Hot idle speed oscillating

On Fri, 1 Jun 2012 22:33:04 -0700, "Guv Bob"


and runs fine warmed up.  When warm and I put it in neutral (AT) the idle
oscillates between 1800 and 2200 with about 1/2 second cycle time.

same problem.  Checked all the connections and vacuum - all OK.  

still oscillating.   Cleaned Idle air motor, checked voltages and resistance for
all senosors and also voltages coming from the computer, and all OK.

this?

disconnect the idle speed control and see if it levels out.  If so it
is most likely idle speed control related.

If not something else is changing the idle speed and the system is
chasing it's tail. I'd suspect an air leak in the intake .

You don't by chance have the AC or defrost turned on??????

(AT) the idle oscillates between 1800 and 2200 with about 1/2 second =
cycle time.

OK. =20

voltages and resistance for all senosors and also voltages coming from =
the computer, and all OK.

Thanks a lot, Clare.  Will check it out tomorrow and post an update.  No =
AC or defrost on.

Still looking for the problem.

Probably not related, but any idea what this part is?  It has 4 leads =
that feed into the wiring harness and can't trace it any farther.  Looks =
like a solenoid but can't find it in Haynes or other manuals I have.
Not sure if the first photo took, so uploaded it again...

http://imageshack.us/photo/my-images/833/dsm1g20.jpg/
http://img593.imageshack.us/img593/8655/dsm1g20.jpg

Sorry for posting in the Ford group, but it's the best auto newsgroup =
I've found - alt.autos, and mitsubishi are dead.  When I post in =
electronics newsgroups I get "post in an auto group..."

Thanks again.

Bob



(AT) the idle oscillates between 1800 and 2200 with about 1/2 second =
cycle time.

OK. =20

voltages and resistance for all senosors and also voltages coming from =
the computer, and all OK.

Welll... 4 leads? And it looks like a relay? Then I'd say its a
relay.
Test it..
You could ohm it out. You should get some sort of resistance across two
of the pins. Maybe about 100 Ohms. That would be the coil.
And the other two should read either open or closed, depending on what
it was supposed to do. Then put 12V to the coil pins and the thing
should click and if the other two pins read open before then now they
should read about 0 Ohms. If you get no change or a high resistance
after the relay switches then its no good.

Fred


Guv Bob wrote:

feed into the wiring harness and can't trace it any farther.  Looks like a
solenoid but can't find it in Haynes or other manuals I have.

found - alt.autos, and mitsubishi are dead.  When I post in electronics
newsgroups I get "post in an auto group..."

fine, and runs fine warmed up.  When warm and I put it in neutral (AT) the idle
oscillates between 1800 and 2200 with about 1/2 second cycle time.

and same problem.  Checked all the connections and vacuum - all OK.

still oscillating.   Cleaned Idle air motor, checked voltages and resistance for
all senosors and also voltages coming from the computer, and all OK.

troubleshooting this?

On Fri, 1 Jun 2012 22:33:04 -0700, "Guv Bob"


and runs fine warmed up.  When warm and I put it in neutral (AT) the idle
oscillates between 1800 and 2200 with about 1/2 second cycle time.

same problem.  Checked all the connections and vacuum - all OK.  

still oscillating.   Cleaned Idle air motor, checked voltages and resistance for
all senosors and also voltages coming from the computer, and all OK.

this?

When my 88 Ford did that it was caused by a faulty Idle Air Bypass
Valve, which is used to control the idle speed.  It's like a
mini-throttle body just for idle speed control.

Doesn't the Mitsubishi engine use an idle pintle?  Looks like an acorn on a
stick.  A solonoid pulses it to allow air to bypass the throttle body
butterfly valve when it is fully closed.  They say NEVER take that thing
apart, but I've done it to my Intrepid.  Just be VERY careful about loosing
parts.  I cleaned mine up with carb and brake cleaner (don't let the brake
cleaner get on anything but the pure metal parts) and be careful when you
reassemble it.  Any mistakes and your engine could race at wide open
throttle when you first start it back up.

a lot of people tried disassembly and cleaning of the ford IABV.
Results were hit and miss.  I tried cleaning mine a couple times and
it made it worse.  Gave up and just bought a new one.  There was also
a very specific procedure for adjusting the base idle speed and screw
position.  Sometimes following that adjustment procedure helped and
sometimes it didn't.  There were also several un-official adjustment
methods also which sometimes helped and sometimes didn't.  Some
vehicles just seen like they have ghosts in the idle circuit.

Sorry for not posting back sooner.   After a dozen fixes and half dozen =
weekends the engine runs like new again.  Hardly any $$ spent - mostly =
isolating bad elec connections and cleaning.  Did replace 2 capacitors =
on the ECU that had burned - biggest problem.

Like you suggested, the last problem with oscillating idle was =
definitely related to the ISBV.  This fellow's reply was right on the =
money.....

----- Original Message -----=20

From: jurb6006@gmail.com=20
Newsgroups: sci.electronics.repair
Sent: Wednesday, August 01, 2012 9:11 PM
Subject: Re: Hot idle speed oscillating


.... 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 goes 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. This 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 cannot usually readjust the IACS to compensate.=20

But if you see a bunch of black shit in there of course clean it =
somehow. Throttle 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 the hole. (same shit happened to carbs that were run a =
long time without an air 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. On an American car it is a tang and you just bend it, on other =
cars you might have to shim it, or even find the actual adjustment. This =
will keep the throttle from closing too much. You MAY have to do =
something about the TPS if it is not adjustable.=20

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

So if you fuck with the idle position of the throttle, do it only as =
much as you need. (both of these solutions are against "code" but legal =
if it pases 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.

Thanks for posting the end of the story.



On Mon, 13 Aug 2012 10:49:10 -0700, "Guv Bob"


weekends the engine runs like new again.  Hardly any $$ spent - mostly isolating
bad elec connections and cleaning.  Did replace 2 capacitors on the ECU that had
burned - biggest problem.

related to the ISBV.  This fellow's reply was right on the money.....

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.

goes down. This skews the actual IACS from the true reading, indicating to the
computer the amount of IA is higher than it is.

IAC postiton to where it does not give enough IA. Then the computer goes 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. This sustains the
oscillation. (hunting)

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 cannot
usually readjust the IACS to compensate.

Throttle 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 the
hole. (same shit happened to carbs that were run a long time without an air
filter, but the solutions were different)

tang on the throttle linkage right there on GMs, it may be hard to find. On an
American car it is a tang and you just bend it, on other cars you might have to
shim it, or even find the actual adjustment. This will keep the throttle from
closing too much. You MAY have to do something about the TPS if it is not
adjustable.

IAC pintle might get thrown down into the seat so hard the it will get stuck
there, and then you will have a stalling ocndition and a constant check engine
light.

you need. (both of these solutions are against "code" but legal if it pases
emissions, and it should)

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 ?

have changed for the IAC. The parameters of the intake cuircuit.