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Discussion Starter · #1 ·
As the title states, I've got a 2000 Astro with a rough idle. I rebuilt the engine about a year and a half ago due to a a bent valve, it was torn down to the block sent to the machine shop then rebuilt by me. I've got maybe 25,000 miles with no check engine lights or issues aside from poor gas mileage, about 10mpg. Well recently the check engine light came on as I noticed it was running a bit rough. It was for the upstream o2 sensor, I replaced it and the light stayed on. After doing some research I re-replaced all the o2 sensors with "Delphis" because apparently that's what these 4.3's like, and it did like it, the check engine light turned itself off (such a satisfying feeling) but the rough idle and poor mpgs remained.

The rough idle: The engine will start up without hesitation and run like a damn clock until its up to operating temp. Once at operating temp it idles real rough, not like a misfire (I know the misfire feels all too well, hence the rebuild) but kinda like an engine that's a touch out of time.

Today the check engine light came back on for my new Delphi o2's 馃檭.... This got me thinking (which I should have done a long time ago) I kept assuming my poor mpgs were a result of my engine not being timed with a fancy computer (although now that I think about it I did take it to a shop with a special computer to have it timed correctly) but now I'm fairly certain its because its running way too rich. After searching forums for the possible culprit I read about the coolant temp sensor and how it tells the ECU if the engine is cold or hot resulting in a rich mixture for cold engines and normal mixture for warm engines. I also read that 03-06 Astros or 4.3's with an "X" VIN only have the one sensor between the exhaust manifold rather than both the exhaust manifold sensor and the coolant temp sensor on the intake manifold. I looked back at a photo of my intake manifold during my rebuild and don't see a coolant temp sensor. My VIN has a "W" in it do I not have one?
Other areas I plan on looking at for rich behavior are:
Bad EGR, clogged or dirty?
Fuel pressure regulator, leaky? (New fuel pump and spider assembly upon engine rebuild)
I should check and clean my MAF because its so damn easy but I doubt its that (never that easy of a fix)
What else could cause a rich mixture without throwing a code?
Lastly, can a rich mixture even blow out the o2's like I'm assuming?

It would be rad to actually enjoy all the time and effort I've spent on this van 馃馃馃
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Discussion Starter · #4 ·
It鈥檚 odd because when I scanned the computer it showed these are 鈥渃onfirmed trouble codes鈥 yet the check engine light was NOT on, after it came on it showed the same codes.

P0155- O2 sensor heater circuit bank 2 sensor 1

P0305- cylinder 5 misfire detected

P1351- EST Output high or pulses detected when grounded- cylinder 1

I think p1351 may be attributed to a kill switch I have wired to my fuel pump, which I occasionally forget to flip on before starting.

Regardless, it鈥檚 strange I only have rough idle/ potential rich mixture symptoms AFTER the engine is to operating temp. I鈥檒l have some time to tinker this weekend, maybe I can narrow the prognosis.
 

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Some codes will require multiple instances before they will illuminate the CEL.
P0155 could be a power supply/ground/connector or sensor issue.
P0305, I would fix the other stuff first before worrying about this one.
P1351 is probably a bad ICM or it could be connector/wiring issue as well.

That is because the computer is in open loop, ignoring the o2 sensors until it's warmed up, which once warm it goes into closed loop and starts looking at the feedback from the o2 sensors to keep an optimal air-fuel ratio.
 

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Discussion Starter · #6 ·
This weekend I was able to clean the MAF and change the air filter. I cleared the codes to see what would come back, so far just the misfire has returned along with the rough idle
 

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Discussion Starter · #7 ·
Last weekend I was able to swap the ICM and dizzy cap (which had some oxidation). I had the parts laying around so I thought I may as well. Still have the cylinder 5 misfire code although it really doesn鈥檛 feel or sound like a miss to me, at least not a consistent miss. I may pull the plug this weekend to check, then it鈥檚 going to a proper mechanic鈥.
 
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