My 2000 S40 has about 137K miles and generally ran well, but has the common long crank time before starting when cold. That is until I replaced the upper radiator hose - which coincided with a highly erratic idle, going as high as 6,000 RPM and now the car will not start when it is warm. The only When I do get it started it idles normally for about 3 minutes then climbs pretty quickly to the 5~6K range, the I shut it down fast. I have ordered the fuel pressure regulator to address the starting issue but the very high idle has me stumped and wonder why it started to happen right after I replaced the hose. The only other thing to mention is that 87 octane fuel was used a few days before the idle problem started, when I normally always use 93.
Any ideas???

 

The 87 isn't going to help you any, Turbo requests 91 or higher. That said, check for vacuum leaks all around, just take a spray bottle of water and mist over the hoses 1 at a time, try to track that down.

The radiator hose is also near the IAC , so you may have jostled something near there, unbolt your IAC, clean that (fill it with carb cleaner and let it soak some) and the electrical connector for it. while you're in there, you may as well also clean the throttle body/plate. Check the integrity of the IAC gasket as well, it's a cheap paper gasket, and if that blows out you're gonna get a pretty sizable vacuum leak right on your intake.

Get some 104 octane booster or similar to try to offset the cheap gas as well. The car REALLY doesn't like to run with anything less than 91, in fact, the manual says pretty specifically not to run it with 87 or 89.

 

I realized that I was in over my head so took it to a good local shop. So far they are going to replace the temp sensor and have cleaned the throttle body and IAC. Also going to replace one coil pack and new wires and plugs. Those items were not the root cause of the 6000prm idle but were needed anyway. Hopefully that will do it - will find out later today.

 

What did you find out with this problem?