Hey everyone. New member here. I have a 1990 corvette auto that I recently aquired. Having problems with idling after motor warms up. Just changed the fuel injector with ones from Jon at FIC, new plugs and wires, cleaned the plenum and intake, cleaned the IAC valve, replaced the fuel filter, and replaced the EGR valve. After all the cleaning and new injectors were installed I started it and it idled WONDERFULLY for 5 minutes or so . Took it around the block and few times and was very happy until I pulled in the garage again and it was back to the surging idle. Any ideas? Would the new EGR valve possibly be stuck open and causing the engine to choke on its own exhaust? My oil pressure switch seems to be on the fritz as well. Would this be causing my fuel pump to become deactivated and loss of fuel? I can step on the pedal and the engine comes to life as it should so I don't think its a fuel delivery problem. Any input is greatly appreciated! Love this site!

 

Does sound like an EGR problem to me, but that may be the power of suggestion. Check your EGR solenoid. It is the little black plastic piece inline on the EGR vacuum valve. The easiest way I can think for you to do this is to simply pull the vacuum line off of the EGR valve and plug it with your finger. This will disengage the EGR and plug the vacuum leak.

 

Sounds good. I will try that when I get home. Thanks for the quick response!

 

my wager would be the o2 sensor got hit by a hurricane/etc, hook a scanner on and see if it toggles hi/low when engine is warmed...if your o2 sensor is old enuf to start school (college ?) put a new one in regardless.

 

I know you cleaned it( cleaning it isnt always a good idea, especially if you push or move the pintle, as the plastic worm gears inside can/will break), but I would almost 100% say it was the IAC. EGR will make the engine die if it was bad. Push on the EGR and watch it kill the motor.

 

Ok so got home and switched out the O2 sensor. Drove it around for 15-20 minutes and it ran GREAT!! As soon as i pulled it into the driveway the service engine light came on again, but i'm idling just fine now. Jumped pins A and G together and it read these codes:

Module #1
Code # H72

Module#4
Code# H23, H32, H46

Any ideas?

 

Code 13
Oxygen Sensor (02S) circuit open - left side on 2 sensor system

Code 14
Engine Coolant Temperature (ECT) sensor -possible circuit high or shorted sensor

Code 15
Engine Coolant Temperature (ECT) sensor -circuit low or open circuit

Code 16
Direct ignition system (DIS), fault line circuit or Distributor ignition system (low resolution pulse) or Missing 2x reference circuit or OPTI-Spark ignition timing system (low resolution pulse) or System voltage out of range

Code 17
Camshaft Position Sensor (OPS) or spark reference circuit error

Code 18
Crank/Cam error

Code 19
Crankshaft Position Sensor (CPS) circuit

Code 21
Throttle Position (TP) sensor circuit - signal voltage out of range, probably high

Code 22
Throttle Position (TP) sensor circuit - signal voltage low

Code 23
Intake Air Temperature (IAT or MAT) sensor circuit temperature out of range, low or Open or grounded M/C solenoid Feedback Carburetor system

Code 24
Vehicle Speed Sensor (VSS) circuit

Code 25
Intake Air Temperature (IAT or MAT) sensor circuit temperature out of range, high

Code 26
Quad-Driver Module #1 circuit or Transaxle gear switch circuit

Code 27
Quad-Driver Module circuit or Transaxle gear switch, probably 2nd gear switch circuit

Code 28
Quad-Driver Module (QDM) #2 circuit or Transaxle gear switch, probably 3rd gear switch circuit

Code 29
Transaxle gear switch, probably 4th gear switch circuit

Code 31
Camshaft sensor circuit fault or Park/Neutral Position (PNP) switch circuit or Wastegate circuit signal

Code 32
Exhaust Gas Recirculation (EGR) circuit fault or Barometric Pressure Sensor circuit low Feedback Carburetor system

Code 33
Manifold Absolute Pressure (MAP) sensor - signal voltage out of range, high or Mass Air Flow (MAE) sensor - signal voltage out of range, probably high

Code 34
- Manifold Absolute Pressure (MAP) sensor - circuit out of range voltage, low or Mass Air Flow (MAF) sensor circuit (gm/sec low)

Code 35
- Idle Air Control (IAC) or idle speed error or Idle Speed Control (ISO) circuit throttle switch shorted Feedback Carburetor system

