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My engine has a rough idle can I fix it?

Tiny
SBURGESS
  • MEMBER
  • 2001 CHEVROLET SILVERADO
  • V8
  • 4WD
  • AUTOMATIC
  • 104,000 MILES
About two weeks ago my truck suddenly began idleing low and rough. At times it would die while sitting at stop lights. I thought it might be the fuel filter so I changed it and the problem still persisted. The spark plugs hadn't been changed in 30k miles so I installed new plugs. It doesn't die or act like it is going to die while at lights now but it still idles rough. Through acceleration the engine is very sluggish and rough. To the point it vibrates the entire truck violently. If you press the gas peddle to the floor for fast acceleration it seems to run fine. The OBD connection is not working for some reason so we cannot diagnose the problem using a OBD Diagnostic Scanner.
What is my next step? Plug wires? Rotor cap? Coils? Is there a way to bench test a coil if one may be the culprit?
Any suggestions would be greatly appreciated.
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Friday, September 25th, 2009 AT 1:59 AM

29 Replies

Tiny
QUAGMIRE86
  • MECHANIC
  • 98 POSTS
The problem sounds very reminiscent of what my truck was doing. Turned out to be a MAF sensor. Here is the location so you can replace yours. Check out the diagrams (Below). Please let us know what happens.
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Tuesday, January 7th, 2020 AT 12:42 PM
Tiny
DSPIN
  • MEMBER
  • 1 POST
The #5 fuel injector was bad for me. This guide help me find it.

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

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Tuesday, January 7th, 2020 AT 12:42 PM
Tiny
OBXAUTOMEDIC
  • MECHANIC
  • 3,711 POSTS
Nice work, we are here to help, please use 2CarPros anytime.
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Tuesday, January 7th, 2020 AT 12:42 PM
Tiny
SILVERADOKID
  • MEMBER
  • 1 POST
My silverado was doing the same thing, where it felt as if the engine was getting choked, and died randomly. Finally got to the point where it died on the highway, and wouldn't start back up. Replace the fuel pump, made a huge difference on mine. The job is not that difficult, the best way by far is taking the bed of the truck off, which is only held on by 8 bolts.
Mine still idles rough, but never dies, starts every time, and has more power.
Hope this helps.
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Tuesday, January 7th, 2020 AT 12:42 PM
Tiny
RUDY8459
  • MEMBER
  • 14 POSTS
  • 2001 CHEVROLET SILVERADO
  • 4.8L
  • V8
  • 2WD
  • AUTOMATIC
  • 138,000 MILES
Rough idle whether cold or at operating temperature. P0300 code sel light is on. I have repaired sever vacuum leaks, replace the intake gasket, removed and cleaned fuel injectors. It had a bad fuel pump, so it was replace along with filter. Truck accelerates nicely and has plenty of power, it just idles rough. Bank 1 has random misfire and is lean according to long term trim. Short term trim is normal. The lean factor occurs once it has warmed up slightly to approximately 140 F. Fuel pressure is good but leak down is kind of weird. I have done several leak down tests and some of the tests have held tight with no drop for fifteen to twenty minutes. While other tests have dropped as much as 30 psi in less than five minutes. I got a bald spot by scratching my head on this one.
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Monday, November 16th, 2020 AT 11:05 AM (Merged)
Tiny
WRENCHTECH
  • MECHANIC
  • 20,762 POSTS
Have you checked to see if the EGR valve might not be closing all the way, possibly due to carbon chunks getting caught in the pintle.
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Monday, November 16th, 2020 AT 11:05 AM (Merged)
Tiny
RUDY8459
  • MEMBER
  • 14 POSTS
No I have not but would that cause problems only on bank 1? Bank 2 is good random misfire is only on bank 1. Will try EGR first thing today. What would cause problems only on 1 bank and why the weird leak down tests?
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Monday, November 16th, 2020 AT 11:05 AM (Merged)
Tiny
WRENCHTECH
  • MECHANIC
  • 20,762 POSTS
How would you know it is only happening on Bank 1? P0300 does not specify any certain cylinders.
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Monday, November 16th, 2020 AT 11:05 AM (Merged)
Tiny
RUDY8459
  • MEMBER
  • 14 POSTS
I took the truck in to have it diagnosed and was told that bank 1 has random misfire cylinders 1, 3, 5, and 7 but could not find the cause of the misfire. They suggested that I have the engine tore down to see if it is a mechanical problem.
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Monday, November 16th, 2020 AT 11:05 AM (Merged)
Tiny
WRENCHTECH
  • MECHANIC
  • 20,762 POSTS
It could. It depends where the valve is located. A bad vacuum leak in that area could also do that. A stuck open EGR would also be a vacuum leak.
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Monday, November 16th, 2020 AT 11:05 AM (Merged)
Tiny
RUDY8459
  • MEMBER
  • 14 POSTS
Any ideas on the fuel pressure leak down tests being so inconsistent? Did repair leak at egr pipe, was a big one. Did smoke test after repair and found nothing else. Is there somewhere else I should be looking for a vacuum leak other than on the engine.
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Monday, November 16th, 2020 AT 11:05 AM (Merged)
Tiny
WRENCHTECH
  • MECHANIC
  • 20,762 POSTS
The fuel can leak either through an injector into the cylinder, though the regulator into the return line or back through the pump into the tank. If you are sure you have a lean condition, that points away from the first one. Check the vacuum line on the regulator to make sure there is no fuel in the hose. A regulator problem wouldn't be intermittent but the check valve in the pump could be.
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Monday, November 16th, 2020 AT 11:05 AM (Merged)
Tiny
RUDY8459
  • MEMBER
  • 14 POSTS
Okay, no fuel in vacuum hose to fpr. Pinched off return line and did another leak down test first two tests were tight, waited for about twenty minutes the did another and pressure dropped about 12 psi in four minutes. Fuel pump is new about three weeks old. If I do a pressure test of fuel supply line will that work for checking the check valve in the fuel pump? Thanks for helping.
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Monday, November 16th, 2020 AT 11:05 AM (Merged)
Tiny
WRENCHTECH
  • MECHANIC
  • 20,762 POSTS
Instead of pinching off the return, pinch off the feed between your gauge and the pump after it has built pressure.

