Closed Loop Issues

[Kenny]

Hey guys. Just picked up a 99 tahoe OBS for pretty cheap. But it needs some work. The main issue i'm trying to tackle a closed loop issue that comes up once its warm. Truck starts right up with no hesitation. Once it warms up and hits closed loop. It idles poorly and misfires to the point it almost dies. Fuel trims go thru the roof and then suddenly all is well again as it kicks itself back into open loop. Ive cleaned the maf sensor,map sensor,and iat sensor. After cleaning the maf it seemed to run better for around 30 min and started doing it again the next day. Spark plugs were replaced, wires,cap and rotor. I checked for vac leaks to no avail. Not quite sure where else to go. Helpp

 

[SunlitComet]

get your hands on a scanner that can proprietary gm data so we can see the data from sensors like the maf and o2 waveform among others. also have you tried a iac reset or wiped out the battery stored data from pcm by means of battery disconnect for a minute. check your o2 harnesses as well for tampering or damage.

 

[Kenny]

I dont think i can get a scanner like that. I have a cheapy actron that can read the lb/m on the maf, iat, and 02 sensor voltage. None of the 02s seem to hit over .5 volts though they do fluctuate a little

 

[SunlitComet]

what is the reading on maf when at idle? which o2 fluctuate and how much?