I've observed this problem for the last couple months. Whatever the problem, it isn't observable at all when I'm not using the A/C. FYI just to cover my bases, I warmed the motor up and double checked my base idle and ignition timing (it was off. Thanks, expert Honda mechanics).
Here's what I've found.
1. The engine's idle speed is spot on when setting the base idle and after it's set. I also checked for any variances in RPM when load was applied per the 1991 service manual, page 11-86. When doing load checks, turning on the AC is one of them. I saw no change in idle speed. Note: trans is in park this whole time.
2. If I go driving around and turn the AC on, once the car goes through the gears and I come to a stop, my idle is raised to about 1100 or so, enough to be noticeable. If I leave it in drive and turn the AC off, the idle will drop back to normal after a second or two. If I leave the AC on while stopped and put the transmission back in park, the idle will start to bounce up to about 2k RPM, drop, and go up and down continuously until I turn the AC off. As soon as I turn it back on, everything seems normal. I've verified this behavior many times.
3. After the motor was warm, I did make sure to check the FITV and gently bottomed it out/tightened down. I think this is the correct way to verify it's adjusted correctly, not 100% sure since Honda just says to check the o-rings and replace otherwise. I'm planning on checking the airflow when it's cold and hot.
As I don't have the special Honda test harness, I'm not sure how I could go about checking the items on page 11-69. I will say I haven't noticed any other malfunctions or idiot lights on the dash indicating problems.
I'm going to report back later after I've checked the FITV, but I'm not confident it's the problem. I have a new Honda one ready if it is though.
Anyone ever experienced this?
Here's what I've found.
1. The engine's idle speed is spot on when setting the base idle and after it's set. I also checked for any variances in RPM when load was applied per the 1991 service manual, page 11-86. When doing load checks, turning on the AC is one of them. I saw no change in idle speed. Note: trans is in park this whole time.
2. If I go driving around and turn the AC on, once the car goes through the gears and I come to a stop, my idle is raised to about 1100 or so, enough to be noticeable. If I leave it in drive and turn the AC off, the idle will drop back to normal after a second or two. If I leave the AC on while stopped and put the transmission back in park, the idle will start to bounce up to about 2k RPM, drop, and go up and down continuously until I turn the AC off. As soon as I turn it back on, everything seems normal. I've verified this behavior many times.
3. After the motor was warm, I did make sure to check the FITV and gently bottomed it out/tightened down. I think this is the correct way to verify it's adjusted correctly, not 100% sure since Honda just says to check the o-rings and replace otherwise. I'm planning on checking the airflow when it's cold and hot.
As I don't have the special Honda test harness, I'm not sure how I could go about checking the items on page 11-69. I will say I haven't noticed any other malfunctions or idiot lights on the dash indicating problems.
I'm going to report back later after I've checked the FITV, but I'm not confident it's the problem. I have a new Honda one ready if it is though.
Anyone ever experienced this?
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