Rough idle, engine miss at medium throttle

Tiny
SAINTMARYSJOHN
  • MEMBER
  • 1999 CHEVROLET S-10
  • 6 CYL
  • 2WD
  • MANUAL
  • 185,000 MILES
Problem started when I channed plugs. When under part or full throttle, engine bogs down and if the accelerator is reduced a little, it returns to running well. Also happens at full throttle. I changed the plugs again, replaced the igmition coil, and plug wires, along with the fuel filter. The fuel pump is only 25,000 miles old. I also swapped the MAF in the air cleaner entry port. I get no codes on the OBD II scanner and all tests I have run come up with no problem. Seems to be very similar to codyirelan545 problem entered on 17 Sep. When I filled the truck the last 3 times, I am getting 27+ MPG. Any suggestions would be greatly appreciated.
Sunday, September 19th, 2010 AT 7:33 PM

46 Replies

Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Hi saintmarysjohn, Welcome to 2carpros

Lack of acceleration,chugging,hesitating,jerking,bogging,misfiring etc. could be caused by one of the following below: I know its a long list to check, what makes it hard there's no CEL, no starting point-But you can try the TPS and MAP sensors and the fuel pressure for a starter

This guide will help us find it

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

Please run down this guide and report back.

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Sunday, September 19th, 2010 AT 9:18 PM
Tiny
JASON GHORMLEY
  • MEMBER
  • 8 POSTS
  • 1998 CHEVROLET S-10
  • 2.2L
  • 4 CYL
  • 2WD
  • MANUAL
  • 282,392 MILES
Just replaced all of the o2 sensors and exhaust gaskets. Because it had a p1133 code truck runs good with a rough idle when coming to a stop I have not replaced the timing yet. What could cause that idle to go 880 rpm to 920 rpm with no vacuum leaks.
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Monday, June 29th, 2020 AT 7:01 PM (Merged)
Tiny
SATURNTECH9
  • MECHANIC
  • 30,870 POSTS
How did you look for vacuum leaks?
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Monday, June 29th, 2020 AT 7:01 PM (Merged)
Tiny
JASON GHORMLEY
  • MEMBER
  • 8 POSTS
I hooked up the vacuum gauge to the power boosters and saw that I was at 22 in of mercury. And then I sprayed wd40 over vac lines, and did not find any engine conditions changing. Hooked up the fuel gauge to fuel rail, and found that I had 39psi to the fuel rail at key on engine off. And Then hooked up the t-gauge to where the fuel flitter was, and found that I had 30psi to it.
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Monday, June 29th, 2020 AT 7:01 PM (Merged)
Tiny
SATURNTECH9
  • MECHANIC
  • 30,870 POSTS
I have never seen it done that way one way is to watch the fuel trim on a scan tool and spray carb spray all over watching the fuel trims. The best way to find even the smallest leaks is with smoke.
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Monday, June 29th, 2020 AT 7:01 PM (Merged)
Tiny
MACAAH
  • MEMBER
  • 1 POST
  • 1998 CHEVROLET S-10
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 177,000 MILES
Why is my truck idling rough after I have changed the spark plugs and the altenator
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Monday, June 29th, 2020 AT 7:01 PM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Engine running rough or misfiring can be cause by the following:

1. Defective spark plug.
2. Inadequate spark/coil, defective spark plug wire.
3. Lack of compression
4. Vacuum leak
5. Fautly fuel injectors.
6. Insufficient fuel pressure.
7. Contaminated fuel.
8. EGR valve that is leaking.
9. Oxygen sensors.
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Monday, June 29th, 2020 AT 7:01 PM (Merged)
Tiny
LEWKEV92
  • MEMBER
  • 1 POST
  • 1996 CHEVROLET S-10
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 176,000 MILES
I have a 96 chevy s10 truck with the 262 4.3 vortec engine. I had it put in the shop for a burnt valve on the number 1 clinder and lifters knocking on the #2 and #6 cylinder, so I had the heads reworked on it. Now the engine runs fine at idel but when you get the rpm's up to about three grand the #6 lifters start knockin and the engine sounds like it wants to quit the whole time unless it's at an idel. It has no power at all and it will not climb a hill period. And my quetion is what do you think is wrong with this engine.
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Monday, June 29th, 2020 AT 7:02 PM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Sounds like you need to have the camshaft checked if the valve lifters are replaced and the rocker arm nuts are torque to specs-camlobes could be worned
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Monday, June 29th, 2020 AT 7:02 PM (Merged)
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Depending on how loud hte knocking is it may be activating the kock sensor andit's cutting the power back. Check the oilpressure by manual gauge. Make sure the rockers are adjusted though as well. They may notbe.
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Monday, June 29th, 2020 AT 7:02 PM (Merged)
Tiny
JACOBBELL
  • MEMBER
  • 1 POST
  • 1995 CHEVROLET S-10
  • 4 CYL
  • 2WD
  • MANUAL
  • 229,020 MILES
I just bought the truck for 400 dollars, it was missing on cylinder 4 so the person that I bought it from said. I went and changed out the plugs and wires along with the coil that was not already changed. The missing is not there any longer. When I take off it bogs way down unless I give it pretty much all the pedal. Is this because of a compression problem or is it a simple fix
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Monday, June 29th, 2020 AT 7:02 PM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Inspect and test all the following listed below and get back with some testing results we start here

