Incendier

Too bad, but at least you're not blowing fuel any more.

Fletcher

O2 sensor going bad, maybe? I've heard this makes for rough idle.

Sab

How do I check the O2 sensor?
Sab.

Incendier

Pull the connection and see if it runs better. (Seriously).

Get the engine up to operating temp first.

Sab

That might be a stupid question, but I'll ask anyway. Where can I disconnect it? I remember that the O2 sensor itself has no removable connectors on it, correct?

Also while investigating this problem further I ran across some mighty scary looking wires that I beleive could be the culprit. I think the wires in question connect up to the injectors. Here a picture:

Any suggestions if that could be the case?
Thanks,
Sab.

Incendier

O2 sensor - caveat, at least on mine - wires come up through a rubber grommet on the right side of the transmission tunnel - passenger's footwell. Pull back the carpet and you'll see it low. They connect via a green push-on connector and pair of connectors that...I can't remember, but it all disconnects.

There are no removable connectors on the sensor itself, just on the wiring from it. If an aftermarket sensor has been wired in, many have to be crimped into place so YMMV.

Scott C. posted the following to me for testing my A/F ratio via the O2 sensor; seems that the basic values could be used to check yours for function:

1. Start car and warm
2. unplug O2 wire near fuse panel (**note - this is the green wire)
3. connect voltmeter to lead coming from O2 sensor (and ground the other side)
4. If reading is consistently below 0.5VDC, then it is running lean..... consistently above 0.7VDC, then it is rich.... IMHO 0.65 to 0.7 is ideal.

As far as the scary wiring - is that by chance the connector to Temp II?

Sab

Hello James,
thanks for the detailed information. I probably won't get to it before the weekend.
I am not sure where these wires lead to, but it looks like 4 or more and they are all completely exposed.
Anyone knows what these wires are all about?


regards,
Sab. <img src="confused.gif" border="0">

Incendier

...and here's where I run out. I don't have one of those new-fangled engines. One of the other S4 owners needs to pipe up.

Regardless, I would clean that situation up immediately and before doing any further diagnosis.

Nice finish on the intake, BTW.

Sab

I found out it actually goes to the knock sensor and repaired the mangled wires. No change, still - rough low idle.
<img src="graemlins/cussing.gif" border="0" alt="[grrrrrrr]" />

Incendier

So back to what Jay and Randy said, as well as the O2 sensor.

Vacuum leak
Idle stabilizer
Injectors
Idle/WOT switches (particularly the idle switch; try adjusting before replacing and make sure it shows continuity with the throttle closed)
Bad signal to the LH/Bad LH

BUT...check out the other topic recently posted (<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=14&t=001312" target="_blank">here</a>) You say it runs fine when cold - check out the responses here for another thought.

This is NOT meant to be critical, but it sounds like you're kinda doing what I sometimes do...taking the crap shoot approach to problem finding. Maybe an organized run-through of the above items would help you narrow this down more quickly.

This s&%t is very irritating - I know; good luck.

John Struthers

Sab,
There were some interesting posts on the Nichols site: <a href="http://nichols.nu/tips" target="_blank">http://nichols.nu/tips</a> if the vacuum, idle stab., idle stab switch search doesn't pan out.
John S. and a very loud Pattycakes
<img src="graemlins/burnout.gif" border="0" alt="[burnout]" />

Jay Wellwood

FWIW - the idle switch on the 87+ models has no adjustment without removing the Intake.

Sab

I changed my O2 sensor , no result.

I went by the shop, they recommended changing the air flow sensor. We changed it several times, some rebuilt once would not run at all and finally about the fifth try I now have one that runs better. The car still idles about 80 RPM's too low (which is not acceptable), but it won't stall anymore.
Does that make sense?

What is the "Idle/WOT switch" and where is it?

