Hot idle speed oscillating

[Guv Bob]

My 1990 Mitsubishi Eclipse (DSM 1G 2L non-turbo) is starts and idles cold 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.

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.

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

 

[Jamie]

Guv Bob wrote:

My 1990 Mitsubishi Eclipse (DSM 1G 2L non-turbo) is starts and idles cold 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.

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.

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

O2 Sensor?

Jamie

 

[Guv Bob]

"Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote in message news:lQvyr.54484$ax3.31338@newsfe05.iad...

Guv Bob wrote:

My 1990 Mitsubishi Eclipse (DSM 1G 2L non-turbo) is starts and idles cold 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.

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.

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

O2 Sensor?

Jamie

Thanks Jamie. Checked it out today and was OK. Also getting good signal from computer to sensor.

 

[Jamie]

Guv Bob wrote:

"Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote in message news:lQvyr.54484$ax3.31338@newsfe05.iad...

Guv Bob wrote:


My 1990 Mitsubishi Eclipse (DSM 1G 2L non-turbo) is starts and idles cold 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.

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.

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


O2 Sensor?

Jamie


Thanks Jamie. Checked it out today and was OK. Also getting good signal from computer to sensor.


Some one made a suggestion of a vacuum leak.. If you remove the load

from the engine, it cold have problems at idle.

You may want to check your EGR valve if you have a vacuum type servo
on it.

I wonder if you have problems with your air ducts? In some vehicles,
the defrost for your windshield behaves differently if you are sitting
in part verses rolling down the road. Is it possible your vacuum servos
for your air duct system has a leak? I know in my new jeep it changes
behavior if I am sitting there in park verses drive. I think it is to
keep the air from blowing on your face? When you have the engine
loaded, you most likely wont feel this. You may even have a vacuum
switch on your shifter or from the ECM.

Jamie

 

[Guv Bob]

Thanks Jamie, will check it out.

"Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote in message news:%GQyr.1852$8l2.1216@newsfe14.iad...

Guv Bob wrote:

"Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote in message news:lQvyr.54484$ax3.31338@newsfe05.iad...

Guv Bob wrote:


My 1990 Mitsubishi Eclipse (DSM 1G 2L non-turbo) is starts and idles cold 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.

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.

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


O2 Sensor?

Jamie


Thanks Jamie. Checked it out today and was OK. Also getting good signal from computer to sensor.


Some one made a suggestion of a vacuum leak.. If you remove the load
from the engine, it cold have problems at idle.

You may want to check your EGR valve if you have a vacuum type servo
on it.

I wonder if you have problems with your air ducts? In some vehicles,
the defrost for your windshield behaves differently if you are sitting
in part verses rolling down the road. Is it possible your vacuum servos
for your air duct system has a leak? I know in my new jeep it changes
behavior if I am sitting there in park verses drive. I think it is to
keep the air from blowing on your face? When you have the engine
loaded, you most likely wont feel this. You may even have a vacuum
switch on your shifter or from the ECM.

Jamie

 

El lunes, 4 de junio de 2012 18:43:02 UTC-4:30, Guv Bob escribió:

Thanks Jamie, will check it out.

"Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote in message news:%GQyr.1852$8l2.1216@newsfe14.iad...
Guv Bob wrote:

"Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote in message news:lQvyr.54484$ax3.31338@newsfe05.iad...

Guv Bob wrote:


My 1990 Mitsubishi Eclipse (DSM 1G 2L non-turbo) is starts and idles cold 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.

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.

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


O2 Sensor?

Jamie


Thanks Jamie. Checked it out today and was OK. Also getting good signal from computer to sensor.


Some one made a suggestion of a vacuum leak.. If you remove the load
from the engine, it cold have problems at idle.

You may want to check your EGR valve if you have a vacuum type servo
on it.

I wonder if you have problems with your air ducts? In some vehicles,
the defrost for your windshield behaves differently if you are sitting
in part verses rolling down the road. Is it possible your vacuum servos
for your air duct system has a leak? I know in my new jeep it changes
behavior if I am sitting there in park verses drive. I think it is to
keep the air from blowing on your face? When you have the engine
loaded, you most likely wont feel this. You may even have a vacuum
switch on your shifter or from the ECM.

Jamie

Couldn't it be the gearbox comparator sending wrong/wild signals to the computer? it's kind of strange that moving it from parking to neutral would cause this change, the gearbox entry shouldn't add such strain on the engine as to cause this...

 

[Guv Bob]

<lars.gold@gmail.com> wrote in message news:d636ec04-c90c-4cc1-8eab-d382860e415c@googlegroups.com...


El lunes, 4 de junio de 2012 18:43:02 UTC-4:30, Guv Bob escribió:

Thanks Jamie, will check it out.

"Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote in message news:%GQyr.1852$8l2.1216@newsfe14.iad...
Guv Bob wrote:

"Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote in message news:lQvyr.54484$ax3.31338@newsfe05.iad...

Guv Bob wrote:


My 1990 Mitsubishi Eclipse (DSM 1G 2L non-turbo) is starts and idles cold 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.

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.

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


O2 Sensor?

Jamie


Thanks Jamie. Checked it out today and was OK. Also getting good signal from computer to sensor.


Some one made a suggestion of a vacuum leak.. If you remove the load
from the engine, it cold have problems at idle.

You may want to check your EGR valve if you have a vacuum type servo
on it.

I wonder if you have problems with your air ducts? In some vehicles,
the defrost for your windshield behaves differently if you are sitting
in part verses rolling down the road. Is it possible your vacuum servos
for your air duct system has a leak? I know in my new jeep it changes
behavior if I am sitting there in park verses drive. I think it is to
keep the air from blowing on your face? When you have the engine
loaded, you most likely wont feel this. You may even have a vacuum
switch on your shifter or from the ECM.

Jamie

Couldn't it be the gearbox comparator sending wrong/wild signals to the computer? it's kind of strange that moving it from parking to neutral would cause this change, the gearbox entry shouldn't add such strain on the engine as to cause this...

==
Howdy Lars.

A lot of time and work were between posts. It turned out all the sensors were fine. Went over it one by one, checking sensor signals, ECU signals and connections.

Troubles were..... 2 burnt capacitors in the ECU (not a big deal - just followed my nose. LOL!!) Turns out that that brand of cap were later discarded by Mitsubishi.

Wrapped some worn insulation on a cable that was shorting the O2 sensor signal intermittently. Bad connections all over - throttle position sensor connector was loose.

At that point I got the car running fine, except when the engine was up to temp, it oscillated when in not in gear. In gear it was fine. I suspected a temp sensor at first, but it was simpler than that. Evidently when I cleaned the idle speed stepper motor, it was not reset properly and the ECU could not move it far enough during idle. This procedure did the trick....

It shows how to isolate the idle stepper from ECU, reset it and then set the idle. Much easier to follow and better illustrations than most shop manuals.... http://www.vfaq.com/mods/BISS-1G.html

Hopefully this will be my last fix-it posting on this car for awhile!

Thanks to everyone who posted and pointed me in the right direction!!

Bob