Engine RPMs sometimes drops too low briefly after stopping

danerrr808 · Post by **danerrr808** » 09 Aug 2007, 04:16

Hi,

I own a 1998 S70 that seems to drive fine.

Once in a while, as soon as the car comes to a full stop the RPMs quickly dip down to 300, causing the engine to sputter just for a second, before the RPM slowly rises and idles back at 900 as normal. This only happens once every few days, I live in Hawaii were the temperature is always warm, and I am not hitting any bumps in the road when this happens. The car has never stalled.

Any guesses as to why this only happens once in a while? Is this a sign of a major problem to come? Thanks for the help!

Post by **MadeInJapan** » 09 Aug 2007, 07:23

I suspect a vacuum leak....depending on weather and other conditions, a small tear in the vacuum hoses opens more....just a guess but worth investigating.

pmonk · Post by **pmonk** » 09 Aug 2007, 10:49

I think its a vacuum leak too. I had that and it was the plastic hose / tube between the air cleaner and engine. Easy to fix yourself if you buy the part. There were multiple cracks way down under it where you can't see them.

good luck

-p

icelandic · Post by **icelandic** » 09 Aug 2007, 13:41

The problem can be a dirty Idle control valve. It is that silver cylinder thing right next to the throtle body. With time It has a moving part inside the end where the two rubber hoses attach. Dirt accumulates in there and has to be cleaned up with carburator cleaner. Most times even WD-40 will work well.
It causes exactly the symptoms you describe, and it is occasional because
at that moment power electrical power is being derived to some other engine system, like AC compressor or rad cooling fan, causing a small fluctuation in voltage which makes the valve work slowly when it is activated.

danerrr808 · Post by **danerrr808** » 09 Aug 2007, 14:15

Thanks for the advice! I am going to try to clean the idle control valve first.

I actually own two 1998 S70 cars and I have noticed that the car with the idle problem has an idle control valve that vibrates a lot (almost as though it wants to blow right off the hoses). The other car has twice as many miles, but the idle control valve does not vibrate erractically, and this car has never shown signs of low RPMs as described.

I'll let you know if that fixes it. Thanks again!

danerrr808 · Post by **danerrr808** » 16 Aug 2007, 02:09

I did not get a chance to look at the Idle control valve or inspect the hoses. The spark plugs needed replacement, so I did that. Otherwise, the problem seems to have disappeared for now.