Hot idle speed oscillating

Have you looked for an air leak (using carb cleaner or blowtorch gas)?

I suggest you try a car repair group though, this isn't one.

Gareth.

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Thanks Gareth. Yes, checked already. Vacuum, electrical connections, = mechanical etc., all seem to be OK. It's definitely in the = electronics. Car groups are good but gotten better help with auto = electronics from these elec groups.

Cars aren't really my forte. Is the engine management light on?

Try the youtube route if you haven't already, particularly how to find vacuum leaks, even though you're sure you don't have one. :)

These ODB readers are really cheap now if you don't already have one:

Sorry if you've done all this already, but you haven't given a lot of data!

Good luck.

Gareth.

Oops,

meant to include this one too:

Gareth.

It's a 22 year old rice burner, doesn't the junk yards still give $50 for them?

I don't know if this applies, but the description of the symptoms is nearly identical to a problem a freind of mine had with a same vintage (1990) pontiac.

After trying everything you listed you've done, including swapping out the computer/brain box, something lead him to the magnet sensor thing on the fly wheel.

It wasn't the sensor itself (that was replaced) but the magnet glued to the flywheel. Turned out it cracked, causing the pulse it sent to the computer was distorted or too narrow to get an accurate reading.

While cold, the reading is ignored, along with some other sensor readings until the engine came to operating temp, once it got into the picture, the idle speed went up and varied.

Keep in mind the pulse was still being sent, but apparently deformed and however it was translated into a reading, was off enough for the computer to think it was idling too slow.

-bruce snipped-for-privacy@ripco.com

Thanks, Gareth!

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Any idea what this part is? Has 4 leads, and looks like a solenoid but = can't find it in Haynes or other manuals I have.

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Thanks,

Bob

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find it in Haynes or other manuals I have.

Fuel pump relay?

it is a relay, that's is for sure. 2 wires are the coil and the other two are the contacts. and it looks like you have burnt leg.

Jamie

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, mechanical etc., all seem to be OK. =A0 It's definitely in the electronic= s. =A0Car groups are good =A0but gotten better help with auto electronics f= rom these elec groups.

Try to find a Mitsubishi online forum. If I have trouble with my Golf, I go to vwvortex.com . Ninety percent of the time, someone else has had my problem and solved it, with a step-by-step DIY posted, along with pics.

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mechanical etc., all seem to be OK. It's definitely in the electronics. = Car groups are good but gotten better help with auto electronics from = these elec groups.

Try to find a Mitsubishi online forum. If I have trouble with my Golf, I go to vwvortex.com . Ninety percent of the time, someone else has had my problem and solved it, with a step-by-step DIY posted, along with pics.

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Yes, I've been searching a lot but had so many things out of adjustment = it's taken many weekends. This is a great newsgroup because most auto = repair sites are mostly for mechanical fixes. Electronics folks can = pretty much solve any type of electronics problem regardless of what the = application is. This newsgroup and rec.craft.metalworking are always = good for helpful folks. Any group that has "computer" in the name is = worthless as far as anything inside the cover goes.

Bob

Finally!! It's idling and running stable and like new again. Here's = an excellent procedure on how to isolate the idle speed stepper motor = from the ECU, reset it and then set the idle. Much easier to follow and = better illustrations than most shop manuals.... =

It's amazing how "easy" it was now that it's all done. LOL!!! Edison = was right about it being 90% perspiration.

Bob

MAS was the first guess -- so I put a rebuilt mass airflow sensor assy = in and same problem. Checked all the connections and vacuum - all OK. =20

Also took the throttle assy apart and cleaned all - helped the running = but still oscillating. Cleaned Idle air motor, checked voltages and = resistance for all sensors and also voltages coming from the computer, = and all OK.

About out of ideas -- anyone have some thoughts on how to start = troubleshooting this?

Thanks in advance.

Bob

Hold on, f*ck all this. If you can't find it in the codes, it can only be a= few things.=20

Dig up, the first check is to keep it running until it does it. If it won't= do it out of gear get some really good wheel chocks. When the idle hits a = high point, unplug the IAC (or it's equivalent). If the hunting stops there= are one of two things possible, but one solution might do it.=20

More than likely the IA path is partly clogged, especially where the pintle= goes down. This skews the actual IACS from the true reading, indicating to= the computer the amount of IA is higher than it is.=20

The IAC responds based on presets in the computer so therefore it will cut = the IAC postiton to where it does not give enough IA. Then the computer goe= s into "stumble" mode, thinking (rightly) that it is about to stall because= the idle speed has dropped too much. It will then open up the IAC to allow= more air. The computer will always look for the lowest idle attainable. Th= is sustains the oscillation. (hunting)

Now, if you rebuild the throttle body, it will be cleaned and hopefully be = alright but then there is a possibility that the seat for the pintle valve = has been eroded too much. You usually cannot machine this out because you c= annot usually readjust the IACS to compensate.=20

But if you see a bunch of black shit in there of course clean it somehow. T= hrottle bodies really never need much of a rebuild other than that, if it's= worn you might have to machione down a bore so the IAC drops lower into th= e hole. (same shit happened to carbs that were run a long time without an a= ir filter, but the solutions were different)

However, if it is actually worn like that there is a workaround. There is a= tang on the throttle linkage right there on GMs, it may be hard to find. O= n an American car it is a tang and you just bend it, on other cars you migh= t have to shim it, or even find the actual adjustment. This will keep the t= hrottle from closing too much. You MAY have to do something about the TPS i= f it is not adjustable.=20

The drawback to not replacing the throttle body for this problem is that th= e IAC pintle might get thrown down into the seat so hard the it will get st= uck there, and then you will have a stalling ocndition and a constant check= engine light.=20

So if you f*ck with the idle position of the throttle, do it only as much a= s you need. (both of these solutions are against "code" but legal if it pas= es emissions, and it should)

If you don't do something though, it will eventually start stalling at red = lights. Alot of people told me "well it was doing that idle thing for years= and now it stalls". What, did you think it was going to fix itself ?=20

But it is not sensors. It is probably not the IAC itself, it is that things= have changed for the IAC. The parameters of the intake cuircuit.