So, as some of you know I bought myself a 92 HB Si a few weeks back. Its so much fun its silly, but there is an issue with starting the car in the morning.
Obviously the engine is cold, but until it warms up, it idles at 2500rpm. Furthermore, after about a minute of driving (partially, not fully warmed) the idle will fluctuate between where it normally sits and 2500rpm. In detail, I will come to a stop, and the rpm would climb to 2500 then suddenly drop to roughly 1000, then climb back up.
Now, after the engine is fully warmed up, it runs like a champ. No fluctuations in the idle, it sits right where it should, etc.
I dont think it has anything to do with the mods on the motor, but it might...so I will list them:
B16A
Skunk2 Stage 1 cams
Skunk2 Computer Upgrade
I/H/E
Tranny mods...
Any ideas guys? Should I just not worry about it, as it does drive just fine after warming up. Funny enough, the fluctuations in the idle only happen in the morning after a long sit. So, after a few hours at school, although the engine has cooled off, and is cold, the idle will just sit high until fully warmed.
Let me know what you guys think.
Thanks so much

 

so if im reading this right ... your idle goes up and down from 2500 to normal correct? if thats the case check the IACV or for a vacuum leak

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by riceburnerryan &raquo;</TD></TR><TR><TD CLASS="quote">so if im reading this right ... your idle goes up and down from 2500 to normal correct? if thats the case check the IACV or for a vacuum leak</TD></TR></TABLE>
Thats correct.
You think it may be a vacume leek if it only happens for a minute or two while warming up?

 

No one else?

 

Yeah, seen this problem before. If your engine only does it when its warming up, it may be the Fast Idle Thermo valve (FIT). The valve is locted directly under the thottle body. It could also be a vacuum leak but probally not.

 

Thanks man. I will check that one out.
Much appreciated!

 

Yes, the Fast Idle Valve will cause this problem. It uses coolant temp to determine how much more air the cold engine needs so it will have a smooth cold idle. It's not uncommon for it to go out, but before you replace it, check to see that your radiator is full, as air pockets in the cooling system will cause the valve to act that way too.