rough running now not idling - S-10 Forum
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post #1 of 10 Old 03-16-2017, 09:57 PM Thread Starter
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rough running now not idling

I just recently got this 1993 S10 with the 4.3V6. The seller described the engine as bogging down sometimes, and I experienced that the day I bought it, but I also drove it 45 mins home with minimal "bogging" down. It seems to be temperamental in that I driven it a couple times with no real issues, but the last couple days it will not idle, it has been a good bit colder than normal lately so I am wondering if that is just exacerbating the issue.. The truck starts with no problems, but sounds rough, and will not idle. I am trying to describe the running issues as best I can.. Sometimes pressing the gas while trying to keep it going has no effect on the engine.. I have read that it could be fuel pump related, when the truck does die I can hear the pump "whine" for a couple seconds each time.. I have take a video to try to help describe, but as you will notice in the video the muffler is split so it's loud in general.. I really haven't done a lot of troubleshooting yet as at first the issues were not real prevalent, and more of an after thought that I wanted to get to.. Now that it won't idle I am more concerned about getting it going. Here is the video link if you want to take a listen/watch..



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post #2 of 10 Old 03-16-2017, 10:44 PM
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Re: rough running now not idling

hmm, does this have an idle air control valve? they get carboned up bad on 4.3L and stick.

EGR valves and get stuck to. a 93 probably has a vacuum operated one so feel under the rgr and physically move the diaphram up and down a few times then pop the line off and plug with a golf tee then try starting/driving it.
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post #3 of 10 Old 03-16-2017, 10:56 PM
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Re: rough running now not idling

damn edit timer:

usually fuel pumps when they start to go do several things: long crank times or crank but no start, idles ok drives aroudn town Ok but falls on its face WOT on highway as thats when it needs the most fuel but cant provide it due to low pressure.

if it is a low fuel issue, start it get it stumbling like your video then spray carb cleaner (NOT BRAKE CLEANER) down the intake - if it stalls your not gettign enough air or too much fuel, if it becomes normal then probably not enough fuel or too much air.

id remove, clean and inspect the idle air control valve. dont physically try to move it or you will strip it. Its just a tiny servo motor that moves the rubber valve metering the incomming air - thus if its stickign it cant adjust itself. and clean the valve seat as im sure its carboned up and may not be sealing all the way letting too much air past.
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post #4 of 10 Old 03-16-2017, 11:34 PM Thread Starter
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Re: rough running now not idling

i will say that i did unplug the vac line for the EGR and capped it for a test and while it never had the not idling problem, it did stumble or bogg down so I assumed EGR wasn't the culprit. I will try spraying carb cleaner in the intake, and attempt to locate and clean the IACV.

Thanks

John 14:6
Jesus saith unto him, I am the way, the truth, and the life: no man cometh unto the Father, but by me.

Vehicles
2007 Pontiac G6 (Daily)
1986 Nissan 300zx Turbo
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post #5 of 10 Old 03-17-2017, 07:06 AM
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Re: rough running now not idling

Check all the vacuum lines also to make sure you don't have any leaks. Did you do a complete tune-up when you got it? That's the first thing I would do - cap & rotor, plugs, fuel filter, etc.

94 S10 extended cab, long bed, 4.3L, auto
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post #6 of 10 Old 03-17-2017, 02:07 PM Thread Starter
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Re: rough running now not idling

Quote:
Originally Posted by kevinp1335 View Post
Check all the vacuum lines also to make sure you don't have any leaks. Did you do a complete tune-up when you got it? That's the first thing I would do - cap & rotor, plugs, fuel filter, etc.
I have checked vacuum lines and replaced a couple, I haven't done a complete tune-up.. I am not sure how much time the PO put into fixing the issue.. I hate to redo stuff that has been recently done, I may pull the plugs and see how they look. I do plan to replace the fuel filter Saturday.

