1994 Jimmy rough idle / trouble codes

Scenario: About 10 days ago I took my Jimmy out for a spin. Everything was ok. I stopped and put about 10 gas in; about 20 minutes later the Service
Engine Soon light came on. I stopped at a service station, at which time the thing idled rough as hell. My first thought was water in the gas (from sitting, perhaps from the station I bought gas at [Tessoro]) so I put in a de-icer additive. The condition persisted throughout my 80 mile trip - rough idle, ran ok at higher RPM.
This morning, after learning how to obtain the error codes, I started it up. Same condition, rough idle, smooth at higher RPMs. After letting it warm up (about 15 minutes), the idle smoothed out and the Service Engine light went out. I went ahead to get the error codes: 32 (EGR) and 34 (MAPS). I then started it back up, Service Engine Soon light stayed off, idle remained smooth. I took it for a 5 mi test drive, got home and it remained smooth idle, light out.
Is it possible for water / ice in the fuel / fuel lines to cause this condition and throw these errors? What else would cause these symptoms and error codes, that would just "go away"? I am still thinking water in the fuel.
The vehicle is 94 Jimmy 4.3L V-6 Vortex series W
Thanks for your thoughts/opinions.
steve
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The EGR on these is prone to clogging with carbon. Cleaning/replacing the EGR is a fix for this.
Another possible culprit, though the symptoms come on slowly, is a leaking fuel pressure regulator. I'd suspect EGR before the regulator, which is part of the injector assembly...
On 26 Nov 2003 11:12:58 -0800, snipped-for-privacy@hotmail.com (Steve) wrote:

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Carbon sticking the EGR open, Causes a BIG air leak and low vacuum, Which is why you get the 32 and 34 codes.
Best repair is to pull the EGR and put a http://www.tomco-inc.com/ EGR screened gasket on it. I can Guarantee you IT WILL HAPPEN AGAIN. GM has a revised program for the computer that opens the EGR and cycles it to clear it, but the hunks of carbon still jam it open. The gasket/screen unit keeps the crap out of the valve entirely and prevents it from happening. I made one out of a heli-coil for in my wifes because I got sick of pulling the valve off to clear it out. Although I did get down to under 15 minutes to r&r and knock the carbon out.
--
Steve W.
Life is not like a box of chocolates
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It WILL happen again, huh? nearly 60,000 miles after the EGR clogged the first time, it STILL hasn't clogged again. Clogged at 60,000 the first time. Had a GM dealer replace the valve and put in the updated PROM under terms of a TSB that allowed for free replacement due to being within time and mileage limits.
Steve, you did the CPI unit a while back, didn't you? How's that holding up for you? I did mine over a year ago, only put 14,000 on since I did it, but it's going strong...
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