I recently swapped a D15B8 into my 1990 Civic Si and everything seemed to turn out great and the car was running really good until I replaced the header this weekend. The original header was really rusty and I think it was leaking so I bought another one and swapped it out this weekend. The car was running great before this but after I did this the car started idling weird. It will run fine for a few minutes but after it gets warmed up the idle will bounce around from about 800 to 1400.

I’m not sure why the idle would be messing up since I only swapped out the header and didn’t touch anything else. The only things I have tried so far is resetting the ECU and swapping out the O2 sensor with another one. Why would just swapping out the header cause this problem?

I know there are a few post about this but I’m kind of new to cars and don’t know what the terms mean and was wondering what would have caused this problem and what could be done to prevent it from happening again.

 

instead of starting another thread i will reply to this one. to show that i'm searching. i just did a head gasket on my 1990 civic with a 98 civic motor. and when it warms up the idle surges and i can't figure out why i checked grounds. and vacum lines. any help would be great.

 

sounds like an idle air control valve.

 

that's what i'm looking into right now. now if there was a air pocket would that make it now work right considering there's colant hoses coming from it?

 

there should be a 12mm bolt on the upper radiator hose that you can loosen to bleed it off a lil. but i doubt that would help much, might as well try though

 

https://honda-tech.com/zero...age=1