Hey guys i have a 95 tahoe and it just started running rough lately. In the morning when i first start it, it stumbles and coughs, and hesitates. But when it warms up it has a noticeable misfire and only at idle. If you rev it to 1000 rpm it doesnt misfire or stumble. But if i let it idle it will misfire and the rpm's will change like its surging and it will eventually stall. I've replaced the typical cap, rotor, plugs, and wires but it still has me stumped. Also it runs rich. Could the o2 sensor have gone bad, or could the fuel pressure regulator be causing this? Please any info would be great.
Running rough and rich at idle
- Thread starter 95slowhoe
- Start date
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SunlitComet
OBS Jedi-Do Good
You can pull your own codes to help diagnosis. Drivers side bottom of dash is a connector with 12 terminal slots. With the ignition off short together(paper clip works well the 2 far right terminals on the upper half only. Turn ignition on but do not start. Check engine light will blink once, a short pause, then blink twice indicating code 12. It will repeat 2 times. Each new code will flash 3 times before it moves to the next. There will be a longer pause between different codes. Write back with any codes you have so we can help.
SunlitComet
OBS Jedi-Do Good
Non emmision related codes can show up and not set a light in OBD2 but I am not sure about OBD1 yet. Like I said you don't need a scanner so you can do it yourself and see. Access to codes for yours I have.
well yesterday i was looking at the injectors while it was running. And found one of the two was flooding the throttle body. So i dug through my box of parts and found the original injectors for it. So when i get some time im going to take them to a local diesel shop and they will clean and flow them.
SunlitComet
OBS Jedi-Do Good
DTC 35
http://www.sunlitcomet.com/images/automotive/92-95/42401978.gif
http://www.sunlitcomet.com/images/automotive/92-95/42401977.gif
CIRCUIT DESCRIPTION
The control module controls engine idle speed with the Idle Air Control (IAC) valve. To increase idle speed, the control module retracts the IAC valve pintle away from its seat, allowing more air to pass by the throttle bore. To decrease idle speed, it extends the IAC valve pintle towards its seat, reducing bypass air flow. A Tech 1 scan tool will read the control module commands to the IAC valve in counts. Higher the counts indicate more air bypass (higher idle). The lower the counts indicate less air is allowed to bypass (lower idle).
DTC 35 WILL SET WHEN
The PCM sees a different reading in desired IAC and actual IAC.
ACTION TAKEN (PCM WILL DEFAULT TO)
None. The PCM turns "ON" the Malfunction Indicator Lamp (MIL) .
DTC 35 WILL CLEAR WHEN
Conditions for fault are no longer present and Tech 1 "clear DTCs" function is used or 50 ignition switch keycycles have passed with no further faults or ignition switch is turned "OFF" and battery feed voltage is removed for 10 seconds.
DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. The IAC tester is used to extend and retract the IAC valve. Valve movement is verified by an engine speed change. If no change in engine speed occurs, the valve can be retested when removed from the throttle body.
2. This step checks the quality of the IAC movement in Step 1. Between 700 rpm and about 1500 rpm, the engine speed should change smoothly with each flash of the tester light in both extend and retract. If the IAC valve is retracted beyond the control range (about 1500 rpm), it may take many flashes in the extend position before engine speed will begin to drop. This is normal on certain engines, fully extending IAC may cause engine stall. This may be normal.
3. Steps 1 and 2 verified proper IAC valve operation while this step checks the IAC circuits. Each lamp on the node light should flash red and green while the IAC valve is cycled. While the sequence of color is not important, if either light is "OFF" or does not flash red and green, check the circuits for faults beginning with poor terminal contacts.
IAC VALVE RESET PROCEDURE
* Disconnect negative battery cable for 10 seconds then reconnect cable battery.
* Key "ON," engine "OFF."
* Ignition "OFF" for 10 seconds.
DIAGNOSTIC AIDS
A slow, unstable, or fast idle may be caused by a non-IAC system problem that cannot be overcome by the IAC valve. Out of control range, IAC Tech 1 scan tool counts will be above 60 if idle is too low, and zero counts if idle is too high. The following checks should be made to repair a non-IAC system problem.
* VACUUM LEAK (High Idle) - If idle is too high, stop the engine. Also, check for binding of throttle blade or linkage.
* SYSTEM TOO RICH (Low Air/Fuel Ratio) - The idle speed will be too low.
* THROTTLE BODY - Remove IAC valve and inspect bore for foreign material.
* IAC VALVE ELECTRICAL CONNECTIONS - IAC valve connections should be carefully checked for proper contact.
