Rough idle

[Dylan88]

Recently got a 91 Chevy going after sitting for few years. Did the fuel pump, o2 sensor . When cold start it idle really rough and goes up and down and almost dies. Then driving seems rough till its warm then drives pretty good. Any ideas

 

[Glocker21]

Try MAP sensor. My new to me 1990 is just shy of 200,000miles and I did that and it helped

 

[PlayingWithTBI]

Instead of throwing parts at it, get a scanner and look at the data stream to see what's going on. It could be TPS, CTS, ICM, MAP, EST, and a multitude of other TLAs (Three Letter Acronyms)

How's you fuel pressure? Is you timing set correctly with the EST bypass wire disconnected? Bad fuel from sitting? Dirty fuel filer? Are the injectors spraying an even cone? Ignition coil or pickup coil inside the dizzy? Plugs, wires, cap and rotor?

 

[Schurkey]

Why are you starting a new thread on the same problem you already got answers on in your previous thread?

https://www.gmt400.com/threads/fuel-pump.53519/page-3

And in this thread, you forgot to mention that you've got an undiagnosed/unrepaired Code 42 that might be the root cause.