I just bought a 1994 Dodge Colt ES 1.8l with a 5 speed. I like it so far. Mechanically everything seems sound, while a few other things weren't maintained as well (trunk liner/carpet gone, glovebox broken).

I do have one problem, however. With the aircon off, the engine idles pretty low, around 500rpm. I have killed the engine a few times because when the revs are so low and you give it gas, it sputters a little before revving up. This doesn't happen with the aircon on, because the idle goes up to 7-800rpm, where it should be.

I also have a check engine light on. I don't have a voltmeter, so I can't diagnose it quite yet. I wonder if the two are related?

Any help would obviously be appreciated.

They can be related , Well i have cousins that have older Mirage Asti's etc similar to yurs i am guessing in most aspects , and they have had the cars since brand new and have had same issues , theirs wore down frum regular wear , the glove box , his latch broke also , his trunk leaked after 11 years. Now we have also used a multimeter to get codes , i find the multimeter alot easier to retreive codes. It could be one of 2 things. The TPS sensor or teh MAF meter. BUt it could very well be the TPS . These are teh 2 things yu want to check for.

If I'm reading my voltmeter correctly, it shows 14DCV, which is 14, which is the TPS. Anybody got a cheap TPS?

Many Mitsubishi models gave that same TPS , get it off of like , a 1990-1995 3000GT , Diamante , 1990-1994 Eclipse (not 1.8 engine) 1990-1993 Mitsubishi Galant , (1990-1995 Mitsubishi DOCH engines) 1994-1995 Mitsubishi Galant , get one off these models for temp and try it out , its should solve yur issue. , Make sure yu adjust it on the white marks that should be on the TPS

Have you adjusted the tps. If not you might want to adjust it so that the tps position is correctly on idle. The tps will make a clicking noise when you turn it to the right position.
Or what you can do is just increase the idle, turn the idle speed screw to get a higher idle. or you might just want to increase the gap of the throttle plate, there is also a screw for this. good luck

He has a faulty TPS

Oh I see... hahaha, then you might want to change the tps to solve your low idle problem. good luck..

Anybody got a picture of the TPS?

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I took the TPS off and readjusted it, and the idle problem is gone. But I haven't reset the code to see if it pops back up.

Did yu adjust it , more so than teh factory adjustment? Pick up the adjustment frum where the white marks are? It may cure the problem for a while , but also make the vehicle burn a little richer in fuel than if at the factory setting . Thing is it most likely has a dead spot in near the rest position of the TPS. Adjusting the TPS over the factory settings will temporarily correct that .