Roughs idle

Tiny
E_AMADOR956
  • MEMBER
  • 1999 CHEVROLET TRUCK
  • V8
  • 2WD
  • AUTOMATIC
I have a 1999 chevy that has a rough idle and smokes white. When I rev the engine to about 2000 rpm roughness goes away but still smokes. When it is started for the first time in the morning a black cloud of smoke comes out. All filters have been replaced all 8 injectors have been replaced. Any help would be appreciated.
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Monday, January 3rd, 2011 AT 5:49 PM

33 Replies

Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
Is the MIL indicating and have you tried to retrieve for trouble codes?
Symptom indicates a possible misfiring cylinder.
Was the distributor in anyway adjusted? Have you checked the distributer with crank sync?
Was any repair to engine components made prior to this occurring?
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Monday, January 3rd, 2011 AT 9:26 PM
Tiny
E_AMADOR956
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  • 12 POSTS
No check engine ligh is not on. This vehicle does not have a distributor its a diesel engine not a gas. All filters have been changed
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Monday, January 3rd, 2011 AT 10:17 PM
Tiny
KHLOW2008
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Sorry, it should have been the injection pump timing.
Did you test if any cylinders I snot firing correctly?

Try cracking the injector line cylinder by cylinder to check if any is not functioning correctly.
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Tuesday, January 4th, 2011 AT 1:58 PM
Tiny
E_AMADOR956
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  • 12 POSTS
Already tried that all 8 inj have been replaced and when I remove injectors like you say it make a little difference but engine still rough and smoking but when I accelerate it goes away but smoke still present. Smoke is white
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Tuesday, January 4th, 2011 AT 2:56 PM
Tiny
KHLOW2008
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  • 41,815 POSTS
Performing the above does not necessarily mean to check for faulty injectors. It is to locate any cylinder that is not firing correctly. It could be a fault with compression.

Did all cylinder shows similar amount of difference in engine running condition or did any one or more showed a more significant difference?

Do you have coolant losses issues and did engine ever overheated badly?

White smoke is usually due to non firing conditions or timing is too advanced. It could also mean a minimal amount of water is getting to the cylinders, either due to a bad head gasket or bad cylinder head.
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Tuesday, January 4th, 2011 AT 3:14 PM
Tiny
JTEMPLE42000
  • MEMBER
  • 1 POST
  • 1999 CHEVROLET TRUCK
99 Blazer 130,000miles 4.3L V-6

I have been beating my head against the wall on this one. Over the course of the past few days I have dumped just over $300 dollars into parts and nothing has changed. No Codes other than a P0452 Evap low code(been getting this one for a while, but hasn't created any drivability problems.) The problem started while I was driving. The truck would run fine down the road then when I let off the gas to stop it would die. It always starts right back up. In two days it went from dying a couple times, to dying everytime I stop. I have replaced the IAC, EGR, and the MAP sensor, problem worse now. Used a fuel pressure gauge on the fuel system and pressures are good. Used a scan tool to check other systems, MAF, IAT, TPS, etc, everything looks good. Heres the odd thing though. The new MAP sensor is giving some really strange numbers, same thing the old one did. Haynes book says 1.5-2volts at idle and 4.5 full throttle, I get 1.70v at idle. As I depress the gas pedal, the voltage goes down, not up. The more pedal I give it the more the voltage goes down, never higher than 1.0 volt and as low as.5volt. I'm going to try to swap out the new MAP sensor for another new one and see if I happened to get a bad MAP sensor, but the old one acted the same way. I have no idea what to look at next. PCM? I have replaced all plugs and wires, cap and rotor, and the fuel pump within the last year. Put a new MAF on it about 2 years ago.
Any help would be greatly appreciated.
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Sunday, January 5th, 2020 AT 5:57 PM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Check your vehicle speed sensor
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Sunday, January 5th, 2020 AT 5:57 PM (Merged)
Tiny
SPLIFFY
  • MEMBER
  • 3 POSTS
  • 1998 CHEVROLET TRUCK
  • V8
  • 4WD
  • AUTOMATIC
  • 14,400 MILES
Hello, I have had this truck for 5 years with no problem. A friend borrowed truck to haul equipment 1000 miles away. When he brought it back, he said it will not idle and would barely stay running. (Nice friend). So here I am with a problem. I changed all plugs, wires and rotor. Flushed radiator, changed oil, oil filter, new power steering fluid, new brake fluid, and cleaned air filter. I pulled off intake and sprayed carb cleaner. I added marvel mystery to gas and filled tank up. With all that being done, it still has a rough idle around 400 on RPM gauge. Oil gauge fluctuates around 40. Headlights are dim, but when accelerator is pressed they go bright again. I definitely here a ticking under the hood. Fuel module in gas tank was replaced around 6000 miles ago. I also replaced the fuel filter about a month ago. Please help, I am confused. Could it be IAC, MAF or what?
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Sunday, January 5th, 2020 AT 5:57 PM (Merged)
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
Is the ses like on, when your having the problem? Have the codes checked, some of the national brand autostores will check codes for free if you can get the vehicle down there. If there is a misfire code, it might tell you which cylinder/s is having the problem.

