91 K1500 5.7 rough idle

powellsd · 10-27-2009, 04:30 PM

Ok i have a 91 k1500 with the 5.7 and i been having a sporadic idle after it warms up. I have researched it all over the place but havent really found anything that is leading me to the right direction. The truck has 188k on it and i pretty much replaced all maint items on it. I am getting it ready for winter and some hunting trips. Here is what i have replaced.

ICV, Cap, Rotor, Plugs, Wires, Coil, EGR, EGR Sensor, TPS, ICM, Fuel Reg, Fuel Pres is 11psi, Oxygen Sens, all vacuum lines, Fuel Filter, Did a vac test and no leaks from the smog machine, Ground wires in engine bay look good. Putting out 14-15v on the battery.

Ran a can of BG44k in gas, Seafoam in crankcase.

I am getting a good spray from the injectors at idle and when i rev the engine.

I have a new temp sensor and tstat but cant think that would cause my issues.

Anyone have some ideas on this?

I do smell gas fumes (more then one would think) when i take the air cleaner cover off...like it is overloading itself.

bradrhale · 10-27-2009, 08:24 PM

when you did the vac test, was it at operating temps or when still cold?? you mention a new temp sensor but did not say that you had already put it on. just for clarification.
how does the throttle body look?? dirty and plagued with carbon deposits?? clean??

powellsd · 10-27-2009, 08:36 PM

Quote:

Originally Posted by bradrhale

when you did the vac test, was it at operating temps or when still cold?? you mention a new temp sensor but did not say that you had already put it on. just for clarification.
how does the throttle body look?? dirty and plagued with carbon deposits?? clean??

Sorry did the vac test after it was warmed up. No i havent installed the new temp sensor yet, the TB looks good and i sprayed it down with carb cleaner.

I am gonna try to see if i can get my buddy scanning tool and hook it up to the truck as we are driving around. I did the check engine light code trick and that came up clean...

gmctrucks · 10-28-2009, 01:36 AM

Here I go again try a can of Seafoam the stuff really works good it might clean them injectors and leave them new again.

chadwickthomas · 10-28-2009, 03:59 AM

when your engine is ideling and your moter is steady reving up and down at a pretty steady pace you need to unscrew your idle step up motor out of the side of your throttle body and clean the pendelum and port it screws into.IF it fluctuates slightly but runs real rough you have a vacuum leak somewhere check your intake manifold for leakage with eather but more likely it will be your egr valve pendelum not seating closed due to carbon build up in the ports.Also make shure under you throttle body is not clogged up with carbon if it is check vacuum ports comming out of throttle for carbon restrictions

leolkfrm · 10-28-2009, 04:24 AM

I don't see a fuel filter on the list?

powellsd · 10-28-2009, 06:34 AM

Quote:

Originally Posted by gmctrucks

Here I go again try a can of Seafoam the stuff really works good it might clean them injectors and leave them new again.

I used a can BG44k and no dice..

Quote:

Originally Posted by chadwickthomas

when your engine is ideling and your moter is steady reving up and down at a pretty steady pace you need to unscrew your idle step up motor out of the side of your throttle body and clean the pendelum and port it screws into.IF it fluctuates slightly but runs real rough you have a vacuum leak somewhere check your intake manifold for leakage with eather but more likely it will be your egr valve pendelum not seating closed due to carbon build up in the ports.Also make shure under you throttle body is not clogged up with carbon if it is check vacuum ports comming out of throttle for carbon restrictions

I will look at that. Its not rough while driving just at idle

Quote:

Originally Posted by leolkfrm

I don't see a fuel filter on the list?

Sorry i changed the fuel filter.

jremington59 · 10-28-2009, 11:01 AM

I have the same motor in a 94 and I've had the same problem forever to the point that I've given up trying to fix it, lol....

I do have a bad exhaust donut with a bad leak and someone told me this can mess up the readings from the 02 sensor. Is your exhast bad at all in front of the sensor?

