I have a 1994 GMC Sierra 4x4 with the 350 tbi. My check engine light has been coming on now for a week, I scaned it and it ran Code 32(EGR Failure) and code 35 (idle air controller) so I replaced the EGR valve and the EGR selinoid. Then a Replaced the Idle air controller. I made sure and had my battery unplugged to reset the codes. As I was driving there was no check engine light but as soon as i came to a stop and idled for a minute it came on. When i started to drive it went off I scanned it again and pulled the same codes. THe truck doesnt run any different, its a good running truck. I have to smog it and the check engine light wont come off . I dont know whats going on I need a little guidance

 

I know I drive a ford but I do also work on my wifes car and that happens to be a chevy. Here is what I know about your problem from my experience working on my wife's

DTC - 32

indicates that the Exhaust Gas Recirculation (EGR) valve diaphragm is not where the ECM expects it to be. The ECM controls the diaphragm with a Pulse-Width Modulated (PWM) waveform. The EGR has a vacuum bleed solenoid that adjusts the vacuum applied to the EGR valve based on this pulse width. If there is sufficient vacuum at the EGR valve, a switch closes to send a signal back to the ECM. The absence of this signal is the bases for code 32.

The conditions for setting this code are:

no vacuum to EGR (switch open),
Code 33 or 34 (MAF error) is not present,
engine running and LV8 is less than 100,
coolant temperature is > 118 deg F (48 deg C),
the EGR solenoid duty cycle is < 65%,
the above conditions are met for more than 25 seconds

Typical causes for this code include:

1) Faulty EGR valve-to-ECM connection
2) Plugged EGR passages and/or sticking EGR valve
3) Defective EGR valve
4) Defective ECM

DTC Code 35

indicates a problem with the Idle Speed Control (ISC) circuit. It will be set when the closed throttle engine speed is 200 RPM above or below the desired (commanded) idle speed for 50 seconds.

Possible causes include:

1. Vacuum Leak (High Idle) - Also check for binding of throttle blade or linkage.

2. System too lean (High Air/Fuel Ratio) - The idle speed may be too high or too low. Check for low regulated fuel pressure, water in the fuel, or a restricted injector.

3. System too rich (Low Air/Fuel Ratio) - The idle speed will be too low. May exhibit black smoke in exhaust. Check for high fuel pressure, leaking or sticking injector.

4. Foreign material in throttle body.

5. Faulty IAC Valve electrical connections.

6. Faulty PCV valve.

7. Faulty IAC.

8. Faulty ECM.

I hope this helps !

 

The only thing Worf forgot to mention was that the passage that both the egr and idle air control valve use should be checked and cleaned....also check your wiring just to be sure its all good and not chaffed or anything

 

Thanks Chris, its still way to early in the morning