rough idle

[LaGrasta]

I just replaced dizzy, full spider/pump. 241k on motor, very well maintained. Everything has been checked out, tuned-up and cleaned. So I'm struggling to find what else it could be. Idles poor, more so in park, but never stalls.
My next step was to inspect hoses for a vacuum leak. Also, the coil has never been replaced. It runs and drive great so probably not the coil. Suggestions please.

[MountainManJoe]

My next step was to inspect hoses for a vacuum leak

don't forget the notorious intake gasket.

wouldn't hurt to measure fuel pressure.

[LaGrasta]

thanks Joe. It has a new intake gasket, and new OEM fuel pump too so I expect pressure is also good.

[MountainManJoe]

bad catalytic converter?

[LaGrasta]

sheesh, I'm still struggling with this idle condition. I spent nearly $2k on this! New OEM spider, pump, and dizzy. I just installed an aftermarket Air Idle Control valve, no change. What next, any new suggestions? I do have a P300 code as well.

[Astrophysics]

Hi,

242,000 miles. That is great.

1. Check vacuum
2. Check electrical grounds at studs
3. Check fuel pressure
4. Check O2 sensor readings on OBD 2 scanner running real time data
5. Clean throttle body gate with special spray
6. Check compression at spark plug holes with WOT, wide open throttle
to look for ring or valve leak

Good luck

AP

[Astrophysics]

Hi

Also, try OEM air filter instead of K&N

AP

[Astrophysics]

Also,

11. Spark plugs and cables

12. Cap and rotor for cracks and carbon arc tracks

[LaGrasta]

hmmm, of the suggestions, these are the only things I haven't explored:
1. Check vacuum
2. Check electrical grounds at studs
4. Check O2 sensor readings on OBD 2 scanner running real time data
6. Check compression at spark plug holes with WOT

[WoodButcher]

hmmm, of the suggestions, these are the only things I haven't explored:
1. Check vacuum
2. Check electrical grounds at studs
4. Check O2 sensor readings on OBD 2 scanner running real time data
6. Check compression at spark plug holes with WOT

How in hell do you do #6?
Every time I have done a compression test I'll pull the fuel pump relay so the engine will not fire, just turn over to build pressure in the cylinder that I wish to read.

[MountainManJoe]

yeah if the engine is running (especially @ WOT), wouldn't that just blow the ass out of your pressure gauge?