One other thing Im wondering about is a worn cam....

batty1214 · 10-28-2009, 09:39 PM

If you havent already, Pull the cap and rotor off of the distributor, and move the drive rod...... It's normal for it to move up and down a bit, but any side to side play will make it miss........ Also, the drive gear of the distribtor may be a little worn, and not letting it run like it should.... Thats what it ended up being on my work truck.....

powellsd · 10-28-2009, 09:42 PM

Quote:

Originally Posted by batty1214

If you havent already, Pull the cap and rotor off of the distributor, and move the drive rod...... It's normal for it to move up and down a bit, but any side to side play will make it miss........ Also, the drive gear of the distribtor may be a little worn, and not letting it run like it should.... Thats what it ended up being on my work truck.....

I thought about getting a new distributor for it, but looking at a couple of things first..

Thanks for the tip

10-27-2009, 04:30 PM	#1
powellsd Junior Member Join Date: Oct 2009 Posts: 5	91 K1500 5.7 rough idle Ok i have a 91 k1500 with the 5.7 and i been having a sporadic idle after it warms up. I have researched it all over the place but havent really found anything that is leading me to the right direction. The truck has 188k on it and i pretty much replaced all maint items on it. I am getting it ready for winter and some hunting trips. Here is what i have replaced. ICV, Cap, Rotor, Plugs, Wires, Coil, EGR, EGR Sensor, TPS, ICM, Fuel Reg, Fuel Pres is 11psi, Oxygen Sens, all vacuum lines, Fuel Filter, Did a vac test and no leaks from the smog machine, Ground wires in engine bay look good. Putting out 14-15v on the battery. Ran a can of BG44k in gas, Seafoam in crankcase. I am getting a good spray from the injectors at idle and when i rev the engine. I have a new temp sensor and tstat but cant think that would cause my issues. Anyone have some ideas on this? I do smell gas fumes (more then one would think) when i take the air cleaner cover off...like it is overloading itself. Last edited by powellsd; 10-28-2009 at 06:34 AM.

10-28-2009, 04:24 AM	#6
leolkfrm Senior Member Join Date: Mar 2008 Location: N.Y. Posts: 4,300	I don't see a fuel filter on the list? __________________ 4 wheels move the body 2 wheels move the soul B.W.A.I

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10-27-2009, 08:24 PM	#2
bradrhale Senior Moderator Join Date: Apr 2006 Location: Texas Posts: 8,030	when you did the vac test, was it at operating temps or when still cold?? you mention a new temp sensor but did not say that you had already put it on. just for clarification. how does the throttle body look?? dirty and plagued with carbon deposits?? clean??

10-28-2009, 01:36 AM	#4
gmctrucks Senior Member Join Date: Nov 2006 Location: Houston,Texas Posts: 4,035	Here I go again try a can of Seafoam the stuff really works good it might clean them injectors and leave them new again.

10-28-2009, 03:59 AM	#5
chadwickthomas Junior Member Join Date: Oct 2009 Posts: 11	when your engine is ideling and your moter is steady reving up and down at a pretty steady pace you need to unscrew your idle step up motor out of the side of your throttle body and clean the pendelum and port it screws into.IF it fluctuates slightly but runs real rough you have a vacuum leak somewhere check your intake manifold for leakage with eather but more likely it will be your egr valve pendelum not seating closed due to carbon build up in the ports.Also make shure under you throttle body is not clogged up with carbon if it is check vacuum ports comming out of throttle for carbon restrictions

10-28-2009, 11:01 AM	#8
jremington59 Full Member Join Date: Oct 2009 Posts: 29	I have the same motor in a 94 and I've had the same problem forever to the point that I've given up trying to fix it, lol.... I do have a bad exhaust donut with a bad leak and someone told me this can mess up the readings from the 02 sensor. Is your exhast bad at all in front of the sensor? One other thing Im wondering about is a worn cam....

10-28-2009, 09:39 PM	#9
batty1214 Senior Member Join Date: Nov 2008 Location: Vernal Utah Posts: 1,135	If you havent already, Pull the cap and rotor off of the distributor, and move the drive rod...... It's normal for it to move up and down a bit, but any side to side play will make it miss........ Also, the drive gear of the distribtor may be a little worn, and not letting it run like it should.... Thats what it ended up being on my work truck.....