Idles a little rough and shuts off while driving

SINISTA

MEMBER
1999 CHEVROLET TAHOE
5.7L
V8
4WD
180,000 MILES

My SUV got me to work fine one day, but on the way home began to act really crazy. It would barely accelerate and was constantly backfiring but for very short intervals it would run good. I checked for problems using an obd2 and I received three codes. One for the EGR valve one for the crankshaft position sensor and one for the camshaft position sensor. I replaced all three and also replaced all plugs wires, distributor cap, rotor button, and coil. It still didn't run right and acted as if it wasn't getting fuel. I then replaced the fuel pump and fuel filter and blew out all of the lines to free them from debris. Now the SUV will run but it idles a little rough, but when I drive it will just cut off on me at any given time and it takes a out ten minutes for it to start up again. This is very frustrating in midday traffic. I'm no longer getting any obd2 codes and I'm at a loss as to what could be causing this issue. Please if anyone has any ideas on what could be causing this issue I am begging for your help. This is my only means of transportation and I really don't want to lose my job because of transportation issues.

4 Replies

JACOBANDNICKOLAS

MECHANIC
109,716 POSTS

Welcome to 2CarPros.

You description sounds like a bad crankshaft position sensor. I realize you replaced it, but I question if you got a bad one. Take a look through this link:

https://www.2carpros.com/articles/symptoms-of-a-bad-crankshaft-sensor

With that in mind, when the engine fails to start, you should either 1) check for an RPM signal using a live data scanner. Or, 2) check for ignition spark to the plugs.

If you have a live data scanner, that is the quickest and easiest way to do it. If not, here is a link that explains how it is done:

https://www.2carpros.com/articles/how-to-test-an-ignition-system

Here are a few links that may help you when checking for spark:

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

https://www.2carpros.com/articles/how-to-use-a-voltmeter

https://www.2carpros.com/articles/how-to-check-wiring

Let me know if this helps or if you have other questions.

Take care,
Joe

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Tuesday, March 26th, 2019 AT 6:15 PM

SINISTA

MEMBER
3 POSTS

So I have check for spark. I did it the old fashioned way by pulling a plug wire and using a screwdriver. It is firing. After I wrote out my question I decided to check with the obd2 once more after letting it run until it cut off. I received four codes. P0174 system too lean bank 2, P0155 O2 sensor heater circuit malfunction bank 2 sensor 1, P0300 random/multiple cylinder misfire detected, and P0327 knock sensor 1 circuit low input bank 1 or sensor 1.

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Tuesday, March 26th, 2019 AT 7:31 PM

SINISTA

MEMBER
3 POSTS

Also, I noticed when the key is turned there is a humming noise coming from the engine compartment. It sounded like it was possibly coming from somewhere around the intake but I could not pinpoint it.

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Tuesday, March 26th, 2019 AT 7:52 PM

JACOBANDNICKOLAS

MECHANIC
109,716 POSTS

Welcome back.

You know, the knock sensor has me thinking. It helps the PCM fine tune ignition timing. Take a look through this link:

https://www.2carpros.com/articles/how-a-knock-sensor-works

I attached a picture of the knock sensor location.

Next, the noise you were hearing makes me think it could be a vacuum leak. You have a lean code which is most commonly caused by a leak. Here is a link that shows how to check for a vacuum leak. Check that, too.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Let me know what you find.

Joe

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