lopezisgod

iTrader: (4)

Car starts up great higher idle... As it gets warmer it lowers and idles great at about 800 or so after another 5-10 min the idle starts to surge going from 1100 or so down to500 or slightly lower... It never stalls but does this quite often ... When I drive the car for a while come to a light it will start this surging again but won't stall if I let it sit for a while with the surging... It will even up and start to idle fine... But will do again if I let it sit...

My guess is it is either a vac leak small ( but I fig this would make idle bad all the time) second guess is a crappy o2 sensor or third something to do with feul pressure or the regulator itself .. And last a dirty throttle body or iac motor

I did some searching but I really do suck at searching ... I never seam to find what I need ....

Any help would be awsome..

Thx

crazy_hotrodder

almost always this is caused by a vaccum leak. look at your hood if you still have the factory hood it will have the vaccume line roughting on the sticker. change out all your vaccum lines it will not cost you but about $20 and it is the easiest way to fix 90% of these problems. there is a lot going on between the A.I.R., pcv, egr, in an emission system and vaccum in such a system is not always constant.

lopezisgod

iTrader: (4)

I appoligise as I forgot details. The car was an original 305 5 speed 91 z28 car with an 88 350 swap no egr no air etc. The only vacuumi have on the car is hooked up to the hvac and cruise as well as vac ball on one line off the bottom of the throttle body .... One right to the fuel pressure regulator and one directly to the map ...

All the vac lines are brand new ... I had done them when I hooked up the hvac and the cruise lines that were disconnected

If it still a vac leak it would be a gasket somewhere I'll try ether or carb cleaner to see if idle comes up....

Any other ideas??

bjankuski

A surging idle is usually caused by a lean condition. Have you checked your BLM's at idle? If it shows lean then you need Find and fix any vacuum leaks and then if it still is lean add idle fuel in closed loop by upping your VE tables at idle. If it does not show a lean condition it still could be lean but the O2 sensor may have failed and it could still be lean causing a surging idle.