TBI rough idle and running 350.

Hi folks. I'm new to the forum and have seen several posts on this topic. My problem is driving me nuts. I have a 1993 Roadmaster wagon that has a 350 TBI. The guy I purchased it from had installed a crate engine. I purchased the wagon about a year ago and for several months it ran fine. Now it won't idle when warm and hesitates and sometimes dies. Even going down the road at a steady speed it misses.Here's a list of what two very fine mechanics have done so far.

New Cat converter
O2
IAC
coil
vacuum hoses
plugs and wires
alternator
Intake manifold gasket

These have not solved the problem. It seemed to run better when the alt was unhooked but a new alt didn't fix it.
Fuel pressure is good. I really love the car other than this. Can a GM 350 really be this complicated? Any suggestions will be greatly appreciated. Stumped in Bowling Green Kentucky.

use the KISS method.
Check fuel, Air, and Spark. depending on these checks it will lead you down the right path.

it could be a heat soak issue with the dizzy? or a fuel delivery problem, or an EGR valve issue.

First question, does it show any code's? (check engine light)
Pete

I had a problem similar. Mine would die at an idle in gear or in park or sometimes driving down the road. I also have a '93 350/TBI crate motor. A mechanic I knew put a temporary inline fuel pressure gauge on it where we could see it when we drove around and the fuel pressure would all the sudden drop real fast to 6 psi. and die. Replaced the fuel pump and problem solved. Dropping the tank wasn't as bad as you might think. Be careful of the sending unit, they're expensive. Paul

You can put the metal lines from a 91-92 FW with an LO3/5 engine, or from a 93 FW. They have Schrader valve ports, and you can measure your fuel pressure. You could also check the ground at the thermostat housing. The ground is for the computer and O2 sensor. My LO3 would stall and run rough at idle until I fixed the thermostat ground. You could have a broken wire somewhere that is making physical contact most of the time.

Thanks guys. Supposedly all the recommendations you've mentioned have been checked by my local mechanic. I'm to the point of just taking it to a Buick dealership and see if their people can track it down. In addition, with the artic blast this week, the heater won't put out warm air. The fluid level is correct. I'm gonna put the 195 thermostat in this weekend. I'll be double checking the ground at the thermo also. This forum is the greatest. Thanks for letting me join. Freezing in Kentucky.

The 195 thermostat may be an issue if the current one is a lower temp. The car will only run correctly with the 195 thermostat.

You probably need to flush the heater core to get the heat to work. Also if you have a BRW, you might want to try the climate control reset in case the calibration for the blend module is out of whack.

To be honest the stalling when warm issue sounds like a heat soak issue with the coil or Distributor. The magnets in the distributor could be cracking up causing the rough idle/miss while steady cruise issue.
Then again the miss while steady cruise could also be EGR related.

Thanks again guys. Will have to check the fuel pressure, thermo ground and dist. this weekend. My mechanic may have missed some of these in his frustration. PS how do I add photos to a post?

Great news. The problem was a bad wire on the ground at the thermo housing. Thanks for all your suggestions. Again, a great site.