I have a 1999 1500 with a 5.9L. When it's cold, the idle feels rough, almost like it's missing just a tiny bit. When it warms up it gets better but still does it now and then.

I have new plugs (V-Powers), wires (Advance Auto Parts standard), cap and rotor. I've taken off and cleaned the throttle body, there's no oil residue in the intake, no vacuum leaks that I can discern. I've replaced the "Wild Vents" check valve and a smaller check valve under the TB, as well as the PCV valve. The wires are routed per the TSB (as near as I can tell, but I had that done at a shop when they were running a diagnostic trying to figure out the idle problem).

They said that the slightly rough idle was normal for this engine as it's externally balanced. Why would it be worse when the engine is cold?

Any ideas?

 

Ignition coil?

 

Hmmm... could be. That would be an easy fix. I may pick one up.

 

Here is what the FSM says (at least the coil theory is a possible cause according to the FSM):

ENGINE STALLS OR ROUGH IDLE
1. Carbon build-up on throttle plate 1. Remove throttle body and
de-carbon. (Refer to 14 - FUEL
SYSTEM/FUEL INJECTION/
THROTTLE BODY - REMOVAL).

2. Engine idle speed too low 2. Check Idle Air Control circuit.
(Refer to 14 - FUEL SYSTEM/FUEL
INJECTION/IDLE AIR CONTROL
MOTOR - DESCRIPTION)

3. Worn or incorrectly gapped spark
plugs 3. Replace or clean and re-gap
spark plugs (Refer to 8 -
ELECTRICAL/IGNITION CONTROL/
SPARK PLUG - CLEANING)

4. Worn or burned distributor rotor 4. Install new distributor rotor

5. Spark plug cables defective or
crossed5. Check for correct firing order or
replace spark plug cables. (Refer to
8 - ELECTRICAL/IGNITION
CONTROL/SPARK PLUG CABLE -
DIAGNOSIS AND TESTING)

6. Faulty coil 6. Test and replace, if necessary
(Refer to 8 - ELECTRICAL/
IGNITION CONTROL/IGNITION
COIL - REMOVAL)
BR/BE ENGINE 5.9L 9 - 119
ENGINE 5.9L (Continued)

7. Intake manifold vacuum leak 7. Inspect intake manifold gasket
and vacuum hoses (Refer to 9 -
ENGINE/MANIFOLDS/INTAKE
MANIFOLD - DIAGNOSIS AND
TESTING).


When it comes time to replace my coil, this is the one I am going to buy. http://www.partsamerica.com/ProductD...pe=190&PTSet=A

 

Or you can run down to O'Reillys, pick up a MSD Blaster 2, run to Menards, grab a couple of hose clamps, two bolts, and two nuts, and mount it to the stock mounting location.

 

Do you feel that there would be a significant advantage with the MSD Blaster 2 over the MSD stock type? Not disagreeing, just trying to educate myself.

MSD 8228 (OEM type)
Coil Specs
Turns ratio: 70:1
Primary resistance: 1.2 OHMs
Secondary resistance: 13.7K OHMs
Inductance: 3.9mH
Maximum voltage: 40,000 Volts
Peak current: N/A
Spark duration: N/A
Weight: N/A

MSD 8202 (blaster 2)
Coil Specs
Turns ratio: 100:1
Primary resistance: .7 OHMs
Secondary resistance: 4.5K OHMs
Inductance: 8 mH
Maximum voltage: 45,000 Volts
Peak current: 140 mA
Spark duration: 350 uS
Weight: N/A

 

I replaced the coil on it-- still missing. I then rechecked the gap on the plugs-- some were .035, some .040, so I corrected that. Still missing. Next I ran the crankcase pressure test desccribed in the plenum gasket TSB-- no problems there, no vacuum in the crankcase. I connected the gauge to the intake manifold and vacuum held steady right in the middle of the "green zone" on the vacuum gauge. I guess I'm stumped.

Would either of those tests show if I have a cracked head? I have no oil in the coolant, coolant in the oil, or bubbling in the coolant. I don't have oil consumption that I've detected yet (only put 1500-2000 miles on it but the oil level hasn't changed).

GRRRRRRR!!!!

 

Do you hear any valve "ticking" sounds when the engine is idling?
Do you hear more or less valve noise when engine is cold compared to warm?

 

well a bad or dirty iac will idle a little rough, but most of the time the iac will cause rought ilde when the motors is warmed up.,, so it's just a thought. may want to check. it's free to clean it.

 

I don't hear any valve ticking cold or warm. I cleaned the IAC and the throttle body right after I got the truck (approx 3 wks). It was nasty. I suppose the IAC could be on it's way out.

Is this engine supposed to have a little bit of a shake like an occasional mild miss at idle? My dad told me that it's supposed to be that way because it's externally balanced and because of the cam that's in it.

:/

I doubt this could be related but there is a small exhaust leak where the exhaust pipe goes into the muffler. I just haven't gotten around to getting it welded yet. This leak is after the cat and downstream O2 sensor.