Chrysler Repair: rough idle, surge, gas tank, fuel injector

Question
I have an Intrepid with the 3.3 liter v6, 150,000 miles. In the last year or so, the idle varies like it's missing sometimes, or varies when I accelerate. Funny thing is, if I put it in low and drive the rpms above around 3500 for a little bit, it's ok for a while. But after a few minutes, it's back to the surging. No check engine light. I changed all the plugs but one last year (couldn't quite reach it). I haven't changed the wires yet. I've tried the fuel injector cleaner in the gas tank. Any ideas?

Answer
Hi Tim,
You didn't mention the year but even though the engine light has not come on, there still could be a fault code stored in the computer memory. You might get a handle on that using the ignition key:"on-off-on-off-on and leave on" doing that in 5 seconds or less elapsed time. Then watch the check engine light, which remains "on", to begin to flash, pause, flash, etc. Count the number of flashes before each pause. Then repeat to be sure you have an accurate set of flash counts. Then group the counts in pairs to form the 2-digit fault codes. Then write back or go to www.allpar.com/fix/codes.html for a code list. We can go from there. If that doesn't work then get a free code readout at an Autozone parts store using the multi-pin OBD-II code system which produces 4-digit codes instead.  
That check for codes is the best way to start to find out what is wrong.
Sorry for the delay. Your question just appeared in the "pool" this morning.
Roland