Hey there guys, I was hoping someone could help me out with a problem I've been having on my 2000 honda civic si, the car surges on 5-10% throttle but idles fine.
After doing some research I went through and checked for vacuum leaks, bled my cooling system, tested the TPS/MAP & checked out the IACV as well. All look to be fine, nothing is disconnected or cut.

Car is throwing 2 codes for IACV & VSS (i fixed the vss already)
I tried disconnecting the IACV while the car's running and that didn't help so I then plugged the iacv holes with cardboard acting as a gasket to delete it, and that didn't help either.
I noticed it has a little more of a rough idle to it while cold, but when it warms up it idles fine. The surging only happens at about 5-10% throttle, and if I rev it above that it clears out and the car sounds fine.

My car is a LS-VTEC and is chipped with a p28 ecu. I got the car dyno tuned about a month ago and it's been running great up until this surging problem has started.

ANY help or advice on this will be greatly appreciated. Thanks in advance

 

what did it do?

 

@tony_2018
didn't make much of a difference, sounded like it dropped slightly in rpm but not by much.

 

Try cleaning out the idle air control valve

Make sure you dont have any exhaust leaks that could send the front oxygen sensor bad readings

 

RPM should drop significantly when a two-wire IACV is unplugged and doing that should throw a code 14 due to open electrical circuit. If you get code 14 immediately upon starting, check resistance of the IACV coil (about 15 ohms IIRC), and the circuit. The yellow-black wire is an ignition live wire, the ECU pulls the other wire to ground. Make sure the proper harness plug is plugged into the IACV.

 

My 2 wire IACV plug is actually solid GRN and Black, I just dont understand why it ran fine on the dyno and all of a sudden I get this, no changes have been made to the car other than swapping out different map sensors and tps sensors.

I also checked for resistance on the IACV and got 11.7, seems alright to me. I also pulled the plug again while the car was warming up today and surprisingly saw no difference in the idle.

I would also like to note this car is converted from obd2 to obd1 with a jumper harness, therefore I cannot check my check engine lights without having the engine off and one of these blue plugs jumped to check my code.

This is my daily driver so again any help is greatly appreciated. Thanks everyone

 

Get the codes

Clean the idle air control motor

Unplug the primary front oxygen sensor and drive with it unplugged to see if that gets rid of the problem

 

I actually just cleaned it pretty well and did see some improvements but quite not what i wanted so:

Fired the car up, the surging stopped after i cleaned iacv so i let it warm up to operating temp, took it down the road and as I start getting up in rpm I notice it starts to surge pretty bad in the higher rpm now... I would guess 10-15% throttle, and again car idles fine and revs fine.

I also do not have a oxygen sensor i have an AEM Wideband. Bought it new a few months ago so my problem shouldn’t be related to that.

Im gonna take a run to the local junkyard and try to find a clean iacv and hope that this solves my issues.

 

The plug with the green wire and black wire is actually the PS pressure switch. I suspect you have some plugs mixed up. The wire colors for your IACV plug are blue/black (black/blue) and yellow/black (black/yellow). This is assuming that all wiring in the engine bay is original and has not been modified. If someone has added or replaced a plug... you never know what might have been used, so you would have to follow the wires back to the repaired/taped up/soldered area and see if this leads you to the proper colors I mentioned above.

 

Thanks for the responce JRCivic1, I ended up grabbing a used IACV from a crv at the junkyard yesterday. Cleaned it up pretty well and saw some improvements at first, but after about a minute or 2 of driving the surging comes back so I'm gonna trace my wire colors back and make sure I'm dealing with the correct plug here. I will post updates as I go on this.

Thanks again and Happy holidays.

 

If the surging comes and goes, it is likely an air bubble in the cooling system which needs to be bled out and not a wiring/mechanical issue. A wiring problem will not come and go... the issue will remain steady.

 

If code 14 is being thrown there's an electrical issue.

After resolving that you need to set up the idle by unplugging the IACV and adjust the air screw (or otherwise undo whatever the previous guy did to make it idle faster without a working IACV) to get down to 450 rpm. Then plug in the IACV and it should come up to 750 and run steady.