does anyone know why this could happen
i have a tbi truck and it idles smooth but the rpms go up and down (w/o ac on). then when your driving you can cruise fine. but as soon as you give it gas to pass some one the motor almost dies . if you floor it it almost dies for 2/3 second then picks up with hardly no power
please help!!!

 

Welcome aboard!

I would guess at one or more of the following: a possible lean fuel issue from something like a failing fuel pump, detonation problems, and a possible weak ignition system or some other ignition problem for starters. Can you scan it or have it scanned while the vehicle is driven in the problematic areas? I would do that and some diagnostics before buying any parts.

 

I changed everything in the ignition system about 3 months ago along with the fuel filter. Do u think it might be the gas? Maybe its bad? But would it mess up from one sec to the next? It was driving fine the whole day and around 6pm it started acting up.

 

If it just up and started running bad and you recently worked on the ignition then thats where Id start looking for the problem. I doubt its the gas unless it started right after you filled up.

 

I say look at your fuel filter installation direction. Then look at the fuel pump (fuel pressure WHILE driving).
Your issue sounds too much like a fuel delivery problem for me to believe it's ignition related. Spark is spark, burned wires won't make your car drive fine no matter WHAT the engine load, you said it idles fine but almost dies when it's floored.

 

Certainly could be a fuel issue, no doubt there, but I had an issue of weak spark causing poor performance under any sort of load. Drove it for a month wondering why it didnt have any power at WOT. Didnt even know I fixed it untill I hit the gas. It was like night and day, Anyway, Ive experienced just about every ignition problem possible and its unlikely that youll run into this so check the pressure under load first.

 

I read this post because my car has shown the same symptons recently.
The consensus seems to be a fuel issue.
I've just dumped a full bottle of injector cleaner/gas anti freeze stuff into a full tank of fuel and since then its lacking when over 2000 rpm. Its hesitating badly under heavy throttle and if raise the rpm over 2K I can hear it struggling, well I feel it more than hear it but you know what I mean.
Mine also crusies fine as well.
Your idle will change when you put the AC on even if you put your headlights on theres a slight change.
It could be just bad gas. The additive I just poured in has made my gas "bad" and it runs like yours.
I'm going to be checking everything in the next day or two anyway. So I'll post if I find something causing a weak spark.
Good luck