Code 36
Ignition system circuit error or Transaxle shift problem - 4T60E Transaxle

Code 37
Brake input circuit fault - Torque converter clutch signal

Code 38
Brake input circuit fault - Torque converter clutch signal

Code 39
Clutch input circuit fault - Torque converter clutch signal

Code 41
Cam sensor or cylinder select circuit fault ignition control (IC) reference pulse system fault or Electronic Spark Timing (EST) circuit open or shorted

Code 42
Electronic Spark Timing (EST) circuit grounded or Ignition Control (IC) circuit grounded or faulty bypass line

Code 43
Knock Sensor (KS) or Electronic Spark Control (ESC) circuit fault

Code 44
Oxygen Sensor (02S), left side on 2 sensor system lean exhaust indicated

Code 45
Oxygen Sensor (02S), left side on 2 sensor system rich exhaust indicated

Code 46
Personal Automotive Security System (PASSKey II) circuit or Power Steering Pressure Switch (PSPS) circuit

Code 47
PCM-BCM data circuit

Code 48
Misfire diagnosis

Code 51
Calibration error, faulty MEM-CAL, ECM or EEPROM failure

Code 52
Engine oil temperature sensor circuit, low temperature indicated or Fuel Calpac missing or Over voltage condition or EGR Circuit fault

Code 53
Battery voltage error or EGR problem or Personal Automotive Security System (PASS-Key) circuit

Code 54
EGR #2 problem or Fuel pump circuit (low voltage) or Shorted mixture control solenoid circuit Feedback Carburetor system

Code 55
A/D Converter error, PCM error or not grounded, EGR #3 problem, Fuel lean monitor, Grounded voltage reference, faulty oxygen sensor or fuel lean Feedback Carburetor system

Code 56
Quad-Driver Module (QDM) #2 circuit or Secondary air inlet valve actuator vacuum sensor circuit signal high 5.7L (VIN ***

Code 57
Boost control problem

Code 58
Vehicle Anti-theft System fuel enable circuit

Code 61
A/C system performance or Cruise vent solenoid circuit fault or Oxygen Sensor (02S) degraded signal or Secondary port throttle valve system fault 5.7L (VIN J) or Transaxle gear switch signal

Code 62
Cruise vacuum solenoid circuit fault or Engine oil temperature sensor, high temperature indicated or Transaxle gear switch signal circuit fault

Code 63
Oxygen Sensor (02S), right side circuit open or Cruise system problem (speed error) or Manifold Absolute Pressure (MAP) sensor circuit out of range

Code 64
Oxygen Sensor (02S), right side - lean exhaust indicated

Code 65
Oxygen Sensor (02S), right side - rich exhaust indicated or Cruise servo position circuit or Fuel injector circuit low current

Code 66
A/C pressure sensor circuit fault, probably low pressure or Engine power switch, voltage high or low or PCM fault 5.7L (VIN ***

Code 67
A/C pressure sensor circuit, sensor or A/C clutch circuit failure or Cruise switch circuit fault

Code 68
A/C compressor relay (shorted circuit) or Cruise system fault

Code 69
A/C clutch circuit or head pressure high

Code 70
A/C refrigerant pressure sensor circuit (high pressure)

Code 71
A/C evaporator temperature sensor circuit (low temperature)

Code 72
Gear selector switch circuit

Code 73
A/C evaporator temperature sensor circuit (high temperature)

Code 75
Digital EGR #1 solenoid error

Code 76
Digital EGR #2 solenoid error

Code 77
Digital EGR #3 solenoid error

Code 79
Vehicle Speed Sensor (VSS) circuit signal high

Code 80
Vehicle Speed Sensor (VSS) circuit signal low

Code 81
Brake input circuit fault - Torque converter clutch signal

Code 82
Ignition Control (IC) 3X signal error

Code 85
PROM error

Code 86
Analog/Digital ECM error

Code 87
EEPROM error

Code 99
Power management

 

I had the same thing, but with no codes. Mine only acted up on cold starts and it was the coolant temp switch.
Good luck!

 

thanks Charleston2012 and Jaws89. So the real troubleshooting begins! hahaha, i will keep you guys updated on what I find but the real biggy for the idle surge problem seemed to be the O2 sensor.