erratic idle at stop
 

This started 2 days ago. I am driving at normal speeds 60 to 70 with no trouble. Then when I have to slow down to an idle or a stop the engine wanted to stall. It has stalled 2 times already today. I have checked the battery and partly the altenator. The battery is showing 12.5+-volts and the altenator shows that it is charging at 13v. I have had this happen with other vehicles and it was either the battery or altenator. Any ideas?

Does it take a long cranking time to start? The last time I had a 2001 S40 give me idle trouble it was a bad fuel pressure regulator.

The Fuel pressure regulator could certainly be a problem, it's relatively easy to check it. For mine the end of the little hose had split and it wasn't holding pressure.

You should also check the condition of the Idle air control valve, which is nice and easy to get to, just off the air intake. Unbolt it and fill it w/ Gas or Carb cleaner and let it soak for 10 or so, it should come away sparkling clean. While you're in that area, you might as well clean the throttle plate too.

sparkplugs and cables? how used are they?

Now the engine light is on. And it stalled at a stop light again. At normal speeds the car runs OK. Only when I am coming to or at a stop at low rpm. I will check the air contral valave, clean the throttle plate. Any other good ideas.

If you're having trouble when you start, as was suggested before the fuel pressure regulator could be the culprit. If you remove the guard to the right of the fuel rail you should see it. It's a plastic/metal piece sticking out of the fuel rail with 1 hose running to it. look at the quality of that small rubber hose end. Mine was cracked, and starting to tear, this caused an erratic idle and (because it was losing fuel pressure) it would be unpredictably hard to start when it had sat for much more than 10 minutes.

The IACV (Idle air control valve) is a very good starting point however. check the integrity of the gasket while you're looking at it, if the gasket isn't sealing very well, that alone could be a source of the problem, though that generally leads to a very high idle. This sounds likely that the IACV is involved here somehow. If your issue is only occurring at idle, or when your foot isn't on the gas at low RPMs You're getting air through the IACV, not the throttle plate.

You could also check for vacuum leaks (you can use either a mister bottle full of water, or a can of throttle body/carb cleaner and misting the vacuum hoses to see if there's a leak anywhere, though that again would normally be the cause of a high idle rather than low, but still worth taking a look.

My 04 XC90 does the same thing. i went to the dealer and they said the code read throttle body malfunction. They wanted to clean the throttle body for a mere 350$$!!!!. the tech said it might work, it might not. The best thing to do would be to replace the unit. 550$$ for a new throttle body, not including labor. Tried throttle body cleaner with no luck. Good luck

I cleaned the IACV with gas and it was leaking thru the valve from one side to the other. So I am replacing it. $205 w/out the gasket. I hope this fixes the problem.

After cleaning it, did you replace the IACV and start the car? It's just supposed to be a pass through for air, but as it's part of the intake, it can become clogged with dirt etc. which makes it incapable of working properly. Also check the electrical connection to the IACV, if you can, cleaning it with isopropyl alcohol and smearing it with dielectric grease is a good plan. I would recommend, across the board, when you replace the IACV or, for that matter, any other part that involves a gasket and significant pressure, replace the gasket too.

If the CEL is on in the car, I'd certainly take it to Advance Auto and get that read asap, would go a long way toward accurately diagnosing the problem. Where are you getting a new IAC that it's over 200 btw? www.autopartswarehouse.com has an OES Genuine IACV for 160

I payed 280 for mine for an '01 Subaru Outback, but that's a whole different beast all together.

I want ot say thanks to the people that helped with my cars problem. It was the IACV. I replaced it and now its running normal. I sure I will have questions for you all next time the car has issues. So thanks.