The car wouldn't start on Thursday arvo, one of the leads came off the back of the motor near the immobiliser. Reconnected, all good. While I was in there I cleaned the plug on top of the distributor, the plug to the ISC and TPS, oxygen sensor and the MAF sensor (I think, black box, far left of the engine bay near the filter).

All was well on Friday morning, but by the afternoon it was running badly, at idle the engine was running fairly low (400-500rpm) and even worse with the air con on. So I checked all the plugs again and cleaned them as necessary, but it didn't work, the engine is still running very badly (lowest was 50rpm) and I have no idea what to do. Symptoms are:

- Low RPM at idle
- With accelerator down, engine is fine (800rpm onward)
- With air con on, the revs bounce back as they should but not high enough
- Stronger smell of petrol in engine bay than usual (running rich)

Last time this happened it turned out to be the MAF sensor plug, it was dirty and wasn't making proper contact, cleaning did the trick. This time though the cleaning hasn't helped, even when I cleaned it with sand paper, as a last ditch attempt, it still didn't work.

I'm thinking it's the MAF sensor, but I haven't ruled out the ISC, the actual plugs that go to either or just the air filter itself. Could just replace all of them but I have no idea how much that will cost. I'm no expert though, so that's why i'm here now. Searched already (for "MAF sensor" and "rough idle") but it's come down to a new post, sorry everyone. lol

Hopefully we can shed some light on this.

Cheers
- Michael

Check your distributor out internally, ie. the rotor and contact points in the cap. If they're badly worn, it'll idle like crap. Also have a look at the leads for splits or anything like that; my previous car idled like a diesel with a dodgy ignition system.

Cheers, i'll check that first thing tomorrow morning. Anything else I should check while i'm in there?

Quick search of the forums again suggests a remote chance the Oxygen Sensor could be the culprit, I did clean those connectors out so it's a possibility. I'll go over it again just to be sure, heck, i'll try anything. :P

Is it missing, or just idling low?

It's idling low. Otherwise all 4 cylinders seem to be working as they should.

Check for vacuum leaks

Engine's running, when I started it this afternoon it idled about 600. Disconnected the O2 sensor and it climbed to about 900, brushed all the pins with metho again and it's sitting at 1100 but returning to about 900 after the initial "surge".

Still checking for leaks though to be sure, just stopped in to update the post.

EDIT: Spoke too soon :( It's running like crap again. Turned the AC on and it jumped back to 900. There's also a strange knocking noise near the front drivers side headlight but i'll investigate that later.

Gave the MAF sensor a few taps when the engine was running and the revs dropped, then bounced back. I'm beginning to think it's the MAF sensor and perhaps the plug.

Just read through this:

http://www.autocomputersupply.com/index.asp?PageAction=Custom&ID=8

Exactly the problem i'm having. Just for the hell of it I disconnected the ISC and started the engine and voila, perfect idle albeit around 1100rpm, but it's running. Looking back now it makes sense, the idle speeds have been fluctuating and surging for quite some time now.

So i'm guessing my ISC is stuffed, any way I can repair it temporarily (I hear adjusting a screw can help?) or what auto parts store will carry ISC's for a Mitsubishi Astron? I'd rather do the latter for piece of mind.

Will do another search of the forums now. (but up-to-date info is probably best, right?)

Most places will carry them.. bursons, repco, autopro etc etc...

Have the car idling, and turn the air con on.. and/or use power steering. If the revs drop or the car stalls, the ISC is knackered. Sometimes the pintle cap on the ISC gets stuck when alot of sludge accumulates on it. You can get away with removing it and cleaning it out with some carby cleaner.

See how ya go buddy.

It depends, when I turned the air con on earlier the revs dropped then went straight back up again, but a few seconds later they fell right back down again and didn't come back up. The revs seem to fluctuate up and down as well, and they have done for quite some time. A few times the car has stalled but not often, I can only recall 2 times when it's happened and both times the AC has been on.

The other remote possibility is the MAF although it seems to be working, air filter is pretty worn as well so i'll just swap the air filter out as well.

I'll probably head in there sometime this week and grab a new one. The plug itself looks somewhat worn as well, may solder a new one in when I get time.

Thanks :)

400 - 500 RPM is far to low, is this in DRIVE?


Up your idle switch, if it the cars struggling to stay on and you have very rough idle check the screw out! a simple phillips head screw driver and get it up to the 700-800 mark.

The rough idle will go down (at 400-500rpm in drive of course the car is going to run rough as its struggling to stay on)

Dont go over 800rpm as it chews more petrol

See how that goes, easier to try these things first before replacing parts then its still there!

It's 400-500rpm in Park or Neutral, in Drive it falls lower and really struggles to stay running, of course that's no issue once the car is running and accelerating.

when you said that the revs droped when you hit the maf sensor sound like a loose connection, try and get another one from the wreckers

A new MAF sensor is also on the cards as soon as I can get down to the wreckers next, probably when it's not so warm out.

I'm telling ya just adjust your idle switch - first and easy test

ISC is good to go, all running fine, revs are coming back up as they should. It did need a little work, cheers for pointing that out. :)

Once again though, a tap of the MAF or if you unplug & replug it, the car refuses to idle afterward. I think via process of elimination it's come down to the MAF sensor. The plug that runs into it is also in rough shape, so it may be a good idea to solder a new plug on while i'm at it. The dead giveaway is just how sensitive it is, if the plug shifts even slightly the revs fall dramatically, not to mention that the engine is running rich, so there is an interruption in the air supply.

Went to give it a start today, it started, and ran about 1100rpm in idle. No surprise, the engine was pretty much starved for air and burning just fuel which you could smell all around the car.

Anyway, that's not the point. However the real point is somewhat crazier.

I'm curious to know just what MAF sensors will fit this. I know the standard TR/TS sensors will fit it no problems, and i'm leaning toward a TS sensor, but keeping up my auto hacker mentality (not always a good thing), i'm curious to know what others may have done to their cars in this area. Eg. Sensors from a first or third gen, other Mitsubishi vehicles, etc.

I hope to have it back on the road this week, so far it looks like a full replacement of MAF, the MAF plug, O2 sensor and possibly the O2 sensor plug. Although the last two are precautionary maintenance.

Cheers :)

...interesting idea, keep me posted in a PM magna91... And on top of the comment about any 1st or 3rd gen MAF sensors fitting, what about any other mitsubishi models which may have a more "sportier" version, i.e. GTO etc etc...and would these fit?

Cheers,
Adz

Updated, it was pouring with rain last Monday so we just thought "stuff this, i'm not walking" and decided to take it anyway. Engine didn't run rough, but very rich. Took it out anyway and ended up doing this for about 3 days when the tank ran bone dry.

Went around, filled it up, rich smell gone. :confused:

I think there was a little too much injector cleaner in the system, considering I found quarter of a bottle left down from about 3 quarters. Fuel system cleared out and it's all good, as is the fuel economy. This doesn't explain the rough idle, since it was doing it before any injector cleaner was added, but it turns out if you plug in the MAF sensor that directly after plugging it in it'll run badly, but after it's been in there for a while (and possibly exposed to engine bay heat) it'll be fine.

I'll still be researching into MAF sensors and other parts anyway for the sake of documenting it really. Gives me something to do on the weekends.

Just nice to have the old workhorse back on the road and covered in dust once again. lol