So I have my 90 Civic EX. Currently running an b18a1 with Gsr Transmission. I have AC installed on this car as well. Car runs and Idles Great with AC off. When first start it it idles around 1200rpms and drops down to around 700 to 800 when its warmed up. When the AC is on and its warm, It drops down to around 400 to 500RPM. Now My main concern is when i give the car gas and let off of it, The RPMS will drop all the way to 200 and then bounce back up to 500 and back to 200. It will doo this about 10 times and finally level out. Sometimes it wont do it at all. But for the most part its every time I stop at a red light or something. I have Changed out the IACV and the FITV Valve twice. I have also changed out the throttle body. I have Checked for Vacuum leaks and cant find any. The Dashpot diaphram and the air boost valve have both been blocked off. Rest of the vacuum lines are hooked up as shown on the rywire website for b series into EF. AC compressor is New. AC blows Ice cold when normal driving, I dont really tell any difference in power or have any other problems. I really want to get this thing so it runs right and it dont sound half retarded at every light. I was told the Civic's had a switch to idle the car up when the AC kicks on but I cant seem to find it or any info on it. So calling on the other EF gods to help me.

 

Bump I know someone knows something about this

 

There is supposed to be an idle bump with the AC on. There's a flow chart in the FSM in the AC section and I know the idle bump is covered in there. I don't remember what the procedure is though.

I have an idle bump issue in my car. The idle is supposed to get bumped up a few hundred RPM with the AC on, but mine usually the drops the idle down to 400 RPM or so with the AC on and about rattles me to death (not to mention doesn't cool worth crap with the compressor turning so slow).

I ended up having to raise my base idle speed to ensure that with the AC on it doesn't drop so low.

You said you "changed" the IACV and FITV. How do you know the units you swapped them out with were necessarily good? My buddy has a '90 hatch and has had years of frustrating idle hunting and has swapped in dozens of supposedly "good" used IACV's (along with all the cleaning write-ups) from donor cars over the years, only for the problem to reappear. He finally just ended up spending the money and buying a brand new IACV - problem completely solved.

 

I dont know, I have another IACV that I know is good so I may swap it out again.