VTEC Civic 94 EX Coupe
Any help appreciated.
Facts
1. Morning times the car start perfectly, RPM go to 1300 rpm and in 3-5 minutes rpm reach around 600 rpm, good and steady, for a while.
2. Once engine reach working temperature, the rpm sometimes go down almost the engine stalls and jump back to 600 RPM..it is not steady all the times. I have noticed that as well when Im driving and I have to stop in a traffic light, the rpm go down and restored
3. Sometimes without the AC and rpm are very low, that engine almost stop.
4. Sometimes I think that ambient temperature has something to do with this situation.

Actions taken.
1. Change the IAC valve and nothing improved
2. Tight up the idle adjusting screw and the rpm go much more down, but that is ok (yes I disconnected the IACV prior to and remove backup fuse to erase any map)
3. If I un-tight the screw rpm does not go above maybe 500 rpm. I almost remove the screw and form the middle position to the almost end or out position, RPM remains the same. And does not had any increase on RPM by turning the IAS

What should I do?
Sensors, Defective Throttle Body? Vacuum Leaks.

regrds
javier

 

possibly a vacuum leak, but a quick thing to check is the ignition timing, it can cause havoc with the idle as well.