96 LS. Problem started with surge between 25-30 at cold start, settled into a solid idle when warm. Got CEL p0505 last week and the next day it started surging at idle. Cleaned IACV, replaced o ring gasket, reset ecu, checked for vacuum leaks, no change. Replaced IACV this morning with a brand new unit, no change. Running out of ideas, searched my *** off, need some help. Thanks guys.

 

Okay so I made something happen... unplugged the connector on the iacv, spun the throttle adj screw all the way to the right, reset ecu, started car. Now it's idling around 1400 with no surge... going to let it run for a bit to see if the ecu can learn and then try and turn it down to a normal idle.

 

touch the gas and it goes back to surging.

 

If the engine only surges when warming up its probably your fast idle thermo valve (FITV). Its mounted under your throttel body, remove and clean it up. should take care of the problem.

 

Car is a 96 though and it's surging all the time now.

 

Oh sorry. when you unpluged the iacv did the idle drop?

 

No, it settles at around 1500 but it doesn't sound quite right. I have suction on the upper port in the tb too.

 

if you plug the upper port in the tb with your finger, does the idle drop?

 

No, but there is suction. Does that suggest a vacuum leak somewhere that I didn't find? Also, when I plug the lower port just so I can get the idle steady and if I plug it completely the car dies. What could that mean?

 

You got a vacuum leak there. Plug both holes in the throttle body, or plug the whole throttle with your hand. If the engine doesn't die, there is deff a vac leak. The only way it should receive air is through IACV and FITV. Keep that in mind and you'll fix it.
Good luck!

 

Kind of a bizzare situation I found myself but it's been resolved. The engine must have been swapped from an automatic LS because all the stampings indicate 96 but it does have a FITV. Car was back together and running perfectly inside of an hour. That plastic screw thing in the fitv was completely backed out so that would explain why i wasn't getting any codes. Another interesting note, the TPS was showing up on the scan tool but moving the throttle didn't change the output at all. It was also getting power at the sensor so my mechanic buddy and I stood around like a couple of slapdicks and had no idea what was going on. Wish I hadn't sprung for a brand new iacv but I guess that's one thing I don't have to worry about down the road. Thanks for your input guys.