This is driving me crazy....

regards,
Sab
<img src="graemlins/drink.gif" border="0" alt="[cherrsagai]" />

WallyP

The idle/WOT switch is a two-part switch unit mounted on the throttle body. It has two functions:
At idle, the idle switch is closed, from just off idle it is open. This tells the ECU that the throttle is closed, so that the ECU can change the mixture for best idle, and cut the fuel flow off at above 1200 rpm.
The Wide Open Throttle (WOT) switch is open until close to full throttle, at which point it closes. This tells the ECU that the throttle is open, so that it can richen the mixture for best power.

To test the switches:
Pull the plug from the EZK and LH ECUs. Hold the plug horizontal, facing the bare contacts, so that the cable comes in on your right end (up thru '89, reverse for '90 & up). Terminal 1 is on the right bottom, 18 on the left bottom, 19 on right top, 35 on left top.

Idle Switch:
Hook an ohmmeter between terminals 8 and 18. With the throttle closed, there should be very low (less than 10 Ohms) resistance between these two terminals on both plugs. When the throttle pedal is VERY slightly depressed, the resistance should change to infinite.

WOT Switch:
Hook an ommeter between terminals 18 and 26. With the throttle closed, the resistance should be infinite, and should stay infinite until the throttle is almost fully open, at which point it should go to a very low resistance (less than 10 Ohms) on both plugs.

WallyP

OK, let's try again ....

First, disregard my last post - the connections given are for the EZK plug, not both the EZK and LH plug.

Here it is again, along with some tests for the MAF sensor - I'm being lazy and repeating another post.

The idle/WOT switch is a two-part switch unit mounted on the throttle body. It has two functions:
At idle, the idle switch is closed, from just off idle it is open. This tells the ECU that the throttle is closed, so that the ECU can change the mixture for best idle, retard the ignition timing by about 10 deg, and cut the fuel flow off at above 1200 rpm.
The Wide Open Throttle (WOT) switch is open until close to full throttle, at which point it closes. This tells the ECU that the throttle is open, so that it can richen the mixture for best power. If this switch fails, the ECU will compensate anyway at very high air flow rates, but not at low air flow rates.

To test the switches:
Pull the plug from the EZK ECU. Hold the plug horizontal, facing the bare contacts, so that the cable comes in on your right end (up thru '89, reverse for '90 & up). Terminal 1 is on the right bottom, 18 on the left bottom, 19 on right top, 35
on left top.

Idle Switch:
Hook an ohmmeter between terminals 8 and 18. With the throttle closed, there should be very low (less than 10 Ohms)resistance between these two terminals. When the throttle pedal is VERY slightly depressed, the resistance should change to infinite.

WOT Switch:
Hook an ohmmeter between terminals 18 and 26. With the throttle closed, the resistance should be infinite, and should stay infinite until the throttle is almost fully open, at which point it should go to a very low resistance (less than 10 Ohms).

Mass Air Flow Sensor (MAF):
To test the MAF:
Disconnect the plug at the sensor, and hold it horizontally so that the three notches are at the bottom, and the two notches are at the top. Terminal 1 is on the left, terminal 6 on the right.
Hook a voltmeter between terminals 2 and 4. Disconnect the LH plug, and jumper between terminals 17 and 21 (numbering on the LH plug is the same as the EZK plug). There should now be battery voltage at the MAF plug. Reconnect the LH plug.
Hook an ohmmeter between terminals 3 and 5 of the MAF sensor. There should be 3.6 to 4.1 Ohms resistance - this checks the hot wire circuit (the actual sensor). Reconnect the MAF plug.
Remove the LH relay and jumper between terminals 30 and 87 to furnish power to the MAF sensor. Remove the LH plug and hook a voltmeter between terminals 6 and 7 of the plug. There should be 1.6 volts dc. Blow on the MAF sensor wire. The voltage must increase - should vary from 1.6 vdc to 5 vdc.

If the MAF sensor fails, the injection time will be about 3.5 ms below 2000 rpm, and about 6.3 ms above 2000 rpm.