* CRANKCASE VENTILATION VALVE - An incorrect or faulty crankcase ventilation valve may result in an incorrect idle speed.
* A/C COMPRESSOR OR RELAY FAILURE - Refer to A/C diagnosis if circuit is shorted to ground.
* If intermittent poor driveability or idle symptoms are resolved by disconnecting the IAC, carefully recheck connections, valve terminal resistance or replace IAC.
* Refer to Diagnosis By Symptom / Stalls / Rough, Unstable Or Incorrect Idle See: Symptom Related Diagnostic Procedures\Rough, Unstable or Incorrect Idle/Stalling
DTC 22
http://www.sunlitcomet.com/images/automotive/92-95/42390820.gif
http://www.sunlitcomet.com/images/automotive/92-95/42390818.gif
CIRCUIT DESCRIPTION
The Throttle Position (TP) sensor provides a voltage signal which changes relative to the throttle blade. Signal voltage will vary from about 0.5 volt at idle to about 4.0 volts at Wide Open Throttle (WOT) .
The TP signal is one of the most important inputs used by the ECM for fuel control and for most of the ECM control outputs.
On non-adjustable TP switches, each time voltage drops below 1.25 volts and stops, the ECM assumes this value is 0 throttle angle and measures percent throttle from this point on.
DTC 22 WILL SET WHEN
* Engine running.
* TP signal voltage is less than 0.2 volt for two seconds.
ACTION TAKEN (ECM WILL DEFAULT TO)
The Malfunction Indicator Lamp (MIL) will illuminate.
DTC 22 WILL CLEAR WHEN
Conditions for fault are no longer present and Tech 1 "Clear DTCs" function is used or 50 ignition switch keycycles have passed with no further faults or ignition switch is turned "OFF" and battery feed voltage is removed for 10 seconds.
DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This step checks to see if DTC 22 is the result of a hard failure or an intermittent condition.
2. Simulates DTC 21: (high voltage) - If the ECM recognizes the high signal voltage, the ECM and wiring are OK.
3. The ECM recognizes the voltage as over 4 volts, indicating that the TP signal circuit and the ECM are OK.
4. This simulates a high signal voltage to check for an open in the TP signal circuit.
5. If the 5 volt reference circuit is shorted to ground, there may also be a stored DTC 34.
DIAGNOSTIC AIDS
A scan tool reads throttle position in volts. Should read about 0.45 to 0.85 volt with throttle closed and ignition "ON" or at idle. Voltage should increase at a steady rate as throttle is moved toward WOT.
An open or short to ground in the 5 volt reference circuit or the TP signal circuit will result in a DTC 22.
Refer to Diagnosis By Symptom / Intermittents See: Symptom Related Diagnostic Procedures\Intermittent Condition
Scan TP signal while depressing accelerator pedal with engine stopped and ignition "ON." Display should vary from below 1.25 volts (1250 mV) when throttle was closed to over 4.5 volts (4500 mV) when throttle is held at WOT position.
http://www.sunlitcomet.com/images/automotive/92-95/42401978.gif
http://www.sunlitcomet.com/images/automotive/92-95/42401977.gif
CIRCUIT DESCRIPTION
The control module controls engine idle speed with the Idle Air Control (IAC) valve. To increase idle speed, the control module retracts the IAC valve pintle away from its seat, allowing more air to pass by the throttle bore. To decrease idle speed, it extends the IAC valve pintle towards its seat, reducing bypass air flow. A Tech 1 scan tool will read the control module commands to the IAC valve in counts. Higher the counts indicate more air bypass (higher idle). The lower the counts indicate less air is allowed to bypass (lower idle).
DTC 35 WILL SET WHEN
The PCM sees a different reading in desired IAC and actual IAC.
ACTION TAKEN (PCM WILL DEFAULT TO)
None. The PCM turns "ON" the Malfunction Indicator Lamp (MIL) .
DTC 35 WILL CLEAR WHEN
Conditions for fault are no longer present and Tech 1 "clear DTCs" function is used or 50 ignition switch keycycles have passed with no further faults or ignition switch is turned "OFF" and battery feed voltage is removed for 10 seconds.
DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. The IAC tester is used to extend and retract the IAC valve. Valve movement is verified by an engine speed change. If no change in engine speed occurs, the valve can be retested when removed from the throttle body.