I also noticed last night the first time i try to start it, it will start and die pretty much instantly. After that it will "idle" like in the video and die pretty quickly if I don't press the gas..

John 14:6
Jesus saith unto him, I am the way, the truth, and the life: no man cometh unto the Father, but by me.

Vehicles
2007 Pontiac G6 (Daily)
1986 Nissan 300zx Turbo
1993 Chevy S10 Ext. Cab
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post #7 of 10 Old 03-17-2017, 08:29 PM Thread Starter
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Re: rough running now not idling

I jumped the obd connector and got one code.

34 - MAP sensor signal voltage low - MAP sensor signal voltage was too low (high vacuum) when engine speed was over 1200 RPM, or the throttle angle was above 21% when engine speed was over 1200 RPM.

It seems very temperamental.. i went out to get codes and it idled good (well idle fluctuated but sounded "normal") turned if off set the jumper on the OBD connector got codes, cranked it back up and wouldn't idle and ran like trash while holding the pedal down to keep it from shutting down..

I pulled and cleaned the IAC, it was pretty black. I noticed once when i had the air filter and cover off and it shutdown kinda hard a puff of bluish smoke puffed from the TB...

Any suggestions?

John 14:6
Jesus saith unto him, I am the way, the truth, and the life: no man cometh unto the Father, but by me.

Vehicles
2007 Pontiac G6 (Daily)
1986 Nissan 300zx Turbo
1993 Chevy S10 Ext. Cab
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post #8 of 10 Old 03-18-2017, 10:48 PM
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Re: rough running now not idling

CODE 34, MAP SENSOR SIGNAL VOLTAGE LOW
Manifold Absolute Pressure (MAP) sensor responds to changes in manifold pressure (vacuum). If MAP sensor fails, ECM will substitute a fixed MAP value and use TPS input to control fuel delivery.
NOTE:
Test numbers refer to test numbers on diagnostic chart.
1. This confirms Code 34 and determines if code was a hard failure or an intermittent condition. Code 34 will set when ignition is on and MAP signal voltage is low. On some systems, engine must be running to set code.
2. Jumpering harness 5-volt reference circuit and MAP signal circuit terminals will determine if problem is sensor, ECM or wiring. If ECM recognizes and indicates high MAP signal, ECM and wiring are okay.
3. Scan tester may not display 12 volts. The important thing is that the ECM recognizes voltage as greater than 4 volts (high MAP voltage signal), indicating ECM and MAP signal circuit are not at fault.
Diagnostic Aids
With ignition switch in ON position and engine off, manifold pressure is equal to atmospheric pressure and signal voltage will be high. Comparing BARO readings with a known good vehicle using the same sensor is a good way to check accuracy of suspected sensor. Readings should be within .4 volt of each other. A Code 34 will also result if 5-volt reference and MAP signal circuits are open or shorted to ground. If 5-volt reference circuit is not shorted to ground and a Code 22 is stored, check MAP signal circuit for short to ground.
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94 S10 extended cab, long bed, 4.3L, auto
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post #9 of 10 Old 03-22-2017, 03:26 PM Thread Starter
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Re: rough running now not idling

So after much troubleshooting (I will save the long story...) I was able to track down my issue.. I noticed I wasn't getting fuel from the passenger side injector.. When I got the truck PO had the ECM all ghetto zip tied hanging below the glove box. So in my process of moving it back to where it is supposed to go the blue wire from injector to ECM came loose.. Now idling and running great and after a couple days of driving no codes are showing!!

John 14:6
Jesus saith unto him, I am the way, the truth, and the life: no man cometh unto the Father, but by me.

Vehicles
2007 Pontiac G6 (Daily)
1986 Nissan 300zx Turbo
1993 Chevy S10 Ext. Cab
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post #10 of 10 Old 03-22-2017, 08:27 PM
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Re: rough running now not idling

Good deal.

94 S10 extended cab, long bed, 4.3L, auto
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