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Old 03-18-2010, 12:06 AM   #1
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justlrnin is on a distinguished road
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Default More EGR Valve troubleshooting --92 SC2

So after troubleshooting and finding the ICM bad and replacing it with a J/Y part, I am working on the "rough running above idle" problem.
I have checked the EGR solenoid and the Valve for vacuum leaks -- none.
However, I find the Solenoid passing vacuum when the TPS is barely off idle, especially when engine is hot.
Checked O2 sensor, all sooted up, which made sense due to what I thought was a vacuum leak when solenoid was de-energized.
Cleaned and Checked O2 sensor and it started working again, at least some.
Re-installed O2 sensor. Also have cleaned EGR valve seat.

Tonite I checked everything while running engine and find the engine starts to run rough and weak when the EGR Valve opens. More checking finds the vacuum is very light, however, the EGR opens completely, the engine start running rough. Remove vacuum from EGR valve and it closes and engine cleans up and runs great.

Read on forum and find a posting about the possibility of wrong p/n and even possibly a weak spring in EGR valve.

I was thinking the O2 sensor was "telling" the computer to open the EGR valve due to bad readings, and still might be, but I am really beginning to wonder about the EGR valve spring. Previous owner says she replaced it, but it doesnt make sense that the valve would open completely and the computer wouldn't close it or at least try to modulate it.

After all the testing and rough running, I checked codes and all I got was 12. I was expecting something to be set while I was playing with the EGR vacuum. I don't even think it went to "degraded mode" in the computer.

OldNuc, or some of you experts, got any ideas??
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Old 03-18-2010, 02:09 AM   #2
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bbarbulo is on a distinguished road
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Default Re: More EGR Valve troubleshooting --92 SC2

AFAIK, O2 does not tell the PCM that the EGR needs to be opened. the engine is supposed to stall or run really rough at idle with the EGR open. that means the passages are clear. code 12 is just diagnostic mode = ok. rough running above idle, i'd start with map and tps sensors. and coolant temp also. egr wide open my car runs mint off idle but stalls at idle. thats how it should be.
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egr commanding, egr valve, rough running

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