Hesitation upon take off, engine has a rough idle

Tiny
EARLBELL
  • MEMBER
  • 1997 CHEVROLET SILVERADO
  • 5.1L
  • V8
  • 4WD
  • AUTOMATIC
  • 182,000 MILES
Parked truck Saturday (all was well), went to drive it yesterday and it was idling a bit rough. Took off down the road and it felt hesitant and like it was missing. She was a bit low on oil and I topped her off. Seems okay when she gets up to fifty plus mph. Odd noise coming from around catalytic converter. Weather has been odd here in Georgia.
Tuesday, January 9th, 2018 AT 10:27 AM

26 Replies

Tiny
HARRY P
  • MECHANIC
  • 2,292 POSTS
Take your distributor cap off and check for moisture. If I were a betting man, I would bet that with all the crazy rain/sleet/snow that has happened of late, you got some moisture in there and it is taking out your sparks. Dry it out, replace the cap and rotor, and see how it does.

Also look at this guide

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

Please run down this guide and report back.
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Tuesday, January 9th, 2018 AT 10:34 AM
Tiny
STEVE W.
  • MECHANIC
  • 14,556 POSTS
Also, look at the wires as well if they are older. They can look good but still leak spark when they get a bit damp. Easy way to check that is to wait until it is dark and open the hood, start the engine and look for sparks, to make it easier you can use a spray bottle and mist some plain tap water and watch for them. (Do not use distilled or super filtered water, they will not work because it is the minerals in the water those processes remove that make it conductive)
If you see spark discharging replace the wires and probably the plugs if they have not been done in a while.
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Tuesday, January 9th, 2018 AT 1:12 PM
Tiny
SCOOOOBYT
  • MEMBER
  • 1 POST
  • CHEVROLET SILVERADO
I have a 97 chevy C/K 1500 4x4 and it has a auto trans. It has a 5.7L vortec. Ok my question is my truck ran hot an I had a water leak an I fixed it. Now it idles rough. I though that it had a blown headgasket but it doesn't. But I can not figure out why it is running rough. Could it have a burn't valve. I am having a lot of trouble and I don't want to spend a lot of money if I don't have to.
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Monday, November 16th, 2020 AT 11:34 AM (Merged)
Tiny
MIKE H R
  • MECHANIC
  • 3,094 POSTS
Do a compression check, if any of the readings are more than twenty pounds lower could mean there is a problem with that cylinder or the valves.

https://www.2carpros.com/articles/how-to-test-engine-compression

let us know
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Monday, November 16th, 2020 AT 11:34 AM (Merged)
Tiny
MIKELOWERY44
  • MEMBER
  • 4 POSTS
  • 1995 CHEVROLET SILVERADO
  • 299,000 MILES
Idles rough sometimes dies while idling mainly when the truck is warmed up have already cleared codes and cleaned up ECM ground thinking it may be a cam sensor fault but not sure it also takes a couple seconds to crank after turning the key and the motor has about 80000 miles on it
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Monday, November 16th, 2020 AT 11:34 AM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Try cleaning out the EGR valve and PCV valve and see what happens
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Monday, November 16th, 2020 AT 11:34 AM (Merged)
Tiny
MIKELOWERY44
  • MEMBER
  • 4 POSTS
I've done both just put a throttle position sensor on too and a new throttle body a couple weeks ago and it does have code 41 showing up which is an ignition system error
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Monday, November 16th, 2020 AT 11:34 AM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,125 POSTS
Since the problem is dealing with idle, have you checked for vacuum leaks and checked the idle air control valve (IAC)? The IAC is responsible for the engine's idle.
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Monday, November 16th, 2020 AT 11:34 AM (Merged)
Tiny
MIKELOWERY44
  • MEMBER
  • 4 POSTS
Yup the iac is brand new and the connector is too and I've also replaced a few vacuum lines they all look good
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Monday, November 16th, 2020 AT 11:34 AM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,125 POSTS
Have you checked vacuum at the intake?
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Monday, November 16th, 2020 AT 11:34 AM (Merged)
Tiny
MIKELOWERY44
  • MEMBER
  • 4 POSTS
Sure haven't ill do that and let ya know how it works appreciate it man
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Monday, November 16th, 2020 AT 11:34 AM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,125 POSTS
I'm glad to help. Between me and Rasmataz we will get you going.
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Monday, November 16th, 2020 AT 11:34 AM (Merged)
Tiny
ALKALINE
  • MEMBER
  • 9 POSTS
  • 1994 CHEVROLET SILVERADO
  • 230,000 MILES
When I start the engine it idles fine to begin with. I put it in gear and start driving, and by the time I get to the end of the street it has been stalling. I start it again, and it idles low and rough. When I give it the gas it hesitates badly.

I have replaced the IACV, TPS, ignition coil, cap, and rotor. A couple of months ago I rebuilt the TBI (including new fuel pressure regulator). I removed the EGR valve to examine for carbon buildup in the manifold passages beneath it and they were clear. The EGR valve itself has been replaced within the past few years. The coolant temp sensor on top of the manifold next to the water inlet is also fairly new at around six months old.
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Monday, November 16th, 2020 AT 11:34 AM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,125 POSTS
Is fuel pressure within spec? Have you checked for vacuum leaks? Any trouble codes?
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Monday, November 16th, 2020 AT 11:34 AM (Merged)
Tiny
ALKALINE
  • MEMBER
  • 9 POSTS
The CEL came on twice during the past dozen or so times that I've driven it. On both occasions, the light reset/turned off after I turned the truck off. It is my understanding that I can't retrieve the code if the CEL has gone out. Is that correct?

I have visually inspected all the vacuum lines and can find no leaks.

Fuel pressure is something I've never checked. How can I do this?
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Monday, November 16th, 2020 AT 11:34 AM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,125 POSTS
If it is a hard code, it will stay in memory. If you can, give it a try to see if anything is showing. Also, if this happens when driving, you can use a live scanner to monitor the systems to see what is happening.
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Monday, November 16th, 2020 AT 11:34 AM (Merged)
Tiny
ALKALINE
  • MEMBER
  • 9 POSTS
OK, just checked the code. It gave me a 44.
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Monday, November 16th, 2020 AT 11:34 AM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,125 POSTS
That is for a lean exhaust. Most likely a vacuum leak. Also, it could deal with the temp sensor or low fuel pressure.
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Monday, November 16th, 2020 AT 11:34 AM (Merged)
Tiny
ALKALINE
  • MEMBER
  • 9 POSTS
Just checked for vacuum leaks using some spray carb cleaner. Didn't find any leaks. I also just now replaced the fuel filter.

It is still running rough and almost died when I got to the end of the street like it has been, but it might be running just a tad bit better than it was. I can't really know for sure until later on today/tonight when the temperature outside drops. Cold temperatures exacerbate the problem.

Since it is worse when it is cold outside, does that favor the problem being a bad temperature sensor vs. A bad fuel pump?
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Monday, November 16th, 2020 AT 11:34 AM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,125 POSTS
It could be either. Pumps can act funny in cold weather too.
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Monday, November 16th, 2020 AT 11:35 AM (Merged)

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