(solved)Fault: idle rpm jitters between ~1k-2k

[Ian Rogers]

Not faulty!!! The oxygen sensor is doing its job!! Because it can only move so far it cannot compensate that's why its hunting... If you pump the brake you are taking air from the system.. so there is too much air and the lambda sensor is reaching its max...

 

[fezder]

Not faulty!!! The oxygen sensor is doing its job!! Because it can only move so far it cannot compensate that's why its hunting... If you pump the brake you are taking air from the system.. so there is too much air and the lambda sensor is reaching its max...

oops, i misread you post, sorry

the fact is, i'm pretty green with automotive stuff, so you guys are great help, no matter the outcome!

 

[cowboybob]

wohoo, that is one the few parts that haven't been changed yet ...
is it lampda-sensor btw?

Probably.

With NO brake application (as evidenced by your videos), Note

Unusual Lurching Or Hesitation

• An early warning signal of Lambda sensor failure in the form of an uneven idle can be noticed by a driver who feels the vehicle wanting to surge ahead when at a red light or stop sign. Or, conversely, when it is time to go, the driver feels the vehicle hesitating after the accelerator is applied.

From this site: https://www.ehow.com/list_6005864_symptoms-faulty-lambda-sensor.html

 

[fezder]

took off IAC, same thing goes on, no difference with, or without it. started engine without it

 

[cowboybob]

This also:

"Thanks for the video. My 95 Dodge Ram was doing exactly what you described, and when I removed the electrical from the IAC, cleaned the contacts, and put it back, she runs perfectly now. Your video saved me a lot of time and money. Cheers."

From:

Cheaper, easier than an Oxygen Sensor replacement.

 

[cowboybob]

took off IAC, same thing goes on, no difference with, or without it. started engine without it

Odd that's there's NO reaction.

Check and clean the IAC contacts.

 

[fezder]

cleaned, nothing changed?
i'll clean it again, perhaps i wasn't thorough enough

 

[fezder]

okay, now there was some change: i pushed IAC gently at its smallest retraction, and idle rpm was now even 2k, in same longevity manner. And, i couldn't reset it, it stayed at it's short retraction.
Any help? oh, and MAF was connected during this test, and turned all possible stuff on, radio etc. and it didn't have effect

 

[cowboybob]

OK.

Retracting the IAC emulates a slightly opened condition, which increases idle.

From your description, the IAC mechanism (shaft) may be dirty, causing its action of less than smooth and "sticky".

Try thoroughly cleaning the interior of the IAC (with carb cleaner or equivalent), especially around the shaft area, let dry and try again.

While the IAC is removed, it would be worthwhile to check the resistance of the IAC coil(s). Can you do that?

 

[fezder]

While the IAC is removed, it would be worthwhile to check the resistance of the IAC coil(s). Can you do that?

both were 53.8

 

[cowboybob]

OK. Sounds very high. But, it is rare that a coil's resistance would increase and even rarer that both coils would change by an identical amount.

Google "IAC resistance". Most are considerably less than that. Also note how relatively small variations render the device unusable.

Are there any brands, numbers, etc. on the IAC that might lead you to its identity? And then, perhaps resistance specs?

Did cleaning it make a difference?

 

[fezder]

double checked resistance, it was correct. But, nowhere near 15 ohms google suggests as most, at least what i could find.
only other marking is b298302, apart from russian language & 2112-1148300 code.
couldn't find any specs for this thing....
oh, and i'll test it in couple minutes

 

[fezder]

okay, now it seems to okay, somewhat, idle is still bit high, 2k, but, afaik, it's supposed to be before IAC is in its place?

 

[cowboybob]

OK. Although don't know any auto engine that idles at 2K RPM. More like 750 or so.

How about idle speed after engine is at operating temp? Or with car in gear?

Some engines systems, at cold (or initial) startup are intentionally idled UP to provide additional air to accelerate the heating of the catalytic convertor.

Does disconnecting the IAC power change anything now?

 

[KeepItSimpleStupid]

The IAC is typically like a stepper motor. It could have a seal issue. Do you have a propane torch? If you do, just let some of the gas escape near potential vacuum leaks. RPM should increase a bit unless too much is added, then it will decrease. Do the injection with the IAC electrically disconnected.

I think we can rule out the brake booster diafram. You could disconnect and plug the line. Pedal effort wil COSIDERABLY increase so be careful.

The computer controlled engine removed a LOT of vacuum operated stuff.

 

[fezder]

i test drove it, it settlted smoothly from 2k to less than 1k. so now there isn't any fault. perhaps IAC was just so dirty/corroded it couldn't move?

 

[cowboybob]

i test drove it, it settlted smoothly from 2k to less than 1k. so now there isn't any fault. perhaps IAC was just so dirty/corroded it couldn't move?

Yes. That was one of the suggested problems. Tolerances for the actuator shaft are fairly tight to avoid air leaks. Thus, a little dirt/dust can reduce response.

Good job!

 

[fezder]

Thanks for you guys! this fault has been on/off nature for about 4 years....quite annoying

 

[Ian Rogers]

Glad you sorted it!!

Too many engineers read fault codes and just replace parts.... If the sensor shows a fault, its normally due to some other problem and the sensor is simply out of tolerance...

Well done...

 

[fezder]

Glad you sorted it!!

Too many engineers read fault codes and just replace parts.... If the sensor shows a fault, its normally due to some other problem and the sensor is simply out of tolerance...

Well done...

i just try to do something and ask then from people who actually know something, instead of from those simply say buy that meter and so on....
that tolerance-thing i gotta remember in the future!