Help with Idle issues

Por_sha911 · Por_sha911's Garage

Well, its been an interesting day.
I have a hunting idle (drops to about 700 and then comes back). I have:
-checked the plugs (clean)
-used a bottle of techtron (ran the tank to empty)
-replaced cap and rotor
-cleaned the ISV with carb cleaner (it didn't rattle like the old egr valves in the 70's american cars but I could hear it moving.
-disabled the ISV at the test block: mostly smooth but still a slight waiver
-unplugged the ISV-waivers
-disconnected the O2 sensor at a plug in the wire above the engine tin (I have B&B's but the O2 sensor is there) - steadier.
-Disconnected the O2 and jumped the ISV at the test block-the most solid idle I can get!
Is this a bad O2? Is there any reason I need the O2 ? (TN is not an emissions state)

I just replaced the wires and haven't driven it yet to see if that changed anything. Any other suggestions?

stlrj · 03-14-2004, 07:08 AM

Quote:

drops to about 700 and then comes back

Rich idle hunt? What happens if you lean it down?

Joe

Por_sha911 · Por_sha911's Garage

I tried adjusting the idle with the ISV test block jumped. No help. Really it seems to run great as long as the O2 sensor is unplugged.
I'm thinking... TN not an emissions state, O2 sensor expensive, runs better unplugged...Why buy a new one?

Steve W · Steve W's Garage

Sounds like the idle mixture may be off, probably rich. Properly adjusted, it would make no difference if the O2 sensor was disconnected or not. When the idle mixture is rich it idles a little higher, the O2 sensor tells the DME to lean it out, the DME leans out the mixture, the idle speed drops lower than the DME is programmed for, so it tries to increase the idle speed by opening the idle stabilizer valve. Because of the delayed reaction of the idle stabilizer valve, when it finally opens up enough to speed up the engine, it has opened up too much, causing the idle speed to go too high, and so the DME wants to slow it down, and thus we go round and round - the oscillation.

Wil Ferch · 03-14-2004, 02:33 PM

Steve:
If Joe is running your chip....does the O2 sensor have any functionality , even at idle? If "yes"...then I could understand your oscillation explanation because of the O2 sensor's actions. If"no"...then I don't understand. The mixture may then be too rich...but this would likely raise the idle rpm...but keep it steady at a higher value because the O2 sensor is not in the loop. What am I missing?
---Wil Ferch

Steve W · Steve W's Garage

Wil, Joe's chip utilizes the O2 sensor at all power ranges, except at WOT - which is why when he disconnects the sensor, it stabilizes. If the O2 sensor tries to provide correction feedback for a rich or lean idle mixture, that's when an oscillation can occur.

Por_sha911 · Por_sha911's Garage

OK, what do I need to do to adjust the idle mixture?

Steve W · Steve W's Garage

Here's a recent thread that has an explanation of adjusting the idle mix using the voltage output from the O2 sensor:

Idle Hunting -- The problem continues!!

Wil Ferch · 03-14-2004, 03:34 PM

Steve:
We can take this of line if you like..but here's my question.

Why does Joe's chip make use of the O2 sensor and mine does not?...both chips from you. Is it because his 87 is a 4k or 8k memory chip using a 28 pin configuration and mine is likely a 2K chip, definately of 24 pin configuration? Just curious...
---Wil

Por_sha911 · Por_sha911's Garage

OK, will a digital multimeter do? Where to I connect it? How will I know if I setting it too lean?

stlrj · 03-14-2004, 04:24 PM

If you lean it to where the idle no longer oscillates, that should be stoichiometric, not too rich or too lean, just right.

Joe

Steve W · Steve W's Garage

Joe, a digital multimeter will do, you would read the voltage off the black lead off the O2 sensor, disconnected from the plug. Set the meter on to read under 2.0 volts, DC settings. The same procedure can be used whether your car has a U.S. or European chip. Wil, yes 87s up are a 4k program, or 8K in the case of the 28 pin chips which runs on a more refined updated program which does recognize the O2 sensor. However it is simple procedure though to run the updated 4k 87 code on a 84-86 DME by moving a jumper adjacent to the eprom socket, enabling the recognition of the full 4k of a 4k eprom. However though, half of the 84-86 DME are already 4k enabled if the circuit board looks like the one attached below. The 2K U.S. program because of it's limited resolution, provides very poor throttle response because it really locks in hard at a 14.7:1 afr no matter what you do - no acceleration enrichment as on carburetors. The only solution is a modified European program such as you have. The 87 up programs because of their extended memory, do not have the same difficulties.

You 84-86 dme is already 4k enabled if it looks like this:

Por_sha911 · Por_sha911's Garage

Not to confuse things but, my `87 has a 24 pin chip.

Lorenfb · 03-14-2004, 09:41 PM

Have to love it!

Por_sha911 · Por_sha911's Garage

Here goes:
-Got the new chip from Steve you-know-who put in, no change.
--Adjusted the engine idle speed with ISV disabled, not change.
---Attempted to adjust fuel/air mix by ear. It wasn't changing.
----Went to a friend's house and borrowed the multimeter. At first I couldn't get a reading at all. Found a broken wire at the probe solder connection. Sigh. Couldn't get a reading on the O2 sensor that made any sense (pardon the pun). We plugged the O2 sensor back in and got readings varying from 1.7 to 4.8. Hmmm. More air/fuel adjustments, same. More air/fuel adjustments, same. Took the meter over to friend's car (also `87 3.2) and the meter showed swings from 2.2 to 8.5=perfect. Doh! O2 sensor is bad.

Here's the kicker: I packed everything up to go home and low and behold, the idle is smoother that the friend's car. Go figure!

Question: Do I leave well enough alone or is there some compelling reason to spend another C-note on an O2 sensor? If the thing is running well, why fix what's not broke? Should I have a 4 gas exhaust analysis? Remember, TN is not an emissions state.

specialtauto · 03-21-2004, 05:45 AM

Most of the time when the idle is seeking that tells tells me the 02 and the emissions control is working. The 02 is trying to adjust the mixture to 14.7 to 1 air o fuel and it's can't because the adjustment is to far off. So, When the car is at normal operating temp, adjust the 02 setting till the seeking goes away. Then you would be very close to the proper balance of air to fuel mixture.

Por_sha911 · Por_sha911's Garage

What about the fuel/air mixture? Does adjusting that affect all RPM ranges or only at idle. The car idles better than ever before but the exhaust at idle smells like its running rich. Any suggestions? (btw-pulled one of the plugs and it looks perfect).