Hi

I've been having some interesting problems, let me explain!

Firstly, I've been getting lean codes out of my truck (96 F-150, OBD-2, 4.9L I-6, M5OD) for a couple weeks now. I've installed 2 new before cat o2 sensors, and haven't been able to install the after-cat o2 sensor yet. I have a brand new fuel filter, but haven't been able to install that yet either.

The first wierd problem started a few weeks ago (mysteriously after using Lucas Fuel Treatment i think). Just after start-up, the truck would wouldn't idle and would jerk violently, shaking the whole engine and tranny to crazyness. If i press the gas pedal a lot it comes out of that condition and will rev up like normal, then idle normal when pressure is released from gas pedal.
This happened once in a very long while. It happens a little bit more recently, but I'm used to and good at giving it throttle to avoid it.

This next thing started about 2 weeks ago, and happened to me 3 or 4 times in the past 4 days. After cruising at a relatively high rate of speed (45mph on bigger city streets and 75mph on the highway) and coming to a red light or traffic jam, I lift off the throttle, press the clutch in, and press slightly hard (harder than normal, i try to brake pretty softly though normally), the truck will die...Sorta how the truck will die if you forget to press the clutch and take it out of gear coming to a stop (haven't done that in years). The last few times have been scary, since the power steering goes out suddenly and I'm not prepared to get up on the wheel and stop safely in my lane. The last one (1 of 2 yesterday) happened whilst coming into one of those crub island style right turn lanes, it died after getting off the gas, applying brake and eventually pressing the clutch getting ready to shift down. I almost wrecked my truck bigtime slamming into the curb island and taking down the turn signal poles! The truck wouldn't immediately re-start, I tried twice and it would just crank and crank. I turned off the truck, killed the stereo, air and lights, then turned it back on and applied gas whilst cranking and it started up and idled like normal. Didn't have any trouble after that.


Anyone familiar with this stuff? Is this indicative of some sort of specific problem?

Sorry about making this thread so long, and possibly wasting your time. I will attempt to get this fuel filter I already have installed. From what I know about cars (which isn't much), I'd think the fuel filter could possibly cause these problems (lean, bucking after start, and dieing coming to a stop). I don't think it could be a fuel pump problem, because I think this has happened on both tanks (separate fuel pump per tank).

Other info: 71,000 miles, 5W30 Castrol Syntec, 2.73 rear gear, 4x2, recent tuneup (plugs, wires, cap and rotor), recent coolant flush.

THANKS!

 

Really sounds like a vacuum leak. The leak could be causing the LEAN code too.

Also, since it dies after letting off the throttle, the IAC valve is dirty. Try cleaning it.

 

OK, thanks I suppose I will take it to a shop or the dealership, and see if they can find a vacuum leak.

I'm pretty sure I could clean the IAC valve myself, at least I'll try