2. This step checks the quality of the IAC movement in Step 1. Between 700 rpm and about 1500 rpm, the engine speed should change smoothly with each flash of the tester light in both extend and retract. If the IAC valve is retracted beyond the control range (about 1500 rpm), it may take many flashes in the extend position before engine speed will begin to drop. This is normal on certain engines, fully extending IAC may cause engine stall. This may be normal.
3. Steps 1 and 2 verified proper IAC valve operation while this step checks the IAC circuits. Each lamp on the node light should flash red and green while the IAC valve is cycled. While the sequence of color is not important, if either light is "OFF" or does not flash red and green, check the circuits for faults beginning with poor terminal contacts.
IAC VALVE RESET PROCEDURE
* Disconnect negative battery cable for 10 seconds then reconnect cable battery.
* Key "ON," engine "OFF."
* Ignition "OFF" for 10 seconds.
DIAGNOSTIC AIDS
A slow, unstable, or fast idle may be caused by a non-IAC system problem that cannot be overcome by the IAC valve. Out of control range, IAC Tech 1 scan tool counts will be above 60 if idle is too low, and zero counts if idle is too high. The following checks should be made to repair a non-IAC system problem.
* VACUUM LEAK (High Idle) - If idle is too high, stop the engine. Also, check for binding of throttle blade or linkage.
* SYSTEM TOO RICH (Low Air/Fuel Ratio) - The idle speed will be too low.
* THROTTLE BODY - Remove IAC valve and inspect bore for foreign material.
* IAC VALVE ELECTRICAL CONNECTIONS - IAC valve connections should be carefully checked for proper contact.
* CRANKCASE VENTILATION VALVE - An incorrect or faulty crankcase ventilation valve may result in an incorrect idle speed.
* A/C COMPRESSOR OR RELAY FAILURE - Refer to A/C diagnosis if circuit is shorted to ground.
* If intermittent poor driveability or idle symptoms are resolved by disconnecting the IAC, carefully recheck connections, valve terminal resistance or replace IAC.
* Refer to Diagnosis By Symptom / Stalls / Rough, Unstable Or Incorrect Idle See: Symptom Related Diagnostic Procedures\Rough, Unstable or Incorrect Idle/Stalling
DTC 22
http://www.sunlitcomet.com/images/automotive/92-95/42390820.gif
http://www.sunlitcomet.com/images/automotive/92-95/42390818.gif
CIRCUIT DESCRIPTION
The Throttle Position (TP) sensor provides a voltage signal which changes relative to the throttle blade. Signal voltage will vary from about 0.5 volt at idle to about 4.0 volts at Wide Open Throttle (WOT) .
The TP signal is one of the most important inputs used by the ECM for fuel control and for most of the ECM control outputs.
On non-adjustable TP switches, each time voltage drops below 1.25 volts and stops, the ECM assumes this value is 0 throttle angle and measures percent throttle from this point on.
DTC 22 WILL SET WHEN
* Engine running.
* TP signal voltage is less than 0.2 volt for two seconds.
ACTION TAKEN (ECM WILL DEFAULT TO)
The Malfunction Indicator Lamp (MIL) will illuminate.
DTC 22 WILL CLEAR WHEN
Conditions for fault are no longer present and Tech 1 "Clear DTCs" function is used or 50 ignition switch keycycles have passed with no further faults or ignition switch is turned "OFF" and battery feed voltage is removed for 10 seconds.
DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This step checks to see if DTC 22 is the result of a hard failure or an intermittent condition.
2. Simulates DTC 21: (high voltage) - If the ECM recognizes the high signal voltage, the ECM and wiring are OK.
3. The ECM recognizes the voltage as over 4 volts, indicating that the TP signal circuit and the ECM are OK.
4. This simulates a high signal voltage to check for an open in the TP signal circuit.
5. If the 5 volt reference circuit is shorted to ground, there may also be a stored DTC 34.
DIAGNOSTIC AIDS
A scan tool reads throttle position in volts. Should read about 0.45 to 0.85 volt with throttle closed and ignition "ON" or at idle. Voltage should increase at a steady rate as throttle is moved toward WOT.
An open or short to ground in the 5 volt reference circuit or the TP signal circuit will result in a DTC 22.
Refer to Diagnosis By Symptom / Intermittents See: Symptom Related Diagnostic Procedures\Intermittent Condition
Scan TP signal while depressing accelerator pedal with engine stopped and ignition "ON." Display should vary from below 1.25 volts (1250 mV) when throttle was closed to over 4.5 volts (4500 mV) when throttle is held at WOT position.
SunlitComet
OBS Jedi-Do Good
No problem I got the 92-95 tech data now. If you need more data just say.
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