Make sure you do not pinch any plastic lines. Rubber only.
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Monday, November 16th, 2020 AT 11:05 AM (Merged)
Tiny
DAVTOR
  • MEMBER
  • 2 POSTS
  • 2001 CHEVROLET SILVERADO
  • V8
  • 2WD
  • AUTOMATIC
  • 94,000 MILES
Hello,
I have a 2001 chevy silverado with a 5.3 liter when I go to stop real fast or when I have the truck in reverse and backing up it wants to stall and dose some time the idle drops very low also it surges I have replaced the fuell filter plugs wires pvc valve also throttle position senor it also has traction controll please help
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Monday, November 16th, 2020 AT 11:05 AM (Merged)
Tiny
DAVTOR
  • MEMBER
  • 2 POSTS
I have also taken to the shop as to where they tested the fuel pressure and all sensor and they could not find a problem with my truck or as they put it they know there is a problem but they dont know what it is
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Monday, November 16th, 2020 AT 11:05 AM (Merged)
Tiny
RUDY8459
  • MEMBER
  • 14 POSTS
Hello, sorry about the long delay in answering. Should I get a new MAF? It seems to run better when disconnected.
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Monday, November 16th, 2020 AT 11:05 AM (Merged)
Tiny
WRENCHTECH
  • MECHANIC
  • 20,762 POSTS
Yes I would
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Monday, November 16th, 2020 AT 11:05 AM (Merged)
Tiny
RUDY8459
  • MEMBER
  • 14 POSTS
OK, will check for that rubber section. If I pinch off the feed how will that work on the fuel pump check valve?
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Monday, November 16th, 2020 AT 11:05 AM (Merged)
Tiny
WRENCHTECH
  • MECHANIC
  • 20,762 POSTS
If you build up pressure and then pinch off the line between the gauge and the tank, you are blocking off the check valve.
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Monday, November 16th, 2020 AT 11:05 AM (Merged)

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