I'm trying to help a friend with his idle surging problem. He has a 93 del sol si with 99 B16A2 swap using 95 GSR wire harness...with P30 JDM ecu. Cold start..the engine would rev up and down between 2k and 1k. After it's warm up...it would go down to 800 rpm. The weird thing is...once in awhile it would surge up and down.
Replaced the iac..and the problem wouldn't go away. Another weird thing is..when I unplugged the IAC plug...the engine would shut off.....When leave it off..the engine wouldn't start up. What could it be? Normally...doing this would cause the idle to be lower and not shut off the engine. Any thought guys? Thanks.

 

Vacuum leaks? You check the PCV valve?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TimoneX &raquo;</TD></TR><TR><TD CLASS="quote">Vacuum leaks? You check the PCV valve?</TD></TR></TABLE>

if it's vacuum leak...the surge will be there constantly. This happens at start up...and sometimes...at the lights. really weird.

 

My JDM B16A is doing the exact same thing. I thought it was due to a leak in my catch-can, I fixed it, however it was not the problem. It would not be the PCV valve because technical the PCV valve is only open at normal operating temp, or when oil vapors are maxed out. I was going to replace the IAC, but I think I might clean it first. From what you said that you've replaced it and it didn't solve the problem. Damn.

I reset my ECU, did not fix it, actually seemed to make it worst. When I drop engine into neutral, my RPMs drop to idle, then bounce once to 2K. Does this all the time, is this what your friends see as well?

 

I would look for(in this order):
*vac leak(doesn't soun like a vac leak, since it doesn't happen all the time)
*air in your cooling system(this can cause the IACV to go nuts when the pockets of air hit it and it can't keep the idle constant)
*bad IACV(most of the time, when people thinkt hey have a bad IACV, it's one of the situations above - vac leak, or air in the cooling system)

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by inspyral &raquo;</TD></TR><TR><TD CLASS="quote">I would look for(in this order):
*vac leak(doesn't soun like a vac leak, since it doesn't happen all the time)
*air in your cooling system(this can cause the IACV to go nuts when the pockets of air hit it and it can't keep the idle constant)
*bad IACV(most of the time, when people thinkt hey have a bad IACV, it's one of the situations above - vac leak, or air in the cooling system)</TD></TR></TABLE>

Yeah, good call, even low coolent will give that crazy idle during warmup...