If you think the problem is a fuel issue, start by checking the fuel pressure. I don't care if everything is brand new, I'd still check fuel pressure.

As far as the fuel issue, if you have the csfi fuel system, there are bulletins about cleaning the fuel poppets. That is a shop procedure, I don't think pouring stuff in the tank will help
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Sunday, January 5th, 2020 AT 5:57 PM (Merged)
Tiny
SPLIFFY
  • MEMBER
  • 3 POSTS
This is the CSFI vehicle. The SES light does stay on all the time (3+ years now). I am a girl however I love to work on this thing. So should I go ahead and take the intake off and get started on the poppets? Would this make the truck have a missing sound almost like a tappet sound? The belt definitely needs to be changed.
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Sunday, January 5th, 2020 AT 5:57 PM (Merged)
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
The po300 code can be awkward to track down, I sent you a private message, I don't know if you received it? Goodluck
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+1
Sunday, January 5th, 2020 AT 5:57 PM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
1998 Chevy Truck Rough idle OBD Code P0300-Random Misfire normally results from vacuum leaks or bad fuel

Misfiring can be caused by worn or fouled spark plugs, a weak spark (weak coil, bad spark plug wire), loss of compression, vacuum leaks, anything that causes an unusually lean fuel mixture (lean misfire), an EGR valve that is stuck open, dirty fuel injectors, low fuel pressure, or even bad fuel
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Sunday, January 5th, 2020 AT 5:57 PM (Merged)
Tiny
WEVO5922
  • MEMBER
  • 1 POST
  • 1998 CHEVROLET TRUCK
  • 4.3L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 200,000 MILES
I recently changed motors I have a 1998 chevy ext cab 5 speed well ichanged it to a 700r turbo automatic and put a motor out of a 2002 gmc sierra 1500 well I putit all together now it idles rough when u give it gas it dies I put it on computer and it gave code po118 n po115 help please
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Sunday, January 5th, 2020 AT 5:58 PM (Merged)
Tiny
WRENCHTECH
  • MECHANIC
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You have a problem with the coolant temp sensor circuit. Double check the wiring and make sure none of the pins got bent over or the wires aren't frayed at the connector.
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Sunday, January 5th, 2020 AT 5:58 PM (Merged)
Tiny
GARTHR
  • MEMBER
  • 2 POSTS
  • 1997 CHEVROLET TRUCK
MY 1997 with 133,000 miles chevy pick up has a rough idle. After the vehicle warms up and it starts about 30 seconds after comming to a stop. I put new plugs in and it seemed to help a little but has not solved the problem. Any suggestions would be greatly appreciated.
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Sunday, January 5th, 2020 AT 5:58 PM (Merged)
Tiny
CARUNDELL
  • MECHANIC
  • 602 POSTS
Hey garth,
By chance is the check engine light on or flashing? You may also need to complete your tune up w/ a dist cap/rotor and wire set (if installed) Let me know!

Chris
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Sunday, January 5th, 2020 AT 5:58 PM (Merged)
Tiny
GARTHR
  • MEMBER
  • 2 POSTS
Chris, old plugs looked good. Dist, wires & rotor changed @ 75000. Think maybe Oxygen sensor? Check engine light stays on for days and then goes off for a day or 2.
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Sunday, January 5th, 2020 AT 5:58 PM (Merged)
Tiny
CARUNDELL
  • MECHANIC
  • 602 POSTS
Garth,
I would recommend 1. Finish the tune, cap/rotor/wireset as its close to the recommended time frame. 2. Get the truck scanned for codes and get back to me with the codes and code descriptions. Let me know!

Chris
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Sunday, January 5th, 2020 AT 5:58 PM (Merged)
Tiny
SHUFF2249
  • MEMBER
  • 11 POSTS
  • 1996 CHEVROLET TRUCK
  • 5.0L
  • V8
  • 2WD
  • AUTOMATIC
  • 170,000 MILES
Have changed plugs, wires, aic valve, egr valve, cleaned mass airflow sensor and throttle body. Still Idles very rough and a lot worse when in gear. Much better when accelerating. Please help.
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Sunday, January 5th, 2020 AT 5:58 PM (Merged)
Tiny
OBXAUTOMEDIC
  • MECHANIC
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Hello,

Ok, unless you forgot to mention it you didn't replace the Distributor Cap & Rotor.

I would remove the cap and take a look inside if the electrodes are corroded or worn down replace both.
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Sunday, January 5th, 2020 AT 5:58 PM (Merged)

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