Weird 454 TBI problems.... as always

[munice]

Okay well my truck is being a PITA again.

Here's the deal, I've just got the SES light hooked up (swapped in 89 motor into an 87) but not the ALDL so i can't read the codes... These problems have been occuring since the middle of summer But i've been having some difficulties in hooking up the ALDL between the two harnesses.

**no solid codes apparent.. no SES light upon startup..

symptom #1: Driving either in town or on highway engine randomly looses power, (very off and on almost instant between weak and strong) chuggs if I try to accelerate, basically takes more pedal to maintain original speed, very annoying in town as the truck can almost stall if this symtom occurs when turning.. hard to describe, basically a very "pronounced" switch from a healthy big block feel to a "4 million mile small block" kind of feel...
*SES light does not come on.

symptom #2: Engine idles high (no not during starting... thats a noob question) .... actually the engine will idle around 1100 rpm at traffic lights and sometimes stays this way until the truck is shut off again. High idle happens on the highway aswell, I notice this when I'm trying to shift (I don't use the clutch much) The SES light does come on when ever the high idle symptom is apparent. I've noticed the SES light coming on and off on the highway before but didnt notice if it was idling high..

symptom #3: This is the rarest of one, occaisionally the engine will fluctuate rpms between 7-1000 at about the speed of " one mississippi, breath, two mississippi..." SES light does not come on.. does'nt seem to affect driving much if any, just sort of weird.

My theories include:

-TBI throttle body/manifold gasket (these seem to be a well known vaccuum problem child)

-maybe EGR? I've heard that they can cause problems noticeable in highway driving..?

-Bad TPS this im sure is an accomplice if not the sole problem... Just waiting to get a new one... right now ive got a TPS from presumably a 350/305 as it worked fine when i put it on but its visibly different than the original...

old symptom: originally me and my mechanic neighbour decided that my TPS was definitley toast as the truck would run fine until around 2100 rpm, then it would struggle... then above 2100 it would be fine again...

...so I swapped that TPS for one that a friend had he wasn't sure what it was from but it was GM and it fit... and for the initial test run it worked great! the truck ran amazing.. but then it started to have the aforementioned symptoms..


Sorry for the long rambling post but Its just such an annoying problem... It sure takes the cool factor out the big block swap

I might try the old TPS again, but If anyone has any ideas, or If any of you have had similar problems let me know. BTW i hope to swap the front or both of my new axles in this weekend, hope to get pics up!

cheers, Andrew