1200rpm idle when hot (and other issues)

[Varinn]

Trying to figure this out but dont have much time to look at it. 1990 325i manual with full engine reseal and all new vac hoses.

Cold starts fine, idles at around 700rpm
Warm starts hard (cranks for about 5 seconds before ignition), idle at 900
Hot start fine but idle at around 1200-1400rpm.
400KM on 55L of fuel with 50/50 city/highway (65L tank)
91 octane and chipped (same issue before and after)
Stock exhaust
3.73 open diff
Unknown o2 sensor age
New fuel pump and FPR, original injectors

I know vacuum leaks are an obvious thing to check, what else? ICV seems to be working (buzzes), code 1444 on stomp test, passed emissions easily after engine install, I could replace o2 sensor as it may be worn out but not sure if I should go mustang sensor or oem bosch. Car never stalls or runs rough at idle (except on first 5-10 seconds after cold start in winter), always starts fine when hot but idles high. However after letting the engine cool for 20-40 minutes attempting to restart takes a bit of effort. Cranks fine but does not catch for 5-10 seconds. Wait over 40 minutes and it starts fine, wait under 20 and it starts fine.

Suggestions?

[jlevie]

My recommendations are to replace the O2 sensor (I use OE parts) then have a smoke test run and fix the leaks it reveals.

[Varinn]

Thats kinda what I was thinking. Should I do the o2 sensor before or after vac inspection? What reasons do you have for going oem and not saving money on the r3v interwebs magic mustang solution? I'm assuming the potential of shitty wire connections could change resistance and as a result, performance?

[jlevie]

It doesn't matter which you do first, as long as both are done.

[Varinn]

I'll be picking up a new oxygen sensor tomorrow morning, hopefully to be installed on the weekend. I'm also going to grab a can of carb cleaner and very very carefully try a bit of spraying around the engine bay while it's running and idling high. If I can't find the vacuum leak this way, I guess the best method is to find a shop capable of doing a proper smoke test?