I had to replace the fuel pump in my wife’s 1994 Ply Voyager. Everything started right up when I was done, but as soon as I let off the gas so it could idol it would die. Never had this problem before in any other car I’ve had. I’ve check and replaced all vacuum hoses thinking that was the problem and got the same result. Why would the dang thing stay running?
The IAC valve may be faulty and/or the throttle body needs cleaning.
Have you tried doing a fuel pressure test? You need the specs for that engine when you do that or you may get lucky and someone here may have the info.
Do you want a list of likely parts to change? OK. Use a throttle body spray cleaner to clean the IAC valve air passages, and the throttle body bore, and throttle plate.