I bought a 91 Civic DX on Marketplace about 3 months ago. The past 3 weeks I noticed a slight rough idle sound. Nothing serious but sounds like a small surge. As the DX model didn’t come with a Tachometer I can’t actually see the RPMs and I’m just going off of what I can hear. It will pop up about a minute into idling and is present anytime when in idle, whether it be a cold start or after driving a bit.

I did a small amount or research and have cleaned the IAC valve as well as cleaned the throttle body to no avail. A couple days ago I was giving my buddy a lesson on stick and after some stalling and good times, the surge became louder than ever before.

This is my first post on Honda Tech so I’m still figuring out how this works, I can provide more information if needed.

Any suggestions? All help is appreciated.

 

Could be a number of things. You could try getting a scribe or a thin marker and marking the position of the distributor, and then loosen the 3 bolts that hold it in and try advancing or retarding the ignition timing just a bit to see if the idle levels out (do this while the car is running). As long as you mark it before hand there isn't much risk in trying this because you can always put it back. If the issue persists you could try replacing the ignition module (not the ignition coil) inside the distributor. You can get one for $40~ on rockauto or amazon and they're a pretty common problem on this generation of civic. It could also be a fuel related issue. You could try replacing the fuel filter, a clogged fuel filter could cause a lack of fuel to the injectors causing it to surge, or even pouring some fuel system cleaner in the gas tank could clean out the injectors if they have a blockage of some sort. Best of Luck!

 

Thank you so much for the response, will definitely try all of these.

As for an update on the idle surge, it has since grown faster and louder but still doesn’t seem to affect driving and just annoys the crap out of me haha. I also seem to have slightly worse gas mileage however I may just be in my own head trying to find symptoms and solutions.

Since my first post I have done more research and have some more knowledge on the issue and have compiled a list of possible solutions.

Here are all the things that I have now done and have not fixed the issue.

-Cleaned MAP sensor
-Cleaned IACV
-Cleaned Throttle Body
-Replaced Spark plugs
-Checked Air Filter
-Replaced Valve Cover gasket
-Flushed and Bled Coolant System
-Did a *brief* check for damaged hoses/clamps that may be causing a vacuum leak

The next things in my list to do are going to be to:

-Check TPS Sensor
-Check Fuel Filter
-Check Fuel Pump Relay
-Do a more detailed search of hoses to find a vacuum leak.
-Tonight I plan on checking the spark plug wires although I doubt they are the issue it won’t take long at all so I might as well

And I will now add your suggestions to the list.

 

Yeah if you've done all that then it would definitely be worth checking your ignition timing with a timing light, it could be that your timing belt slipped just a tooth of 2. Mine had a decent surge at idle once the engine warmed up because i had installed the timing belt 1 tooth off and never reset my distributor timing. Once I fixed it and adjusted the distributor it ran great, it kinda sounds like you have a similar problem

 

Update Number 2:

Sorry for the few and far between responses, life gets in the way haha.

I did go ahead and retime the distributor as you describe with a timing light. Unfortunately no dice.

I still have a number for things to try so I’m not completely lost at the moment, just need to find the time to do them.

Whats left to try is this

-Replace TPS sensor
-Replace fuel filter
​​​​​​-Try fuel system cleaner as you mentioned

The list is thinning and my worry is growing but like I said I’m not completely lost yet.

As for the distributor, a new one was put in just before I bought the car so I don’t have much concern about the ignition module, however it was apparent that when it was replaced it was just slapped in and not timed, so I guess timing it was still beneficial.

Recently the car has been idling low at stop signs and red lights, has never died on me and I don’t think it will but now I’m getting into the area where this issue may be effecting driving.

I appreciate your responses, and beg anyone who may have a solution to tap in.

Thank you!

 

When you changed the fuel filter did a bunch of rust or orange/brown colored stuff come out? could be rust in the tank from sitting. My 91 civic Hatch was idling rough and would start to run rough and occasionally stall when decelerating especially when it got at or below half a tank. I chased a bunch of issues all of which helped in small increments but the fuel tank was in bad shape due to rust on the inside and clogged the fuel sock and wore the pump. I also had a high idle speed issue when sitting in traffic. turns out the throttle cable was just a bit too tight and when it warmed up the tube would strech and raise the idle speed to around 2000 rpm. I just loosened the cable up until the issue stopped. It is alot looser than I would like to see it but thus far no issues and the idle is rock solid.

 

This video was really helpul for an idle issue that just came up for me, maybe it's the same issue