O2 sensor?

[Saabturbo92]

I have hunted around the site for a similar problem....but havent really found what I am experiencing...i have an idle that rises and falls and eventually evens out, more noticable on hotter days...and running the ac also makes this issue more pronounced, coming to a stop light it drops below 900 then up to 1200 back to 700 up agian to 1000 back to 800 and then it comes back and settles at 900...the other part is it does not do this all the time, the only thing I found on the site is that a tired o2 sensor can cause a variable idle, I thought it may be the ICU...any ideas?

[S900t8v]

Don't think the O2 sensor can cause that big of a swing in the idle rpm,

I'd be looking towards an intermittent vacuum leak which the AIC is trying to compensate for, or a faulty/sticking AIC

A friend had the exact same symptoms a couple of weeks ago, turned out to be perished AIC hoses causing leaks.

[Saabturbo92]

The bigger swings are when the air is on i have taken the aic off and cleaned the flap is not sticking and have cleaned the connector as well, i was thinking the same thing, intermittent vacuum leaks i did not think were possible? Well there are a couple aic's at the junk yard....

[Jim Mesthene]

Intermittent vacuum leaks are not only possible, but are designed into the charcoal canister purge system. I think your '92 has a solenoid controlled by the ECU for a purge valve.
I don't recommend swapping parts as a diagnostic technique.
How are you testing for vacuum leaks? How are you testing the O2 sensor?

[Saabturbo92]

Originally Posted by Jim Mesthene

Intermittent vacuum leaks are not only possible, but are designed into the charcoal canister purge system. I think your '92 has a solenoid controlled by the ECU for a purge valve.
I don't recommend swapping parts as a diagnostic technique.
How are you testing for vacuum leaks? How are you testing the O2 sensor?

To be honest I have not, if I have to test for a leak I borrow the tool from my mechanic, As far as the o2 sensor and aic, I need to pull out the volt meter which I am no good at...but my dad is...what is the best way to test those parts?

[Jim Mesthene]

Put a voltmeter on the O2 output wire. It should fluctuate around 0.5 volt.
Spray carb cleaner at suspected vacuum leaks, not forgetting the charcoal canister and manifold gasket. If the voltage jumps, you've found a vacuum leak.

[Saabturbo92]

Well in testin o2 sensor no where near .5 volts it is more like .08 to .23 in range so i guess that will have to go...

[Jim Mesthene]

The O2 Sensor "measures" the mixture. If the mixture is off for any reason, it will show up in the sensor. The trick then is to find out if the sensor is wrong or the mixture is wrong.
If you induce a rich mixture by pinching off the Fuel Pressure Regulator return line, then lean it by pulling the Fuel Pump fuse momentarily, and you see the sensor react appropriately, it's not the sensor.
Have you checked codes?

If you do this stuff exclusively for years, and are familiar with the process without referring to a manual, this diagnosis can be done in minutes instead of hours or days. The unhappy result is the customer says "That stealership only worked on it for 15 minutes and they charged me a whole hour!"
Such are the rewards of professional car repair.

[peva]

Originally Posted by Jim Mesthene

Such are the rewards of professional car repair.

Stop moaning Jim. Saints don't moan.

[Saabturbo92]

After checking the manual it is running lean, i did the carburator cleaner test with no change, i will try to get a change per your last post, the aic resistance is fine 8.2 ohms.

[Saabturbo92]

Oh jim by the way i wish i lived next door to you!

[Jim Mesthene]

Originally Posted by Saabturbo92

Oh jim by the way i wish i lived next door to you!

RETIREMENT
re·tire·ment noun \ri-ˈtī(-ə)r-mənt\
a : the state of being retired
b : withdrawal from one's position or occupation or from active working life
c : the age at which one normally retires (OK, so I'm a little young)

[Saabturbo92]

I think i found the problem hose was splitting on pcv valve cut reset when i switch ac on and off rpms adjust once cant seem to get a change in the readings by pinching fuel reg hose off...could be as simple as the leak from pcv?

[Saabturbo92]

Jim and all thanks for the help in diagnosing without changing parts i did crack the bentley during this process so i have more diagnosis info if i need it...hate when i dont see the simple things first...but in the end its ok especially since i did not guess and buy parts just a little embarrasing...

[Jim Mesthene]

Originally Posted by peva

Stop moaning Jim.

For some of us, it was quite lucrative, but I called it a great business to get out of. It doesn't even pay well anymore.
You don't see many old mechanics, unless they own the Shop and the kids do the heavy lifting.

[gustavm]

I couldnt imagine actually being a mechanic. I love working on my car but how about working on hyundais all day.I dont blame them for charging good money .Ill bet a whole lot of them dont have the clear headed diagnostic ability our man Jim has though!

[2.0ster]

Originally Posted by gustavm

I couldnt imagine actually being a mechanic. I love working on my car but how about working on hyundais all day.I dont blame them for charging good money .Ill bet a whole lot of them dont have the clear headed diagnostic ability our man Jim has though!

I changed a water pump on a 2005 Ford Taurus for my sister in law a couple weeks ago. A little figity but not bad at all. The modern cars are probably a bit easier to work on than our old geezers...

[SteveZodiac]

Originally Posted by 2.0ster

I changed a water pump on a 2005 Ford Taurus for my sister in law a couple weeks ago. A little figity but not bad at all. The modern cars are probably a bit easier to work on than our old geezers...

Once you've cleared all the plastic and snazzy covers which hides the fact that an engine is an engine

[Saabturbo92]

well had to revisit this since I repaired the vacuum lines and replaced the check valve still having an issue with idle after replacing lines and valve swings are smaller anyway.. reading on the O2 sensor varies from -.3 to .6...

[Saabturbo92]

So after reading several times a wack to the aic fixes the problem, i tried it and it did change how my idle responds when turning ac on and off, is this really fixing the issue? I guess time will tell....but should I just replace or wack every now and then? It doesnt seem like a fix but it worked?