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Doug, ASE Certified Technician
Category: Mitsubishi
Satisfied Customers: 8609
Experience:  Mitsubishi employed and Factory trained ASE certified technician
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We have a 1996 mitsubishi mirage 1.5 since new. It started

Customer Question

We have a 1996 mitsubishi mirage 1.5 since new. It started idling irratically and would start hard or not at all, with a strong gas smell. The idle air control had a broken gear inside. The control was replaced with a new one. It idles much better now but occasionally will not start with the gas smell again present. A new code now is shown, p0505, which reads "idle speed control malfunction". Mitsubishi could not or would not say what this means. "Bring it in, but if it is running OK when we check it,we might not be able to find the problem." Any ideas on what to check? I have an ohm meter and know how to use, watch out! Thanks, Gene
Submitted: 1 year ago.
Category: Mitsubishi
Expert:  Doug replied 1 year ago.


The P0505 simply means that the system is trying to reach its proper idle for the temperature but can not reach it after maxing out the IAC. If you are certain the IAC is good (we do have hit or miss issues with aftermarket ones unfortunately), then you would expect this to be the result of an intake leak, someone having fiddled with the set screws on the throttle body, or an ecu issue (somewhat common in this capacity).

This is unlikely to be related to your fuel odor, unless you are really over fueling to the point that it is causing the idle to stutter.

With that being said, can you test your fuel pressure? Specifically cranking pressure, running pressure, running pressure with vacuum line detached from regulator, and pressure after key-off for 2-3 minutes?

Customer: replied 1 year ago.
Since it has started and run well on average of 3 times to 1, at different temps, What else might I look at? I did in fact "fiddle with the idle screw " on the throttle body in the past, of course I did! Yesterday when it wouldn't start and smelled gassy, I disconnected the connector to the TPS, held the throttle open, my wife cranked it and it started and raced for a second until the throttle was released.Hooked up the connector and it ran fine.I will get items to test fuel pressure if you think it's a critical test.Thanks, Gene
Expert:  Doug replied 1 year ago.

Thanks Gene.

If you have adjusted the idle stops.... I would certainly fix those first. The dead stop can be set with a multi meter... unplug the TPS and find the 5V wire, then plug it back in and back probe that wire. Then adjust the stop until it shows about 600-700mV. This is sort of a backwards way of doing it, but will get the job done (it is actually done for setting the TPS position, but if it is in position then adjusting the dead stop to the same point would get the same thing accomplished).
The SAS or bypass screw on the top of the throttle body.... you need a scan tool to set it properly. You can turn the AC off and adjust it to around 700 RPM (warmed up) and it will be close enough for our needs, but to get it actually dialed in exact a scan tool is needed to set the IAC to its SAS set position, then adjusted.

As for your issue.... when you have a strong fuel odor it is exactly what you expect 95% of the time... theres too much fuel there. This can be due to low fuel pressure (as the pressure lowers it no longer atomizes properly and causes it to run rich) from either a weak pump, a blocked fuel filter, or a failing fuel pressure regulator. Additionally it can be had from leaky injectors too.... and this is a pretty worthy concern at this age for the vehicle. If you have an injector that is leaking slightly, for example left to sit over night and it decides to bleed down, this will cause an awful fuel odor on startup and can even cause difficulty starting depending on the severity. This is one of the areas where a fuel pressure test would be handy, as you could monitor the pressure after key off and see how quickly it bleeds down. It should hold almost all of its pressure for hours and hours. If you see it lose for example 10 psi in a couple minutes, you have a problem.

Apart from the fuel pressure, going over your ignition items would be a good idea making sure the plugs are in very good condition else replace them (they are usually recommended every 15k) and check the wire conditions for age as well. If you have weak spark you will inherit a rich condition on startup as they try to get going, and again you end up with fuel odor.