hesitation / idle issues

[Jeff B]

So my 300 has a weird idle / hesitation issue.
When it is cold outside in the AM (like 50 or less) it idles pretty bad, and has died on me once (when I got to the end of my block and pushed the clutch in)
Also, when I am under partial throttle, it just seems like it is being "held back" for lack of a better term.
Now, once it is warm, and I am in the upper RPMs (over 3-4k) and I floor it, it seems to run fine.
any one of those (heat, or high RPMs, or full throttle) make it better. But full throttle alone at LOW RPMs (under 2k) is still pretty bad. Idles pretty good when warm, especially if it is warm outside. But it still has that partial throttle hesitation.
Only mods are a Z1 intake, which I checked and it is mounted tight with no apparent leaks. Also, dont see any leaks around the rest of the intake system. I have checked the TPS as well.
Seems like it could be a vacuum leak somewhere, but as I am new to Z cars I am not sure.
Doesnt seem like it could be a plug or injector, since it runs strong under other conditions.
Anybody else have any ideas?

[marty1mc]

Pull codes first, then check for corrosion on your connectors (CAS, PTU, injectors, idle circuit, coil packs).

[es.biggs]

Might want to try checking your timing after that

[GerryO]

http://home.swipnet.se/e-solutions/IdleTech.html

http://home.swipnet.se/e-solutions/IdleTech2.html

On a car this age, pulling the plenum to really get to everything can be a very good thing to do. You might want to replace injectors too while you are in/under there and if they are original. A bad injector (coil/electrically) should trigger the CEL. Check the EGR valve too.

[Jeff B]

Pulled codes, got left o2 sensor and knock sensor. Reset ECU, then ran codes again (still got left o2 sensor) ran the o2 sensor check and the left looks bad. Moved connector around and cleaned etc but no change (light stays off, only blinked once ever)
Bought a bosch replacement, but whats the easiest way to get to that thing? I have an o2 socket, but just cant get to the sensor (exhaust is still pretty warm now so I am letting it cool)

[Jeff B]

got a bosch replacement, the one without the connector. I am good at wiring so thats no biggie. Got the old one out (with the o2 socket, 3/8 universal joint, 18" extension, 1/2 to 3/8 adaptor, and a 2 ft 1/2 breaker bar)
was about to wire up the new one to the factory connector, and noticed the new one has smaller threads than the one I took out. Took it back and they ordered a direct fit.
Is there a difference between 1990-1995? I know 1996 went OBD2, but they list the same part for 1989-1995 at least (thats all we checked)
What do you guys use for replacement o2 sensors?