5.4 Heavy Duty Payload Package

So I changed my spark plugs last week at 115,000 miles. Not too bad only 6 plugs broke in the head but with the help of Lisle tool they came out easy. I finished the install started her up and everything ran great and can defenitly tell a difference with the new plugs. Drove about 30 miles filled up with gas and went home. Stalled twice going up the driveway. Thats when I noticed the low RPM while in drive and reverse, around 450 idleing and after decelleration it will drop to about 250-300 almost stalling then jump up to 450 again. When I swaped the plugs I had the battery off and the computer out. Its been 4 days and have not had any CEL. The engine is not misfiring and I checked vac lines for leaks and also cleaned MAF sensor with CRC MAF cleaner. The truck runs great at highway speeds with no shaking or shuttering. The problem is only idleing or when slowing and stoping at a red light or stop sign.

Any thoughts on how to fix this would be appreciated.

Thanks

 

I'd start by pulling the throttle body and cleaning it. Make sure the throttle position sensor isn't unplugged.

 

What ill effects would there be if you unplugged the TPS ?? How would you effectively clean the TB without unplugging it ? I am assuming you are referring to the electrical plug.
Thanks for any info glc.

 

Doesn't sound like a coincidence. And the good performance everywhere else tells me fuel and air are fine.

Were the spark plugs gapped to the exact specs? When RPMs are higher, the spark will be robust. At lower RPMs, they might struggle with the fuel coming in to burn.

 

Of course you have to unplug it when you pull the TB to clean it - I meant make sure it's not unplugged now.

Actually, an unplugged TPS should trip a CEL.

 

Sorry glc..had to re-read between the lines, it was late and having senior moments. LOL

 

What plugs did you put in?

 

Goodevening everybody
When I bought my F150 in July last year, the bloke who sold it said"leave that plug unplugged" He didn't knew what he was doing, but in "open loop"the truck was riding smooth but had a harsh shift. when I plugged the TPS ( as I learned later) the tranny shifted nice but the engine had a stutter. After some investgation with a strobelight the ignitiontiming slammed back and forth, due to a wrong LPGkit.
so, the TPS is a very important part,


best regards Ton van der Sluijs

 

Pontiacman, did you ever resolve the problem? I am having the EXACT same issues.

Thanks