98 monte shudders and shakes when hot
 

I have 98 monte carlo z34 with the 3.8 (180k miles) and if i drive it around a while and get the engine hot, if I turn it off and start up again shortly thereafter, the car shudders and shakes. From idle to even hitting some gas it stays shaking. It starts fine, doesn't matter what gear it's in (Park, Rev, Drive) it just shudders for a minute or 2. If i leave it off long enough where it cools down more, it starts up fine and runs normal. It's been doing this for a few years, and in the winter it's never a problem because it's always cooling off enough but now summers coming so I'd like to remedy this. Also, the engine has been completely rebuilt (less than 10k miles ago), heads, pistons, rods etc. Got new plugs and wires, cleaned the EGR and injectors etc. It had this problem before engine was rebuilt and has same problem still. No codes come up either so I'm not even sure what to try.

Also, not sure if this is related or a new problem that sometimes the car will die. It used to do it periodically when taking off froma stop and when it was shifting from first to 2nd it would die, but yesterday it died just in rush hour traffic where my foot is only coming off the brake to move, so there was no shifting going on...perhaps an rpm issue? Again, no codes, just dies and then starts right back up with no problem.

yes the SE light works.

Anyone have any trouble shooting steps or ideas i can try?
thanks!

ok i was going to ask about the tune up . because some times it is usually the simple doing it and a cheap fix. if it did the same thing after the tune up and it does it after the car is at operational temp and the car is shutting off it is the cat is bad. because when it is bad it heats up and acts like a damn for water not letting air to get threw when it is hot. when you have a chance let it warm up to temp and watch the collor of the cat if it starts to look like it is glowing. or the car is about to die with in 2 minutes after start up it is the cat. and it is easy to replace if you dont mind getting under the car when the car is sitting on the jack stands.

Thanks for the tip! I currently dont have any stands but I'll try to get under there to check it out.

I have the exact same issues as this and replaced the cat with an OE cat and still have the same problem.