rough when cold. CEL on

[X3N0N]

took off the intake manifold to find the EGR ports were clogged. Cleaned the ports out and reinstalled the throttle body and intake manifold. Checked the timing and it is set at 0 degrees at idle. Idles very rough when cold and will die out if the gas pedal is not pressed. After warming up, the truck runs fine and does not die. Check engine light comes on only at idle, but when its in motion the engine light goes off. Comes back on when stopped. Checked codes and got 12, 33, 35, 42. Any thoughts?

95 2 dr tahoe 5.7L 4x4

[SunlitComet]

Based on codes I would look for a broken ECM ground on the engine some where and verify those sensors are getting the required 5v reference votage that they so much require. The circuits start in the pcm to the sensors and back to the pcm.

DTC 13 - Oxygen Sensor Circuit
DTC 14 - Engine Coolant Temperature (ECT) Sensor Circuit Low(High Temp.)
DTC 15 - Engine Coolant Temperature (ECT) Sensor Circuit High (Low Temp.)
DTC 16 - VSS Buffer Fault
DTC 21 - Throttle Position (TP) Sensor Circuit (High Sig.)
DTC 22 - Throttle Position (TP) Sensor Circuit (Low Sig.)
DTC 24 - Vehicle Speed Sensor (VSS) Circuit Low (Trans Output Speed Signal)
DTC 28 - Transmission Range (TR) Pressure Switch Assembly
DTC 32 - Exhaust Gas Recirculation (EGR) Error
DTC 33 - Manifold Absolute Pressure (MAP) Sensor Circuit High (Low Vacuum)
DTC 34 - Manifold Absolute Pressure (MAP) Sensor Circuit Low (High Vacuum)
DTC 35 - Idle Air Control (IAC) Error
DTC 37 - Brake Switch Stuck "ON"
DTC 38 - Brake Switch Stuck "OFF"
DTC 39 - TCC Stuck "OFF"
DTC 42 - Ignition Control (IC) Error
DTC 43 - Knock Sensor (KS) Circuit
DTC 44 - Lean Exhaust
DTC 45 - Rich Exhaust
DTC 51 - PROM MEM/CAL Error
DTC 52 - System Voltage High Long
DTC 53 - System Voltage High
DTC 54 - Fuel Pump Relay Circuit (Low Voltage)
DTC 55 - Faulty PCM
DTC 58 - Transmission Fluid Temperature (TFT) Sensor Circuit Low (High Temperature Indicated)
DTC 59 - Transmission Fluid Temperature (TFT) Sensor Circuit High (Low Temperature Indicated)
DTC 66 - 3-2 Control Solenoid Circuit Fault
DTC 67 - Torque Converter Clutch (TCC) Solenoid Circuit Fault
DTC 68 - Trans Component Slipping
DTC 72 - Vehicle Speed Sensor (VSS) Circuit Loss (Trans Output Speed Signal)
DTC 73 - Pressure Control Solenoid (PCS) Fault (Current Error)
DTC 74 - Transmission Input Speed (TIS) Sensor Circuit
DTC 75 - System Voltage Low
DTC 79 - Transmission Fluid Over Temp
DTC 81 - 2-3 Shift Solenoid Circuit Fault
DTC 82 - 1-2 Shift Solenoid Circuit Fault
DTC 83 - Torque Converter Clutch (TCC) Pulse Width Modulated (PWM) Solenoid Circuit
DTC 85 - Undefined Ratio Error
DTC 86 - Low Ratio Error
DTC 87 - High Ratio Error

[fyremanpat]

12 is no pulse from distributor

[SunlitComet]

I thought code 12 was when entering diagnostic mode? At any rate I forgot to mention it. Sorry

[X3N0N]

I also thought code 12 showed that you were in diagnostic mode also, from my research... either way i still cant figure out the problem.... just odd that the light turn off when driving.

