Engine and swap gurus ... help!

So, I have a 96 ITS GSR, OBD2a. Nothing special. IT prep head, bone stock motor, nothing removed from engine bay.

When I pulled the SS street exhaust and CAT to run a DC 4-1 JDM header and custom race exhaust, I went with a stock OBD1 GSR ECU with adapter harness. The first thing I noticed was it would hunt idle when cold between ~800RPM and ~2000RPM. Once warm, it ran fine. It would also sometimes immediately stall on cold start. Giving it a bit of gas and holding the idle high for a bit fixes this. Since the car ran fine, I didn't think anything of it. I figured the IAC or something just happened to crap out.

I recently switched to a Hondata P28 and the hunt idle is still there. Rules out the ECU I figured.

Well not quite. I put my original ECU OBD2 back today since I need to send my ECU off for some work, and what do you you know, the car started up without having to use a liberal amount of throttle and idles perfectly.

Sheesh .... HELP!


edit: clarity


Modified by SPiFF at 9:09 PM 8/26/2005

 

its the cold air idel thing. On most other cars its under the throttle boddy, on the intake manifold.

i dunno about the GSR though

 

Is there a difference between a idle thingy for obd1 vs 2? The obd2 version can't talk to odb1 ecu?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by SPiFF &raquo;</TD></TR><TR><TD CLASS="quote">Is there a difference between a idle thingy for obd1 vs 2? The obd2 version can't talk to odb1 ecu?</TD></TR></TABLE>


edit, aaa i just re-read your first post, and i guess that might be the case.

the GSR IM is the red headed step child of the B series.

 

I had comparable trouble with my obd2a b18b into a obd1 civic. I changed the throttle body for a 94-96 b18b one. Idle problem went away.

 

Since when did race cars have to idle when cold

 

here is the deal. The p28 has a built in voltage regulator which is slightly different that an OBD2 p72 ecu's voltage regulators. this causes sometimes slight, sometimes severe idle surge under cold start conditions due to the cold air enrichment settings in the ecu which gets its reading from that sensor, which of course relies on voltage from the ecu for power. Hondata has a setting to adjust the voltage reading from the cold air idle valve which can solve the problem, if the p28 you have doesnt have a voltage regulator that is way out of spec (which doesnt sound like your problem). There is info on this in the hondata forums I believe...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by SPiFF &raquo;</TD></TR><TR><TD CLASS="quote"> I went with a stock OBD1 GSR ECU with adapter harness.</TD></TR></TABLE>

Can you do that in IT? I've been looking for something for our OBD2 LS but haven't found something that works according to the rules as I understand them. Please enlighten me.

 

OBDII cars do not have a FITV(fast idle thermo valve), they do cold idle all in the programming rather than a simple mechanical device. The OBDI ECU expects you to have a FITV hence the wonky cold start symptoms. Also, the Evap purge solenoid has been known to cause idle issues on OBDII-I converted cars.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by .RJ &raquo;</TD></TR><TR><TD CLASS="quote">Since when did race cars have to idle when cold </TD></TR></TABLE>

You don't know what -40 degree mean

 

If you still have you EVAP emissions on the car, that might be the problem. ON the OBD1 ECU's, the EVAP solinoid open at idle and dumps fuel vapors into the IM instead of having it open when crusieing. Just unplug it (Sits right on top and in the middle of the IM) and see what it does

 

Hmmm ... sounds like I will have to live with it.

Thanks for the replies.