I've done my "due diligence"; I've searched the net and this forum but everything I can find for this symptom seems to be talking about Throttle Body injection whereas my '86 had Multi-port injection.

When I start the engine when it's cold - ie after sitting overnight - the idle will "surge" for a while, swinging back and forth between about 2000 RPM and almost stalling. After anywhere from 10 or 15 seconds to occasionally as long as a minute or so, It'll settle down and then it's completely fine until I let it sit overnight again.

I never check a check engine light, and no codes are stored in the OBD-I.

I'm not sure about your particular engine, but most have some accomodation for cold starts. It sounds like you probably have a bad sensor (or electronic valve), most likely it's attached to your throttle body.




Built 94-97 head for sale: http://www.j-body.org/classifieds/engine/47069/

Oops, I meant to say that I never get a check engine light, not that I never check it.

Umm there are several conditions that could cause the idle issue cold.Could be plugs.wires, hei ignition coil but I would check the tps first with a multimeter to make sure (while cold) not running key on and check the readings.IF u do not know how check out this site http://www.wellsmfg.net this has good info in diagnostics on the how to check and it's pretty easy.It could be the egr valve sticking and needs to be removed and clean the carbon out of it as well.I realize its not setting a code or even a intermittent code which is not uncommon in our first gens(know from exper).Scroll down to 1998 volume 1 tps is knowledge is what u should look at.Try the basics first like wires,plugs check all the vac lines and the egr and if the coil,ignition is way old may be a poss too.But the tps or even the IAC idle air control may be sticking and may not set a code but,cause the idle to go all over the place.That's my recomm at this time.

I thought on this after I posted last wk and would lean more towards the egr valve sticking.Bc it functions based on engine temperature and it will affect the idle greatly.I know I suggested several things and even the part in mind.I would def start there first if it has never been removed I would highly suggest it for sure.There are several versions of the part mine has a round metal shape with a moving pintal that moves up and down with one vac line,while urs may be different it will have a diaphram inside that opens and closes vacumm and if it has the pintal make sure it moves freely up and down,a quick check to see (engine cold) is disconnect the vac assumming it has one and see if it changes the idle on cold starts.IF it does remove look at it clean it and reinstall and chk again cold and if no change replace the egr.The diaphram is what wears out from age being its rubber cracking etc.IF the above is not the case start on the other items I posted on checks.