What causes idle speed to be low?

Have you checked the engine codes yet? Buy a code reader or go to a place like AutoZone where they will read them for you for free. They have a wealth of information. Get both the active codes and the pending codes.

They didn't have this style when I bought mine, but it seems like it would be economical,

Both of them schould work with just about every car sold for the last few years, and the expensive one will probably be updated for future cars for several more years.

These don't do transmission codes afaik. Well one comment says the expensive one does "OBD scanners plug into your car’s OBD-II port to read and clear diagnostic trouble codes (DTCs), identifying issues like engine misfires and transmission problems.". Iow, it includes transmissions but the comment is from a girl and what do they know? No, I'd doubt it no matter who said it.

I'll have to read this later.

Plus there are the standard, original style with a built in screen and button contols.

Search google for Read Transmission Codes and one hit is in Amazon "transmission diagnostic tool" but don't assume that every hit will actually read transmission codes. Amazon will mix in things that don't meet the search criteria with things that do meet them!! It does this all the time.

The ones that do read xmission codes seem pretty expensive. (Long story about the time I had a transmission problem for a while, deleted.)

And then there are airbag codes. Cheap readers don't read them either, but you don't have to read those. Just wait until there is a collision and see if the bag opens. I suppose they turn on the Check engine light, or is there a check bag light?

Ken Blake wrote: > I have a Mitsubishi Lancer 2003 which has low idle speed. > So low that it stalls unless I keep the gas on the peddle. > What causes that? > And more important, how can I adjust it?

It could be due to a bad or clogged sensor: MAF, TPS, IAC, IAT, MAT, O2. My guess is TPS or IAC.

You can clean the MAF, IAT, and possibly the IAC. You can check the ohms of most of them. Most of the sensors run at 5 volts due to using TTL circuits. You can check voltages of many of them at KOEO (key on, engine off). The O2 should be between 0.1 and 1.0 volts depending on temp.

This shows some data... don't know where to get the manual.

Most cars I have driven had a specific telltale light for airbags, and another telltale for ABS/ESC stuff.

You're thinking backwards. Think about what happens when you're at idle. Something needs to happen to make the mixture more rich, and that could be done in all kinds of different ways. Some cars have an extra injector just for idle, some have software in the ECU that runs the normal injectors more rich, some have a gadget in the carb that is activated by engine vacuum.

I have never worked on a Lancer, but less than a minute with Alldata shows me that you have an idle control valve. Check it and make sure it is functioning properly. Is it getting a control signal from the computer to open and close? The meter will tell you. Is it actually opening and closing? Your finger blocking the entrance will tell you.

Plenty of other things can cause the mixture to get messed up at idle and that includes vacuum leaks, so if the valve is operating properly checking out the vacuum lines is your next step.

If you use a crappy scanner that just gives you codes, you will see a bunch of codes saying the mixture is wrong, but you already know that. You don't need the scanner to tell you.

If you use a proper mechanic's scanner you can see all the inputs coming into the ECU, which includes the mass air flow sensor, and you can see if those inputs are good and whether or not the ECU is opening and closing the valve properly. This is useful information but the most important information comes from your eyes and ears.

You do not, you fix it.

Alldata will get you a manual if you don't have one, but for this car even a Haynes will probably tell you what you want.

--scott

A total crock of s*it Scott . Idle mix is NOT enriched , if anything it's leaned out . I strongly suspect it's either an IAC or the MAF sensor that's malfunctioning - IAC is most likely , and can USUALLY be cleared up with being cleaned with carb spray . The best thing for him to do is have one of the local parts stores run an OBDC2 scan . Just about every parts store does this for free . Makes sales for them and saves the customer money by not just throwing parts at an undiagnosed problem .

Modern cars are too complicated. The idle used to be controlled by a screw that stopped the throttle from closing completely.

Yeah, I recall President Eisenhower mentioning how functional that arrangement was during a Rose Garden press conference.

That complication has brought us more powerful and clean burning IC engines too . There was a sweet spot in the late 90's and up to about

Odd, that's what the IAC does in a TBI/PFI engine - allows air to bypass the throttle body.

Anyway, in order to better control emissions, the last of the carbs became too complicated. TBI/PFI simplified fuel delivery as well as making it more accurate and, at the same time, providing better atomisation/vapourisation. Carbs, dead and buried.