Engine surging and dieing

I have a 1991 chevy with a 350. It has 280+ miles and i have NEVER had a problem with this truck till now. Its all the sudden hard to start in the mornings and once started it runs right then after about 45 min. of driving it starts trying to die while sitting at stop lights or in park. When you try and come out of park into drive or reverse it will die. We have replaced the wires,plugs,o2 sensor, entire distr. ign coil rebuilt the throttle body changed the fuel filter!! The fuel pump pressure has been tested twice. And pulls no codes. What else is there? Can anyone help?? :banghead:

I would check the egr valve, iac valve and make sure the timing isn't too far off 0 degrees.

hard to start cold, coolant temp sensor by the thermostat, unplug it when cold and then try to start.if it starts up ok then you know.

Thanks guys, Ill try that and if nothing guess its time to retire the poor thing LOL

wouldnt it pull codes if it was the egr or iac? I dunno im dumb founded by this!

I'm having a similar problem and was told to turn the ignition on (30 sec) to set the IAC "fully extended" then unplug the IAC and start the engine, that removes the IAC. First check the timing.

I would check the egr valve, iac valve and make sure the timing isn't too far off 0 degrees.
Which wire are you supposed to disconnect before checking the timing?

I would think that it should send a code out if the egr or the iac valve was bad. If you put suction on the egr valve's vacuum hose while car is idleing it should make your car hesitate and maybe even die if it is still working.

The EST wire is under the relay cover on the passenger side firewall. It is a tan wire with a black stripe. On 95 models and some 94's it might be under the dash on the passenger side.

The EST wire, what is EST, anyway is that the one to disconnect on a 1989 5.0L truck?

it means (electronic spark timing). On an 89 it should be under the relay cover.