my 96 lt4 has developed a bad idle and killing when the air is turned on. i checked for codes and its not throwing any.
i cleaned the throttle body, didnt help. i pulled the o2 sensors and they are FULL OF CARBON, BAD!! then i pulled the plugs and they are totally carbon fouled!! why would it all of a sudden start running so rich. and not throwing any codes.
i bought new o2 sensors and new plugs for it, just hate to have it foul those out too.

 

Possibilities that come to mind...

Failing injector(s)
Bad fuel pressure regulator
Weak coil

It won't throw any codes unless it's outside the range of the PCMs ability to make adjustments. Sounds like it needs to be hooked up to a Tech 2 or Autotap in order to see what the PCM is seeing.

 

could have been a series of things...

the plugs get old, and can't fire as well... that leads to a rich condition... the O2 sensors get fouled....

I agree with 007, check the fuel pressure.

 

i put the plugs in and 2 o2 sensors in and no change.
the fuel pressure is the same as its always been, 38-40 psi i have a gauge on the a pillar so i can watch it. when i shut it off the fuel pressure stays at 38-39 psi and doesnt drop any. my a/f meter always stays around .85-.98 but now its staying around .38-.55 so its definitly rich
i can hook my scanner to it and see a live datastream while its running but i dont know what the #s should be so thats useless
and i dont have the stock coil anymore. i'm using the delteq ignition now with the 4 coils.

 

Disconnect the battery or pull the PCM fuse and see if there's any change.

Could also be the IAC motor. Is it only an an idle problem or does it run poorly across the rpm range?

What scan software do you have?

 

it revs clean in nuetral but when driving it surges kinda. like its flooding out. when its idleing you can see the exaust. its puffing black smoke out both sides. and the idle is erradic it goes up and down then kills. i checked all vac lines and couldnt find a leak. i have a mac tools scanner that i can check, erase codes and watch or record live data from the sensors.
this is bad timing with the gathering just days away. now i dont know if i'll be able to make it

 

I thought a 96 has 4 o2 sensors. I do believe my 95 has 4 but I'm not 100% certain. This sounds like my 95 when the left front O2 sensor went bad and no codes. Black smoke, rough idle, and surge when driving...this is what mine did.

 

i recorded some data and here are the results.
02S11 ] .780 [.160 [.185 [.415 [.320 [.750 [.405 [.765 [.700 [.060
O2S12] .705 [.585 [.360 [.610 [.330 [.320 [.305 [.730 [.695 [.595
02S21 ] .055 [.035 [.040 [.045 [.055 [.040 [.045 [.055 [.010 [.080
O2S22] .795 [.595 [.625 [.425 [.590 [.685 [.735 [.760 [.395 [.940
TPS% ] 25.5 [26.3 [26.3 [25.5 [26.3 [26.7 [28.6 [28.6 [19.6 [18.4
MAF(lb/m) ] 5.78 [6.37 [6.61 [6.62 [6.56 [6.98 [6.92 [6.55 [2.02 [12.85
CALC LOAD%] 16.1 [19.2 [19.6 [19.2 [18.4 [19.6 [19.2 [19.2 [5.5 [6.7
RPM ] 2982 [3255 [3270 [3223 [3262 [3223 [3310 [3277 [1370 [2849
MAP(hg) ]10.6 [10.6 [10.9 [10.6 [10.9 [10.9 [10.3 [10.9 [10.6 [6.2
COOLANT (f) ] 185 185------------------------------185 187 187
IAT(f) ]136 [136 [136 [138 [138 [138 [140 [142 [142 [144
IGN ADV ]-43.0 [-44. [-44. [-44. [-44. [-44 [-44. [-40. [-38. [-41.
LT FTRM1% ]-7.0 [-7.0 [-7.0 [-7.0 [-7.0 [-3.1 [-7.0 [-7.0 -[9.4 [-3.1
ST FTRM1% ]3.1 [-1.6 [-3.1 [-2.3 [-1.6 [.08 [-1.6 [ 0.0 [-18.8 [0.8
LT FTRM2% ]25.0 [25.0 [ 25.0 [25.0 [25.0 [25.0 [25.0 [25.0 [25.0 [25.0
sST FTRM2% ]50.0 [50.0 [50.0 [50.0 [50.0 [50.0 [50.0 [0.0 [28.1 [0.0
ST FTRM11% ] 0.0 [-0.8 [-2.3 [-2.3 [-1.6 [-2.3 [-0.8 [-1.6 [-23.4 [0.0
ST FTRM 21%] 50.0 [50.0 [50.0 [50.0 [50.0 [50.0 [50.0 [2.3 [34.4 [1.6


ok, now what the hell does all that mean and does anyone see any problems

 

I was running really rich (96 LT4) then I got a rear 02 sensor code. Installed a New 02 and problem was solved.

Did you replace ALL 4 02s? This is mike wood's old car?

Does the car run better or worse with the MAF disconnected?

 

From what I can tell looks like this one is way off, there is the culprit. Also a drop on the one by it self.
Does anyone else agree?

