Hey all, having my 91 740 idle anytime after I start the engine it tends to go to ~500 rpm and sometimes ~125 rpm. After I drive somewhere in the city or anywhere else it idles normally after i put in park. Any ideas?

 

Sure. Have you pulled the codes? Three things come to mind. If the TPS is not adjusted correctly, the ecu does not know the engine is idling and will not control the IAC. Besides a bad or mis adjusted TPS, the throttle blade in the throttle body could be so nasty that it doesn't close completely. Second, there might be issues w/ the IAC itself. It could be unplugged, a hose off, failed or dirty inside. Third, ALL turbo cars are particularly hard on vacuum hoses. This is for a couple of reasons. The additional heat from the turbo is hard on stock rubber hoses. In addition, unlike n/a cars, the vac hoses hold positive pressure under boost. Your car is 22 years old...if it hasn't been done...ALL rubber hoses need to be replaced. From experience, I will tell you I have spent half a day tracking down leaks in vain. So, my advice is to consider it maintenance and swap them all out. If you have the money, use silicone hose as it is much more resistant to heat. I swap out the brake booster hose as well and swap out the IAC hoses with genuine Volvo when still available.
Turbo cars are a lot of fun, but at their current age, they need a bit of neglected periodic maintenance.

 

I think it would most likely be the hoses. They are still the same ones that came on the car when my parents bought it in '91. I already replaced some of the fuel lines becase of the dry rot and the fact that I could not keep gas in the tank for more than 150 miles. I will replace the hoses once i get the money (just got a job) and when i have the time.

 

Now, all I need to do is figure out where the hoses are located. I'm not really that smart when it comes to vacumm hoses. All I have done on the care mostly consists of replacing fuel lines.

 

all the skinny hoses that start or end at the intake manifold are vacuum hoses.

 

Thanks all.