Rough idle when cold
12-18-2002, 05:23 PM
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Rough idle when cold
The '84 has a funny problem going on when cold. The car idles roughly at 850-900 rpm. After a few minutes (3-5) the roughness goes away but the idle still sits at 850-900 rpm with about a 50 rpm "hunt" that is probably a small vacuum leak. Could this be a sign of a bad motor mount ?
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12-18-2002, 06:17 PM
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Start with the easy stuff:
- Check all the hard black plastic vaccuum line for cracks/abrasion holes. Replace as necessary.
- Mity-Vac all the vacuum accessories and basically check for other vaccuum leaks
- Set the idle speed per the service docs - all electrical accessories off, idle air regulator disabled, possibly O2 unplugged (I forget), automotive multimeter on the coil and set to "low tach" range for exact reading, and I think the spec is 850+/- 50 rpm.
- If it still hunts around, you probably need the CO set. You can't really do it with the O2 sensor. You need a real CO meter. I bought one off eBay. It needs calibrated so I'm working on this issue now.
With the engine in good mechanical shape and no vacuum leaks, the correct idle speed and CO setting should result in a rock solid idle.
Even with good mounts, if the idle dips too low you'll feel it vibrate the car a little.
Bryan
"At Porsche, we only make sports cars"
- Check all the hard black plastic vaccuum line for cracks/abrasion holes. Replace as necessary.
- Mity-Vac all the vacuum accessories and basically check for other vaccuum leaks
- Set the idle speed per the service docs - all electrical accessories off, idle air regulator disabled, possibly O2 unplugged (I forget), automotive multimeter on the coil and set to "low tach" range for exact reading, and I think the spec is 850+/- 50 rpm.
- If it still hunts around, you probably need the CO set. You can't really do it with the O2 sensor. You need a real CO meter. I bought one off eBay. It needs calibrated so I'm working on this issue now.
With the engine in good mechanical shape and no vacuum leaks, the correct idle speed and CO setting should result in a rock solid idle.
Even with good mounts, if the idle dips too low you'll feel it vibrate the car a little.
Bryan
"At Porsche, we only make sports cars"
