My son's 1993 blazer started stalling when approaching stop lights, and the idle would rise and fall. then within a day, hardly runs at all. We've replaced the TPS, both coolant temp sensors (for gauge and for engine), the distributor assembly, cap, rotor, plugs, wires, IAC. I had it running great in the driveway, engine revving, idling, thought all was good. Then the test drive. Didn't make it a half mile. Bucking, cutting out, finally stalled and won't restart. The fuel pressure goes to 60psi when key turned on, drops to 55 almost immediately, then when the relay clicks, it drops to 52psi. Seems to drop very slowly from there. I also hear a click from the other fuel relay (mounted to the same bracket) and a load click, almost like a bad starter would, coming from the intake tuning valve. The fuel pump was replaced by the previous owner, so he says. Unknown brand. Had a friend hook up a Modus and all components seem to be working properly. Could a dirty intake manifold cause such drastic performance decline? It has quite a bit of carbon buildup. I removed the Intake Tuning Valve and looked. Can I clean the intake good enough without removing the manifold?
Any ideas would be appreciated. Running out of disposable cash, never had any to start with. Kid is killing me! Please help

 

Have you checked the EGR valve for carbon deposits? The pintle in the valve can hang up and cause a massive vacuum leak. Remove the EGR valve and check the valve and passage for carbon build-up. You might also want to install a screened EGR gasket to prevent the problem from recurring.

 

I had a similar problem...and I know you did this....but did not see the mention of replacing the Fuel Filter!

 

Sounds like an EGR sticking open. Remove it and clean it out with cleaner and pipe cleaners. Make sure you to the hole on the intake too.

The intake where the tuning valve is SHOULD be dirty as hell. That's black cause of EGR feedback. If its clean you have a fuel leak, black is tickity-boo

 

I also have a 93' S10 Blazer, 4.3 Vortec, 4x4, Vin. W. I sorta had the same problems. After doiing just about everything you've mentioned I ended up putting in an AC Delco fuel pump and sending unit and then finding out it was the fuel pressure regulator. I put in a whole new spider injector unit which has a the fuel pressure reg in it and everythings peachy now. There's a great video on YouTube that shows you how to replace it.

 

I'm new to the forum, so not sure how to respond to ideas. Thanks to those that replied to my issue with possible solutions and sorry for a late response (working 7 days). I decided to remove the upper intake and found more carbon buildup than I've ever seen. Going to remove the intake manifold and glass bead everything clean. I'll post the results when I'm done.

 

Whoa whoa whoa - the carbon is SUPPOSED to be there. What you are looking for is WASHING GOLD of all the carbon.

You want to clean out the port where the EGR feeds into very well. I guess cleaning off all the black soot wont hurt, but just FYI it is normal for it to be there.