rough idle

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LaGrasta
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rough idle

Post by 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.
1998 Astro, 246,000 miles

K&N air filter
TruCool trans cooler
2" Overland lift & 15" BFG Terrain, 3.73 gears
JET Performance SCU-2000 (Speed Control Unit)
Gabriel Ultra shocks, rear AirLift bags & sway bar
Draw-Tite Dual Port Hitch System, hitch-mounted bike rack (4), hitch-mounted cargo tray, Thule roof-mounted cargo box
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MountainManJoe
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Re: rough idle

Post by 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.
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LaGrasta
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Re: rough idle

Post by LaGrasta »

thanks Joe. It has a new intake gasket, and new OEM fuel pump too so I expect pressure is also good.
1998 Astro, 246,000 miles

K&N air filter
TruCool trans cooler
2" Overland lift & 15" BFG Terrain, 3.73 gears
JET Performance SCU-2000 (Speed Control Unit)
Gabriel Ultra shocks, rear AirLift bags & sway bar
Draw-Tite Dual Port Hitch System, hitch-mounted bike rack (4), hitch-mounted cargo tray, Thule roof-mounted cargo box
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MountainManJoe
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Re: rough idle

Post by MountainManJoe »

bad catalytic converter?
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LaGrasta
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Re: rough idle

Post by 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.
1998 Astro, 246,000 miles

K&N air filter
TruCool trans cooler
2" Overland lift & 15" BFG Terrain, 3.73 gears
JET Performance SCU-2000 (Speed Control Unit)
Gabriel Ultra shocks, rear AirLift bags & sway bar
Draw-Tite Dual Port Hitch System, hitch-mounted bike rack (4), hitch-mounted cargo tray, Thule roof-mounted cargo box

Astrophysics
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Re: rough idle

Post by 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

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Re: rough idle

Post by Astrophysics »

Hi

Also, try OEM air filter instead of K&N

AP

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Re: rough idle

Post by Astrophysics »

Also,

11. Spark plugs and cables

12. Cap and rotor for cracks and carbon arc tracks
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LaGrasta
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Re: rough idle

Post by 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
1998 Astro, 246,000 miles

K&N air filter
TruCool trans cooler
2" Overland lift & 15" BFG Terrain, 3.73 gears
JET Performance SCU-2000 (Speed Control Unit)
Gabriel Ultra shocks, rear AirLift bags & sway bar
Draw-Tite Dual Port Hitch System, hitch-mounted bike rack (4), hitch-mounted cargo tray, Thule roof-mounted cargo box
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Re: rough idle

Post by WoodButcher »

LaGrasta wrote: Tue Apr 05, 2022 8:08 am 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.
'93 Safari shorty, 350 swap
'05 Astro AWD, lifted, 6 liter, cammed, ported and programmed for fast.
'69 G10, straight 6, 3 onatree, jumped at me when I had a pocketful of cash looking for a spare astro. :)
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Re: rough idle

Post by MountainManJoe »

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