Surging idle on 99 SI

Like it says I have a 99 Civic SI that has a surging idle. When the car is stopped, after driving it for a while and it's warmed up, the idle will surge. First it surges from 1000-2000 rpm for 3 to 4 cycles, then from 1000-1500 rpm for another 3 to 4 cycles, it then settles at 1100 rpm or so. I will list what is done to the car, and then what I have checked for. It has a DC 4-2-1 header, AEM air intake, AEM fuel rail, B&M fpr and gauge, CTR cams, Flowmaster exhaust, JG Edelbrock 65mm throttle body and an AEBS intake manifold. The TB and IM were just recently installed, which is when the problem started. I have checked all vacum leaks, the vacum lines, coolant lines, TB, IM, TPS, mass air and IACV, there were no leaks to be found. We adjusted the main idle screw, that didn't help. We checked the TPS's voltage, adjusted it, that didn't work. I have reset the ECU numerous times, usually every time after we adjusted something. There is plenty of coolant in the car, and no air in the lines. The IACV is fairly new, but it was put on before the TB and IM were. The only thing I know of I need to check is the screw under the throttle plate and hope that works. I would still like some input from you guys if you have any other ideas on what else it could be. Please help! :banghead:

I have the same exact problem on my 93 Civic EX. People keep saying its a vacuum leak. There's no leaks. I wish I could get mine fixed.

I want to try the idle screw thing but I was told not to mess with it.

Can you walk me thru on what ur supposed to do exactly with the idle screw to try and fix it?

It could be the fact that tou upgraded the fuel delivery system without upgrading the fuel pump. if the pump is not supplying enough fuel the car is trying to "Feed" through a straw. like a mcdonalds milkshake the thottle body is choking trying to uck it through the fuel line.

Ive got the same problem, but ive got a 97 b16swap w. 11:0:1 compression forged rods, and pistons, full valve train p&p head and p&p intake manifold. after the internals were changed problem got worse, my car would acualy die, in its idle cycle. I got a new ECU, my car doesnt Die anymore, but the idle still kinda jumps around.

Someone mentioned to me that it might be my 02 sensor that had gone bad, or is going bad.

Other than that Im clueless

I have the same problem with my 95 si, but I already posted a thread. I also had people telling me it was a vacuum leak but I can't find anything. The same goes for an O2 sensor, but I have no clue.

This weekend I replaced the IACV to see if that was the problem, but it wasn't. I noticed, however, that my Air/Fuel gauge was either not working or it was acting really strange, this leads me to believe that it might be my O2 sensor as well. Luckily we have a good shop, that comes highly recommended from some people who have either helped me with this or thought of some things that might solve it, in town. They will do checks for people who have modified cars and are having problems with them. One of them is a highly trained Honda tech, and is also trained in the Hondata system. I have been told that on the early Civic SI models the OBD2 ecu's have had problems and need to be replaced. I am going to convert to a P28 complete with the wiring harness and Mugen chipped and hope that it will help the car out, maybe even get the power out of the car that it should have with all the bolt ons that I have. I will drop it off tomorrow and get it back on Friday to have it just looked at: compression check, air/fuel check etc..I will be putting the new ECU in it either at the same time or maybe this weekend, but as late as next week. I will keep you informed on what caused the problem and what it took to fix.

I would just like to point out that a P28 ECU is an OBD1 ECU. Everything that I've read online has said that. I don't know tho if that will work w/ your engine or not.

But here is a link to some honda ECU tech data.
http://www.hondata.com/ecus.html

Could be an idle control valve that is bad. But first I would check the easiest thing: spark plugs.

could be your timing

Problem fixed! It was the main idle screw and the screw under the throttle plate, they just needed to be adjusted to where they are supposed to be. :69bronco: the P28 is an OBD1 ECU, but they make an adapter wiring harness that converts your OBD2 to an OBD1, you can get the setup from Hondata. This is the only way that you can get a chip or a program on your ODD2 ecu controlled vehicles. It is really worth the money when you consider that with the OBD1 you have endless things that you can do to it. However, the advantage with OBD2 ecu is that it is alot more forgiving when aftermarket parts are installed on the vehicle, provided that they are installe correctly and tuned correctly as well, otherwise you end up in a similar situation that I did, but now I have no check engine light and the car idles great with no surging at all!

rock n' roll...thats awesome for me if i do an engine swap!!!