 

THANKS FOR THE HELP GUYS yep, this is mike woods old GS.
i put 2 new o2 sensors in the r&l front, no change. so i tried to put the 2 that i took out of the front in the rear and i can only get the right side(pass side) out so i changed that one. the left side i have to drop the exaust system to change it so i didnt touch that one.
i have to get it fixed before tues night because were leaving for bowling green for the c4 gathering. whats the problem you guys see.
i disconected the mass air flow and there wasnt any diff. i didnt drive it just let it idle.
i did just now drive it around the block and its poping bad out the exaust and has no power

 

Looks like an O2 sensor took a dump to me. I would replace the one you didn't get to, not sure which one it is from the numbers.

i did just now drive it around the block and its poping bad out the exaust and has no power

This sounds like a blocked cat, but could also be a O2 sensor.
Fuel pressure looks good so that is covered.

i disconected the mass air flow and there wasnt any diff. i didnt drive it just let it idle.

Did a code show up while you had the MAF disconnected, probably should have.

 

Either the passenger side front o2 sensor is bad or you have a wiring problem with that sensor.

The voltage is waaaaaay low and not fluctuating
The Long Term Fuel on Bank 2 is pegged, dumping all kinds of fuel into the cylinders

 

thanks jim i'm going into the garage right now to pull and have a look at the pass front o2 and wiring
i'll be back

 

i didnt see anything wrong with the wiring but i put the old o2 back in and did a datalog
RPM*****1099**941**1025**979**2407**3579 **3733
O2S11***.915**.230**.690**.150**.895**.9 35**.950
O2S21***.775**.760**.760**.760**.755**.7 55**.755
O2S12***.820**.620**.550**.425**.830**.8 45**.865
O2S22***.245**.200**.200**.205**.925**.9 65**.970
LT FTRM1*10.2**10.2**10.2**10.2**-1.6**-1.6**-1.6
LT FTRM2*22.7**22.7**22.7**22.7**25.0**25.0 **25.0

what ya think, right side still running rich, should i just change all 4 o2 sensors

 

You already changed 2 with new ones. I would either test the one you couldn't get too or it's a bad sensor. Was the one you have to drop the exhaust to get to (one you didn't change) on the right side? If so it needs so be checked or replaced. I can't tell from the scan which on it is.

O2S11***.915**.230**.690**.150**.895**.9 35**.950

O2S22***.245**.200**.200**.205**.925**.9 65**.970

Looks like these are a little high over .9v (low O2 -rich mixture)
Also make sure there are no exhaust leaks in the system giving a false reading.

 

o2s11 is driver frt, o2s12 is driver rr
o2s21is pass frt, o2s22 is pass rr
the one i couldnt get too is the driver rr. and actually the driver side looks ok , the readings fluctuate and the
LT FTRM1*10.2**10.2**10.2**10.2**-1.6**-1.6**-1.6 driver side
looks ok but the pass side still is dumping fuel
LT FTRM2*22.7**22.7**22.7**22.7**25.0**25.0 **25.0 pass side
its the 2 on the pass side that look bad
O2S21***.775**.760**.760**.760**.755**.7 55**.755 front
O2S22***.245**.200**.200**.205**.925**.9 65**.970 rear
the front one is not fluctuating and the rear is lower than the driver side rear. but i'm no pro, i'm just learning all this as i go.
today i will buy 2 new o2 for the pass side and see what happins tonight

 

Just a quick note, more tonight....

The rear o2 sensors have Nothing to do with fuel control on the '96. They are there purely for verification of catalytic convertor operation. All fuel trim control is via the front o2 sensors during closed loop operation.

 

i just put 2 new o2 sensors in the right side and there is no change, still idling high and poping in exaust then it will die.
i'm running out of time and patience
wouldnt a high idle,say @ 1200-1500 mean a vac leak. i checked and couldnt find none. the idle screw is all the way in and not touching the throttle body arm and its still idling high.
what else can i check. i had the battery disconnected all night and day and that didnt help any. back to the garage, i'll run another datalog.

 

this is what i just did, disconected the batt, unpluged the comp and blew out the connections with compressed air,took the maf and duct off and sprayed it with carb cleaner and the iat in the hose behind the maf. took the brand new o2 that i just put in the pass rear out and put it in the driver front so that both l+r fronts have brand new o2s in them. put my original map sensor back in. i had a spare one that i had put in to see if it made a diff.
well after all that i started it up and it was idling high like before,@1400-1600 rpm but not killing. so i took it arond the corner where i can run it. and i hit it from 2nd gear wot till 4th and it wasnt surging or poping. so i turned around and hit it from a dead wot till the top of 4th and no popping or hesitation. it feels like its fixed exept the high idle. it wont come down. when i turn the ac on it comes down to @1000 and its not killing anymore with the ac on.
now i just have to fix the idle. i dont know what i did to fix the running rich and popping and killing condition it had but i'm glad thats fixed.
now, on my datalog at idle it says
abslt tps% 29.4 at 1424rpm and thats at idle. what should the tps % be at idle.
is there a way to adjust the pintle on the iac to bring the idle down