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3800 engine runs rough at cold start up

Tiny
FIREMNTED
  • MEMBER
  • 1996 BUICK REGAL
  • 175,600 MILES
15 Miles on rebuilt engine New Temp sensor replaced twice new MAP sensor new TPS New upstream O2S New Thermostat
Saturday, May 5th, 2012 AT 9:57 PM

31 Replies

Tiny
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It sounds like you've already taken several steps to address the rough running issue on your 1996 Buick Regal with a rebuilt 3800 engine. Since you've replaced several sensors and components related to engine performance, there could be a few more possibilities to consider:

Vacuum Leaks: Even if you've replaced the sensors, there could still be vacuum leaks in the intake manifold or other areas of the engine. Vacuum leaks can cause rough idling, especially when the engine is cold.

Idle Air Control (IAC) Valve: The IAC valve controls the engine's idle speed. If it's malfunctioning or dirty, it can lead to rough idling during cold starts. Cleaning or replacing the IAC valve might help.

Fuel Injectors: Dirty or clogged fuel injectors can disrupt the fuel-air mixture, causing rough running. Consider having the fuel injectors professionally cleaned or replaced if necessary.

EGR Valve: A malfunctioning Exhaust Gas Recirculation (EGR) valve can cause rough idling. Make sure the EGR valve is functioning properly and not sticking open or closed.

Air Intake and Throttle Body: Check the air intake system and throttle body for dirt, carbon buildup, or obstructions. A dirty throttle body can affect airflow and lead to rough idling.
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Saturday, May 5th, 2012 AT 10:00 PM
Tiny
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Used injectors but cleaned. Plugs and wires are new and rechecked. The car did sit for 11 months with a full tank of fuel treated with sea foam. I have a scan tool and had no output from the sensors I replaced. The car starts and runs perfectly every time when it gets to 150 deg. F vida the scan tool!
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Saturday, May 5th, 2012 AT 10:08 PM
Tiny
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Monitor the coolant sensor when cold

Roy
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Saturday, May 5th, 2012 AT 10:13 PM
Tiny
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70 Deg. This morning and out side temp. Was 57.2 so I replaced it today with no change
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Saturday, May 5th, 2012 AT 10:16 PM
Tiny
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Air intake temp. Was 47 Deg.
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Saturday, May 5th, 2012 AT 10:18 PM
Tiny
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Air intake will not effect it. It is the coolant sensor, the temp of the coolant. It gives a richer mixture when cold. It may be running lean

Roy
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Saturday, May 5th, 2012 AT 10:20 PM
Tiny
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That was what I thought and why I replaced it a second time day the first was when I rebuilt the engine! I still have the original should I try that?
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Saturday, May 5th, 2012 AT 10:24 PM
Tiny
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The temp sensor you said, was that the sensor by the thermostat housing or on the back of the head

Roy
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Saturday, May 5th, 2012 AT 10:48 PM
Tiny
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Thermostat Housing
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Saturday, May 5th, 2012 AT 11:03 PM
Tiny
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What was the reading on the scan tool when cold?

Roy
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Saturday, May 5th, 2012 AT 11:06 PM
Tiny
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70
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Saturday, May 5th, 2012 AT 11:12 PM
Tiny
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If that is degrees, that sounds right.

What about the mass air flow?

Roy
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Saturday, May 5th, 2012 AT 11:14 PM
Tiny
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I'm not getting a code!
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Saturday, May 5th, 2012 AT 11:17 PM
Tiny
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You dont need a code for it to perform poorly. Besides, a code never identifies a bad part just a failed system

Roy
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Saturday, May 5th, 2012 AT 11:20 PM
Tiny
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The temp. Sensor I replaced has 3 wires and the book said in that case it will have two and one of them will have one wire! Does this sound right I'm not finding it! The gage in the car does read high the fan comes on at 230 Degrees and the gage it just under the red almost on it!
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Saturday, May 5th, 2012 AT 11:24 PM
Tiny
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What did your scanner say when the temp was up. Did the reading on the scanner match the gauge?

Roy
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Saturday, May 5th, 2012 AT 11:30 PM
Tiny
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Reading on the scanner was 230 the dealer told me that was normal but the gage had never gotten that high before the rebuild!
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Sunday, May 6th, 2012 AT 12:14 AM
Tiny
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The Mass Air Flow Sensor is putting out 2.687 volts at 112 degrees (engine temp) and 740 RPM and I raised the RPM to 3000 and no change.
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Sunday, May 6th, 2012 AT 12:24 AM
Tiny
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The voltage should have changed in proportion to the engine speed. If it did not, then you may have a failed mass air flow.

Roy
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Sunday, May 6th, 2012 AT 3:59 AM
Tiny
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Ok the Voltage never changed I will have to get a new one thanks!
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Sunday, May 6th, 2012 AT 1:18 PM

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