Oxygen sensors.
Catalytic converter.
Fuel injectors dirty/sticking.
Mass airflow sensor/Airflow meter.
Throttle position sensor.
Manifold absolute pressure sensor.
EGR Valve
Fuel pressure regulator leaking or defective fuel pump.
False air leakage.
Fuel contamination.
Foul/defective spark plugs.
Open spark plug wires.
Ignition coil/Coil packs defective.
Incorrect ignition timing.
Cap and rotor.
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Monday, June 29th, 2020 AT 7:02 PM (Merged)
Tiny
JARRELLG
  • MEMBER
  • 1 POST
  • 1994 CHEVROLET S-10
  • 4.3L
  • V6
  • 2WD
  • AUTOMATIC
  • 275,000 MILES
I've had the truck for about 7 months. Rough idle since I got it. Found several vacuum leaks and fixed them. Replace the EGR, plugs, wires, cap, rotor and MAP sensor. Cleaned the TBI and replaced all gaskets and pressure regulator diaphragm and spring. Replaced the PCV and have blown out all vacuum ports and lines with carb cleaners and have not found any blockage. Lately, the truck has gotten worse and will hardly idle until it warms up and now, there is no power during acceleration until fully warmed up. Works better when I manually shift thru the gears allowing the engine to get higher RPM's. When on the highway, it would get up to speed but seems to take more time than at first. It doesn't have any power to pass other traffic on inclines in the mountains.
During idle, running very rich and can smell fuel.
Any ideas?
Jarrell
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Monday, June 29th, 2020 AT 7:02 PM (Merged)
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Check fuel pressure with a gauge may below. If that is ok then it may be the injection unit has gone bad if it's cpi injection. If throttle body injection check for a vacuum leak at bottom of tbi unit they like to blow gaskets there.
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Monday, June 29th, 2020 AT 7:02 PM (Merged)
Tiny
CARI365
  • MEMBER
  • 2 POSTS
  • 1993 CHEVROLET S-10
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 102,000 MILES
Hello, I have a 1993 chevy S10 blazer with 102,000 miles that idles very rough at a stand still, but under power runs okay. I have replaced the fuel injectors, replaced the oxygen sensor, cleaned the egr, cleaned the throttle body, cleaned the plantum, cleaned the idle air control (that was very dirty), checked the charcol canister for fuel in it, it was okay, check spark plug wires for arching they were fine, put blazer on a scanner and came up with a rich fuel code which was a 44. No engine light or codes other than rich fuel. You can also smell a strong fuel smell especially when you first start the blazer then it seems to clear up. Im stumped. Would greatly appritiate your advice on what you think could be the problem
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Monday, June 29th, 2020 AT 7:02 PM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Check the fuel pressure and get back with the readings
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Monday, June 29th, 2020 AT 7:02 PM (Merged)
Tiny
CARI365
  • MEMBER
  • 2 POSTS
Hi, Im not able to get the fuel pressure readings the guy who has the tester is in the hospital. Could the problem be the cataltic converter. It has a very strong fuel odor, I did have replace all the fuel injectors if that helps.
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Monday, June 29th, 2020 AT 7:02 PM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Could be disconnect the exhaust pipe on the exhaust manifold and hang it aside and try it again and see if it goes
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Monday, June 29th, 2020 AT 7:02 PM (Merged)
Tiny
FRED H.
  • MEMBER
  • 1 POST
  • 1993 CHEVROLET S-10
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 140,000 MILES
My truck has been idleing rough for about a month now. It has gotten progressivly worse. It used to run rough only when the a/c was on but we replaced the idle control and the problem was solved for about 4 months. Here's the first problem- now it runs very rough when I am stopped or with no foot on the gas at idle speed. Almost stalls when you come to an adrupt stop. When you do a steady speed the truck runs perfect. Second problem is if the a/c is on, still runs rough but the a/c will quit blowing completly when you try to pass someone or stomp the gas, then resume cold when you let off or maintain speed. To let you know something else-the truck has ALWAYS had blue smoke on start up. The temp gauge reads even and no problem lights come on, no other signs or symptoms that I can make you aware of. The truck runs the same rain or shine, hot or cold weather.
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Monday, June 29th, 2020 AT 7:02 PM (Merged)
Tiny
MERLIN2021
  • MECHANIC
  • 17,250 POSTS
You have a vacuum leak in the A/C vacuum supply line! This is the black line that goes thru the firewall, trace it to either the break, or the check valve and reserve tank, that could be cracked. Fix the vacuum leak and both a/c and idle will improve, the blue smoke is burning oil. If only at startup, it's probably valve stem seals.
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Monday, June 29th, 2020 AT 7:02 PM (Merged)

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