Hello friends. I have a 1994 Honda del sol S. Non-VTEC, D15B7 stock engine.
I was having very low RPMs while idling after warmup. I initially messed with the idle adjusting screw but there was no discernible change. So I removed and cleaned the throttle body. Come to find out that it's a VTEC throttle body with a fast idle thermo valve on it. So I said aight, cleaned the FITV as well, put it back together, and bled the coolant.

THE ISSUE--> I started it up and got it to operating temperature, (low idle is gone) but now the idle jumps from 800rpm-1200 rpm. This jump happens only after these conditions are met: it warms up, I have accelerated even slightly, and only while idling.

I have replaced the FITV, replaced the throttle body gasket w a new one, re-bled the cooling system BUT the issue remains the same.

I tried to adjust the idle screw, but if someone has the correct procedure of how to get that reset correctly, that would be great.
Or if anybody has any insights on what it may be I would super appreciate it, thanks

 

First thing is a knowledge correction, the FITV is present on all D15B7 OBD1 motors, not just vtec ones so the Throttle Body (TB) isn't necessarily a vtec TB.

You will need an external tach like a laser tachometer to be able to properly set idle.

You warm up the car, turn off, unplug the IACV, start the car and get the car idling. Once car is running with IACV unplugged then you adjust the idle screw until your idle is in the 420 RPM range +/- 50 rpm. You can't use the tach in the car, its is not accurate enough at these rpm.

Once the idle is at 420ish then you plug in iacv (I turn off car, plug in and restart car) and run car with nothing on, no lights, no radio, no ac, no heater fan etc. Idle should be something like 650 if I recall correctly, then you switch everything on like AC, heater fan, headlights and the rpm should go up to 750ish +/-50 if I recall. I could be off on these last two numbers. Will look them up later and correct if I'm off.

Once that checks out, you shut car off and pull the 7.5amp back up fuse from the under hood fuse box for 15 seconds, replug in and start the car and let idle for 1 minute. Done.

Vacuum leaks, air in the cooling system and a bad IACV all will cause idle hunting/surges.

 

Do you think this is my problem with my car? EricTheCar Guy mentioned this in his video: I was going to try these steps you mentioned, but my car has a radiator leak, likely the water pump that I have not fixed, but rather topped off every 2 weeks. My thread is also on here with a video included of my issue. I have been reading tons of threads to try and solve my problem. I would greatly appreciate it if you could give me a little direction before I jump in and follow EricTheCar Guy's video to try and save my 99 Civic LX Auto.

Thanks in advance!

 

That video re-iterated exactly what I said.

Knowing you have a leaking cooling system, you most likely have air and will continue getting air into the system.

You have also messed with your idle control screw so now EVERYTHING is out of wack.

You will need to warm up the car to operating temperature while purging the air from the cooling system, then you will have to set idle. At that point you can then see if you still have surge/hunting issues.

 

Thank you so much! I will go through these steps and hopefully everything works out with no other issue.

 

Just updating here- the problem is fixed! Turned out to be the TPS that was misadjusted and I guess only acted up after warmup.

I did perform the idle relearn, checked for vacuum leaks, coolant bubbles but all of that checked out. So I checked specs on MAF and throttle position sensor. TPS was a bit out of adjustment. Must have happened when I was cleaning the throttle body somehow. Anyways, all good now.

Thanks for your help!