I have a 1989 honda civic with the classic honda idle surge, and I know there are tons of forums with answers but none have helped me. The symptoms are as follows:

• Runs fine under cold conditions
• Above idle, runs great
• at warm idle, it surges from ~1500 rpm and dies down to ~700, then comes back up indefinatly.

This civic with a D15 engine was born a dpfi, but was converted to a pgmfi intake system sometime before I bought it. The conversion appeares to be done well, exept for some things like electrical tape used to insulate soldered wires. Since I dont like looking like a chump at stoplights with my poorly idling civic, I have done the following to the car to try and fix the issue:

• New TPS set to 0.5v with the throttle at idle position without the dashpot proping the throttle open.
• Cleaning the IACV, followed by just replacing it since the car was still acting up.
• Bleeding the cooling system (I dont have a proper funnel, getting one soon. I dont think this is the issue for reasons Ill explan later)
• Cleaning the throttle body
• Cleaning the idle screw.
• Checked for any codes from the ecu, there are no consistant codes. Any time I unplugged the IACV, or changed anything that threw a code, I reset the ecu before further testing.
• Looking for vacuum leaks / replacing some suspect lines out of desparation
• Cleaning the cap and rotor (newly suspected cause of issue)
• Loosening the throttle side nut (trick came from another forum, didnt work. nut has been tightedned.
• Cried about it... multiple times...

Unplugging the IACV causes the idle to steady, but it is still slightly high after doing this and turning the idle screw all the way in. This is how you set the idle according to the factory manual, but the car only goes down to ~850 rpm minimum. I took this as a sign of a vacuum leak, but furthur testing proved there to be no leaks (capped off any lines and sprayed down the intake to find no changes). There is a fast idle valve, but since the intake manafold is from an integra, it has an electric valve on the back instead of a mechanical valve like the civics. Since it has no matching plug on the car, I've just capped it off along with its matching hose nipple on the intake. Since it doesnt have a mechnical valve, there is no fast idle valve to adjust, thus it cannot be an issue which is a comon cause of this issue. The TB gasket is very hard and factory looking, but It also doesnt look like its been leaking. I have ordered a new one to be safe.

I most recently inspected the cap and rotor, because I was running out of ideas. After scraching some corrosioin off of those parts, it seemed to run completly fine for a VERY short while (~2 miles). I think this has to be the issue, but I dont see how such little corrosion could cause idling issues, so if anyone can shed light on that, I would be happy.

The first time I cleaned the cap and rotor, I also removed the throttle body and NEW IACV and cleaned both. They definitly needed it, but I don't think either would be an issue.

The valves are a little loose, but the gap is not too bad. I dont think this is an issue but it is worth mentioning. It is also a non-vtec head.

Last thing to add is that at some point the throttle stop screw has been messed with. I do not know how to properly set it, becuase the manual just says that it cannot be set other than at the factory. Is there a known way to properly set it at home? I currantly have it set to leave the throttle blade as closed as possible without it acually contacting the TB itself.

Please let me know if you have anything I can try or if you need more information to help me, as I like my cars to run right! Good luck solving one of japans most complicated puzzles.

 

I have the EXACT symptoms and have done about all that you have. Surging idle at stopights at temp. Mine is dpfi though. New tps, new iacv gasket, all new vacuum lines...My next and about only 2 moves will be a new IACV and check the dashpot for a leak.

 

Since you have the factory intake, I would try the . It didnt work for me, but it could be becuase I have an integra intake. Also, if you have a FICV, try adjusting that. To check the IACV, unplug it to see if the idle steadys. If it does, then its likely your IACV. if not, than its definatly a FICV. The dashpot I think is only used for cold starts, So if you cap off that vacuum line temporarily to find the leak that would be good. Other than that sounds like your just as lost as I am. Keep in mind I;ve owned an old civic for about 60 days and I am in no way an expert.

I like the civic btw, its a lot more cleaner than mine and the LED headlights look good. Good bulbs in stock housings is my favorit, thats what I did to my truck.
Good Luck!

 

I found the issue! Sorry about not updating this thread for weeks, but I forgot I had something here. As for the issue:

when I first got the car the IACV was stuck or the seal was bad, didn’t work. I got a new one, and it didn’t fix the issue so I did other things. Turns out, the new IACV was cast wrong and didn’t seal to the intake properly and was leaking between the two ports. I put a new O-ring on the original valve after cleaning it, and it runs like new.

Bottom line, it can be anything. And just because something is new, doesn’t mean it’s better. Never trust new parts 100%