Odd Idling Problem. 93 Civic SI

I just bought a 93 Civic SI Hatchback. Everything looked and ran fine. I drove it 3 times over the course of 2 different days. After I got it home, it started doing something odd.

It started ideling wierdly. It will go up and down between about .5k and 1.5k RPM. One time, it idled so low that the car stalled out, and didn't want to start back up. It ran perfectly fine when I test drove it, but now it's acting up.

Any ideas?

Are there any other symtoms like smell of gas, smoke, overheating, oil leak or burning smell? Feel free to comment on other things you think are out of place other than what I've mentioned.

Sometimes the smell of exhaust, or possible something burning. it's nto always there though.

Are you still having problems starting up? I would start with your basics for the moment. Check your oil, and coolant, and look for leaks. I'm not sure but there may be a problem with your fuel system. It sounds like the engine isn't getting enough gas, so the ecu is sending more, that would cause it to surge, and then when it get's too high it's cutting out but can't maintain enough steady pressure to get a smooth idle. That's a real stab in the dark though. It would be worth looking into but there are other things that can cause problems like this.

I checked it this morning. When it started it idled at 2.4k rpm then after about 10 seconds went down to 2.1. Shortly after that it started going up and down between 1.5 and 2.

Coolant and oil looked fine, and there weren't any noticable leaks.

If it is the fuel system, what should I do to check it? Or would it be better to take it to a shop?

Thank you.

Whether or not you should take it to a shop is really dependant on how comfortable you are doing the work. I think that an oil change is easy and that most people could do that at home but there are others who aren't comfortable enough to attempt it.

You may need a fuel pressure gauge to check your fuel system. If you buy a gauge, you may need to buy a fitting to attach it to the fuel system. Your fuel pressure needs to be between 40 - 47 PSI with the vaccum hose detached. If you need a service manual to help, click here (http://www.automotiveforums.com/vbulletin/showthread.php?t=581305).

Once again, I'm not solidly sure that the problem is the fuel system. Is your check engine light on?

Yes, it is, but the O2 sensor is also unplugged. The last owner put an aftermarket air intake on it and unplugged the sensor. I couldn't find it on the harness, so I didn't plug it back in.

Ok, I have some new info. I drove the car a couple short distances today to see how it would act. It's still bounces between 1.5 and 2 idling, but as I start to drive it, it stops doing that. It'll idle stable at about 1.5 or so at first, but after driving it for a few minutes it'll idle pretty stable at about .2 . When driving with the gas at a constant pressure it'll stay stable without bouncing. Is about .2 too low for idle? I've driven a stick shift for years, but that Civic (90 DX hatchback) didn't have a tach.

Does that help any?

EDIT

Ok, I went to get back in it and take off again. It started up, stalled out, and now it doesn't want to start again. Sounds like it's trying to turn over. I guess I'll have to wait until tomorrow. I'll have a shop look at it to figure out the problem. Unless someone has a better idea od what might be wrong. I don't know.

O2 sensor needs to be put back. That's my guess.
Strange that he would remove that sensor when changing out an air intake. O2 is on the exhaust.

Where is the plug located for the sensor? Be as exact as possible.

Where is the plug located for the sensor? Be as exact as possible.


Located within the exhaust manifold. Is that good enough?

How about a picture
http://media.honda.co.uk/car/owner/media/manuals/CivicManual/pdf/9-4.pdf

I think I'll just have a shop check it out and go from there. If possible do the work myself. But first thing's first.