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New here, engine running rough

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Old 12-25-2018, 10:43 PM
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Default New here, engine running rough

Hey everyone! I'm new to this forum. I've been a technician for a few years and im stuck on my newly acquired 2002 Blazer 2wd with 131000 miles on it. When I traded it for my old truck I noticed it ran pretty rough. Did a tune up on it. Plugs,wires,cap,rotor, fuel filter. It's running better but still rough at warm idle. At stops in and out of gear it idles ~500rpm and shakes the rig. I've clearned throttlebody and MAF, to no avail. Temperature has been double checked, coil obviously works or else it wouldn't run. It doesn't sound like a vacuum leak. Battery SOC is good-okay. What are some options I have to see if I can make it run a bit better? BTW. I need to add that the old fart who had it before me decided to run 20/50 in it for about 12000 miles.
 
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Old 12-26-2018, 11:44 AM
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how good of shape is the crappy factory plastic distributor and have you checked fuel pressure ?, I'm guessing it doesn't log miss fires in the computer...
 
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Old 12-26-2018, 12:09 PM
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These trucks are known for being very finicky with regard to the use of AC Delco ignition parts, especially the rotor and distributor cap. They are also known for having vacuum leaks due to physical deterioration of the several vacuum lines in the engine compartment. I even saw a post where the problem with poor running was all due to the crank-case ventilation tube being disconnected from the rear-facing side of the throttle-body snorkel.

And ditto on checking the fuel pressure.

I'm sure you don't have to be told to check the easy stuff first!
 
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Old 12-27-2018, 06:20 PM
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Investigated after work today, still can't find anything. Everything's been replaced with Delco parts, it runs okay, I just can feel a tad bit of a misfire and for some reason now it's only in drive now at stoplights, etc. I'm wondering if maybe that transmission is getting worn out?
 
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Old 12-27-2018, 07:13 PM
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Do a test. Put it in neutral or park and let it idle. Then press the brake down firmly and hold it. see if it starts idling rough. If it does I would suspect a vaccumn booster issue.

the boosters tend to go bad and it creates a vaccumn leak while the brakes are activated. one sign is the vehicle running rough when on the brakes. Typically you would only notice this in drive at a stoplight because it's the only time you're holding brake pressure for an extended time.
 
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Old 12-27-2018, 10:06 PM
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Would my instrument cluster be going out? Oil pressure and temp is low, temp is about 150 at Max and oil pressure is about 25-30. Just bought this rig and my experience is German cars and Chrysler. There's a few things about this I can't quite put my finger on, I've got a few issues but the running issue is my main concern because I need to keep this rog reliable
 
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Old 12-28-2018, 07:09 AM
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That is fairly typical oil pressure, although your coolant temp is low. Possibly a thermostat stuck open? I have heard of bad temp. Sensors causing rough running..m but it doesn't fit the bill of only at a stoplight
 
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Old 01-02-2019, 01:14 PM
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Well update from over the holiday. I got a p0420 catalyst low efficiency code about 3 days ago. Monitored a bunch of stuff on it. Im still seeing a misfire every so often on cylinder 1 and cylinder 3. Checked o2 sensor voltages. After the rig is warmed up, the bank 1 sensor 2 are not completely mimicking each other but pretty close. My cat does sound like it rattles, I'm getting a feeling I need a new cat, everything in the ignition is brand new and I know the plugs are gapped correctly. The guy I traded this rig for said he got the fuel pump done by a dealership, but I think a fuel pressure test would be a good idea as well. I'll need to wait a few days to do it but will update as soon as I can. If there's anything else that anyone can think of to test let me know!
 
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