[retorq]

This may not help but I just got an ALDL cable so I can datalog some stuff incase I need to get a new chip burned. The amt of data is just insane ... any who with one of these you can easily tell if everythign is working and I would imaging tracking down a faulty sensor will be pretty dang easy with this.

[SunlitComet]

X3, were you using a basic code scanner/ key on/off method or do you have access to a real OBD1 scanner?

[fyremanpat]

You guys are right about code 12. My bad. I swear I read it somewhere that there's no pulse from distributor... what about a vacuum leak around the TB? Bolts loose or o ring missing or damaged?

[X3N0N]

key on with the obd connector and a paper clip. ill check for vacuum leaks, but its hard when the truck dies at idle to try and find a leak. I did re use the old tb gasket but covered it in silicone... and the gasket wasnt in real bad shape.

[retorq]

Ditch that sillycone covered gasket and get a good one. You would be able to hear a gasket leak ... get some vacuum plugs while you are getting a new gasket. Unplug everything, cap it and add it in one by one and see.

[X3N0N]

no leaks around the intake gasket or TB gasket. Truck sat for a couple days and i started when i got home from work. Truck started without having to step on the gas pedal and would idle. right after start it would misfire real bad for a few seconds, then the engine light would come on and the truck would idle fine, no misfires. Codes 35 and 42, im gonna try replacing the IAC and the pigtail. Using my power probe shows to have good power and ground to the IAC. Anyone have a wiring diagram for that stuff? just trying to see if i am missing a ground somewhere....

[retorq]

I was getting a 42 (I think it was 42 ..) code after my recent chip upgrade. I unplugged my computer and reseated the chip. That was listed as a possibility ... fixed mine. :|

[SunlitComet]

Exactly what diagrams do you need and I will get them for you.

[X3N0N]

I guess just the electrical components under the hood like the IAC, Throttle body, distributor...etc. ill try reseting the pcm and see if that route works.

[SunlitComet]

http://www.sunlitcomet.com/pdf/automotive/tahoe/92-95/1995-Chevy-Tahoe-4WD-V8-350-4L60E-PCM-Diagram.pdf

http://www.sunlitcomet.com/pdf/automotive/tahoe/92-95/1995-Chevy-Tahoe-IAC-Testing.pdf


grounds:

G100 RH front of engine
G101 RH inner fender, near battery
G101 Sheet metal at RH front wheelhouse
G102 (VIN N) RH front of engine block, near damper pulley
G102 (VIN Z, H, K) LH front of intake manifold
G103 (Gasoline) Top front center of engine (gas)
G103 (VIN H, K) LH front of engine near thermostat housing
G103 (VIN N) LH front of engine near thermostat housing
G103 (VIN Z) LH front of engine near thermostat housing
G104 (VIN H, K) LH front of intake manifold
G104 (VIN N) LH front of engine near thermostat housing
G104 (VIN Z) RH top of cylinder head, near center
G105 (VIN Z H, K) RH front wheelhouse
G106 On intake manifold
G112 RH front of engine compartment, below underhood reel lamp
G113 On radiator support, near LH Headlamp
G150 On thermostat housing
G200 Behind LH side of I/P, below fuse block
G201 Behind LH side of I/P, below fuse block
G202 I/P harness, 15 cm from data link connector
G400 (Suburban) At RH C-pillar
G400 (Utility) At RH C-pillar
G400 RH "B" pillar
G401 Rear of LH framerail, behind bumper
G403 LH trailer hitch support
G404 On # 1 roof bow
G405 On # 1 roof bow

[X3N0N]

thank you, though the first link does not work and is showing me an error page.

[X3N0N]

all fixed, thanks for all the thoughts guys.

[SunlitComet]

Sorry about the link problem but glad it is okay now. What was at fault?

[X3N0N]

I was a dingbat and had the map sensor vacuum hose routed wrong with another vacuum hose. Rerouted and now no more check engine light.

[fyremanpat]

No problem! That's what we are all here for.