Here is my problem:

Vehicle is a 1988 Chevy 1/2 ton Silverado 4x4.
Engine: 1996 Vortec 350 longblock, 15K miles
Intake: Edelbrock Vortec Performer, with Holley TBI adapter plate
Stock internals, only aftermarket addition is the intake manifold and adapter plate.

No vacuum leaks, been over that with a fine tooth comb.....none exist.
When warm, the idle hunts all over the place. Usually varies between 1200 and 1500 rpm. At operating temp, the truck runs great, has a slight stumble just off idle, but pulls strong.

When cold, the idle stays low.....maybe 400-600 rpm. You cannot just give it throttle, you have to "baby" it and gently feather the throttle until you get up to speed. Idle and part throttle are really really rough.
Once the temp gauge reads 180, the engine just smooths out and runs fine.
Codes that have been set:
EGR (which I expect and will live with, as the Vortec has no internal EGR)
TPS
MAP
O2 sensor
ignition control module

All sensors and modules were replaced with new ones when I did the engine swap.
Also, last but certainly not least, I set the timing with the engine fully warmed up, but setting the timing at anywhere from 0-6 degrees advanced makes the truck sluggish, and listening to the engine, the timing is way retarded.......you can hear the exhaust and tell the engine wants more timing.
Startup takes about 5-6 seconds of cranking then the engine fires up and runs.
Idle vacuum is 15 inches, I think it should be higher, but I've never seen anyone post what their idle vacuum readings are.
I'm scratching my head with this one. I don't mind spending more money to get it fixed, as I'm not one to let a problem defeat me.
On the topic of ignition control modules, I have a collection of them, all new or with less than a thousand miles on them...none showed any improvement in the way the truck runs.

The truck has a lot of miles on it, not sure exactly how many.....odometer is stopped at 91K. I replaced the fuel filter when I bought the truck. Fuel pump is stock as far as I know.

I know this is primarily an F-body site, but from reading here for almost a year, I know there are some real TBI experts who frequent this website and I want to know what they think my next step should be.

Thanks in advance.

 

Sounds like it is not getting enough gas. Find a way to give it more and see if it helps.

 

No one else has any suggestions or comments?

I'm contemplating installing a new pump and an AFPR soon, just because I do a lot of driving on the highway with my job.

 

Are you still having this problem? If not let us know how you fixed it.

 

It's your calibration. You have a couple options. One is to live with it because no amount of replacing hardware will fix your problem. Or you can get a 96 vortec CPI intake, dizzy, trans, w/computer and be all good. OR you can burn your own eproms to disable EGR, fix your idle, fix your light throttle accel, fix your delayed power enrichment, fix your tip in bog (it's lean, just trust me on this), and fix much much more. That of course will cost you $180 for everything you need. The only problem with that last option is that it takes time and patience. Although the first few chips will be leaps and bounds better than stock. Oh, one last option, go carb. Truthfully, carb is great for people that can't stand using computers. If you like the idea of simply "recurving" your dizzy and fuel map without having to pop the hood then do yourself a favor and start burning your own eproms. It's really easy, just do a search and you'll see why I'm so pushy about this option. The only things you need to buy are extra 2732a eproms, a burner like the xtronics pocket programmer, and an eprom UV eraser. The tuning software is all free .