Rough Idle when engine goes under 1000 RPM

sahdct · Post by **sahdct** » 22 Jan 2011, 21:08

2001 V70.

MAF has been cleaned, new plugs, and ETM were tested and runs within limits. Throttle body was cleaned( well wiped by a tec. they say). We had the car checked and of course nothing found.

Here's what's going on. Warm the car up. While car is in N, you rev. it to 3000 RPM. As it goes below 1000 rpm to say 800 all of a sudden we get a rough idle, goes up 1000 Rpm and then feels OK till you do the same thing again. This doesn't occur all the time. When you rev the engine and it gets to this "coughing" point the car's lighting dims and then brightens again.

While driving as you slow down the rpm drops to just below 1000 to 800 rpm you get a little shake then it goes away. There is no wild swing in RPM with a bad ETM. We do notice that there seems to be a louder exhaust noise coming from the catalitac(sp) converter section.

Any thoughts. I don't have a code reader.

jnagano89 · Post by **jnagano89** » 23 Jan 2011, 19:25

have you had the pcv system checked? If it is clogged or there is no vacuum on the system it can cause a rough idle condition

sahdct · Post by **sahdct** » 23 Jan 2011, 20:16

Check for PCV pressure and its good. It either vac. lack or still the MAF. I sprayed carb cleaner following the intake to the manifold, but nothing was happing or I'm just checking it incorrectly.

tcatlanta · Post by **tcatlanta** » 09 Apr 2011, 20:09

if you lift the oil fill cap and feel a strong vaccume, it is the flame trap or Pcv system. this soln also stopped an oil leak at the cam seal.

Post by **VCA** » 11 Apr 2011, 06:10

sahdct wrote:This doesn't occur all the time. When you rev the engine and it gets to this "coughing" point the car's lighting dims and then brightens again.

Wait, when the engine drops to 800 and it coughs, the lights dim?! How significantly do they dim? I'm thinking an intermittent charge controller in the alternator could cause that. Everything on these cars rely on a good source of electricity, so if something like the alternator's putting out bad current (or there's a bad ground causing the alternator to be unable to charge the battery/electrical system), that could definitely cause these symptoms. Do you have a volt-ohm meter?