Idle issues

[Lvnmarks]

Well after a new (used 147K) engine, new intake/oil pan/valve cover/EGR/Throttle body gaskets, new IAC, new spark plugs and a mess of other new stuff I'm still having a rough idle and periodic hesitation on acceleration.

When I replaced the intake manifold a few weeks ago I had brand new plugs in the heads and after the intake was installed I had a code for a bad coil and a miss fire on #8. I replaced to coil but still had a very small miss. Since then I have about 300 miles on it and warm or cold she idles rough like a cylinder is dropping out and the miss has gotten much worse. This is definitely an ignition problem, I'm just not sure what else to check.

Had no codes after I replaced the coil but I will run a scan tonight when I get home.



So my question is what else can I be looking at?

One other observation I have is when I'm going to start it cold (not always) it just cranks and cranks, turn the key back off and back to on (let the fuel pump prime) then she starts right up. I'm guessing that might be the CPS though.

 

[driller]

AllData shows a TSB (TSB 05-22-8) for diagnosing cylinder specific misfires.

Basically it's either fuel or spark.

Misfire Definition:
A misfiring cylinder is lacking power relative to the other cylinders. The causes for a cylinder specific misfire could be fuel, spark, or mechanical problems.

Perform a thorough visual inspection. If no visible concerns are found use the following WDS tools for misfire diagnosis:

• Self-test (Check for codes first)
• Power Balance (Identify the cylinder of concern)
• Relative Compression (Rule out a possible mechanical issue)
• Fuel (Make sure fuel injectors are not restricted)
• Ignition (Make sure spark plugs and coils are working properly)
• Oscilloscope (Detailed signal analysis)

 

[Lvnmarks]

Got home and pulled the codes, looks like #5 is missing now. I'll change the coil on that later tonight and see what happens. I'll throw the pressure gauge on there as well to see if there is any reason to suspect compression.



After I cleared the PCM




For clarification it's...


Fire wall
4 8
3 7
2 6
1 5
Radiator

 

[driller]

Without just throwing parts at it (or having an oscilloscope), the only thing left is swapping coils/injectors to see if the fault follows.

 

[Lvnmarks]

This is from this morning....



I didn't get a new coil on it last night but did look at it for a few minutes. Apparently the threads in the new intake are spinning thus not holding the coil properly. I'm going to have to get fancy with some zip ties later, I'll throw another coil and new plug in there tonight.

My new question is what's going on with my O2 sensor? These are all relatively new (>10K)

 

[Lvnmarks]

Replaced the coil on #5 and the misfire has changed, it's no longer isolated to one cylinder. It might be the cold but after a cold start up the idle will slowly decrease 500 rpm, 400 rpm, 300 rpm, 200 rpm, then die. I can give the throttle a blip but the rpm will still come down until the engine is warmed up.

Here is the most recent scan...

 

[tixer]

The last three times I've seen "this car won't idle until it is warm," it has been upper intake manifold gasket leaks.. Three different cars, but one of them was yours... I'm not saying that is the problem, but it may be worth double-checking your work..

Check the clamps on the air intake, too.. I made that mistake once.. It's easy to do after taking everything apart and wanting to test.

 

[Lvnmarks]

Well Mike you were close, I found the little elbow in the PCV line to be cracked and sucking in un-metered air. She seems to be running better now but I'll give it a few days and check for codes again.

I got an awesome deal on a Gen II, 250 amp, Powermax Alternator, so I installed it. Which took care of my squeaky engine sound and my head lights no longer dim when idling. I'm hoping that might help to increase the life of the ignition coils as well.