Stumped

[BLZNFUN]

Hey all!

I have a 1993 Chevy S10 Votec (W) 256,000 miles on it. It runs awesome for the mileage and such, but I am having a few anomalies with it that give it the hiccups lately. I will attempt to give a little background in to the vehicle...

I bought it about 13 years ago. It had roughly 155,000 miles. 4X4 was out, front end was shot and once in awhile it ran like crap (and exhaust smelled funny like really sulfury.). Over the course of several years of ownership I have replaced the following (Some repairs are not related to my current problems):

EGR - About 10 years ago
MAP - about 5 years ago
TPS - About 2 year ago
IAC - Just a couple of weeks ago
Radiator - About 1 year ago
Transmission - About 4 years ago (I'll get into this shortly)
Spider Injector Return Line - About 5-6 years ago (Leaking)
Knock sensor Driver side - About a year ago (Didn't know there was two, going to replace the other one pending input)
Distributor - Couple of weeks ago
Temp sensor (Gauge) - About 1 year ago

Ok, about 4 years or so ago, my transmission started to shift 1-2 really hard to the point it finally took out the transmission. I took it to a local reputable rebuild shop (Private owner). After determining the vehicle still had lots of life left in it, I decided to rebuild the tranny. It is a 4L60E. But months before the transmission went out, it would flash the check engine light. Being sporadic, I didn't think much of it. Turns out it was a code 43, which after research turned out it could be the knock sensor. However, after the transmission was repaired (and promised all my shifting problems would be solved) it still shifts super hard sometimes that it shutters when it shifts. However, sometimes it shifts so smooth, you barely can feel it. So I thought maybe it's this knock sensor now working that is telling the transmission to shift hard since possibly some of it is based on where timing is on how hard to shift? $400 later and one knock sensor, it still throws the code. This sensor was "welded" into the block so hard from age, it didn't want to come out. The mechanic finally got it to come out. I wanted him to diagnose it to see if it really was the problem, but he just went ahead and replaced it. The problem still persists. Just recently, my distributor started to make noise occasionally (like a squeal) so I knew it was time to replace it. Again, I was anticipating that maybe this would fix the code 43 since maybe the distributor wasn't advancing correctly and blaming it on the knock sensor. Nope. That's when I found out there are two knock sensors. One on driver side, side of the block and one behind the passenger head between the firewall and the engine.

Before I had the distributor replaced though, occasionally it would start surging at idle. After the distributor was replaced it got worse (The mechanic did find some vacuum lines off on the back of the engine so there shouldn't be any vacuum leaks). It would actually stall out, almost feeling like a miss when it does catch and not die. Mechanic recommended I replace the IAC, which I did. The surging/dying still exists. I didn't notice anything while driving until just a couple of days ago. Now, when holding constant speed just past the point of torque converter lockup, I can feel the lockup disengage and re-engage as if I was slightly taking my foot off the accelerator.

Before I go dumping more money into it, I would like some input on the hard shift, specifically what controls it (tranny shop thinks its something isn't controlling the line pressure correctly) and if possible, how to fix it and if any of my ideas were or were not correct with the ignition controlling a part of it. Also, what's causing the surging and code 43. At this point I am almost thinking of replacing the computer.

I was also thinking the surging/dying could be caused by the EGR. Back when I replaced it the first time, I recall it doing the same thing or very similar. Really stinky exhaust, surging/loping, almost to the point of dying.

I know the vehicle is old and probably not worth it, but we got a lot of miles together, and right now I just can't afford to replace it. I plan on driving it till the next major breakdown. (It has a main bearing knock until it builds oil pressure up from idle)

Thanks for listening guys (and gals)!