Erratic A/F Ratio under Cruise

[HLxDrummer]

Well I need help with a problem with my car. Under moderate loads (usually around 11 inches of Hg of vacuum) my car will surge a little bit. When I look at the wideband, the A/F will jump from like 13:1 to 16:1, back and forth. It doesn't do it all the time but it makes me feel like something is going bad in the fuel system.

Under WOT, the A/F is solid. At idle it will cycle between 14.0:1 and 15.0:1.

Edit:
Problem is now worse, AF fluctuates from 13:1 to 19:1 at idle and during cruise. I haven't gone WOT since this has happened.

Review:
-In open loop warm up, wideband reads normal going from rich (10-11 AFR in the cold) towards stoich.
-Once the car hits closed loop, the idle and light load AFR according to the wideband will fluctuate from 14-19.
-Occasionally the car will stutter when climbing a mild hill but the AFR wanders constantly while that only happens once in a while.
-Knock sensor is giving no readings at all and that area looks clean and I noticed the rad cap is a little loose - plugs may have gotten wet? What else around there could have gotten wet and caused a problem?
Update: When I drove my car from school to out garage the knock sensor registered a couple counts of knock. I have a new one to put in soon, though.

UPDATE after installing new fuel pump, filter, regulator, '98 ECU, and relocating injector resistor pack to painted surface:
When I plugged in the Tactrix cable, windows asked for drivers. I pointed it to the ecu flash folder x__ (the higher number one). This seemed to work and ecu flash told me is was successful when I flashed. This tune has closed loop turned off so the stock O2s are not adjusting the trims.

Upon starting the car, the AFR fluctuated basically from the start (cold coolant still). It also sounded bad audibly. Before it sounded reasonable but now it definitely doesn't sound right. Fuel pressure is constant at 43 psi so I am assuming the pump, filter, regulator is good. When I first start is it seems to idle ok (timing is constant), then timing starts changing and runs like crap shortly after. Timing goes from 14*-26* according to the LCD boost controller referencing the '98 ECU.



Possible Issues:
Coolant Temp Sensor
-Reads constant according to LCD boost controller through '98 ECU

Fuel Pump Voltage
Just checked the voltage going out of the relay to the pump and had 13 volts. Keep in mind this is with a crappy $10 multimeter that doesn't even read to the tenth of a volt and keep in mind that there is about a foot of wiring and a solder joint after the relay I measured voltage at.

Timing
I have grounded the terminal under the hood with the logger unplugged (this locks in the timing, right?) and there was no change in A/F ratio, still all over the place. This points to fuel or air, correct?

Updated:
-LCD boost controller (referencing 98 ECU) says timing is at 18* when this plug is grounded. The rough idle/sound gets better when I do this, but AFR still fluctuates. Sounds like it wants to stall (low RPM idle)

Unplugged MAF
-Sounds better and timing is locked around 7* according to LCD boost controller referencing '98 ECU. AFR still fluctuates.

Swapped MAF with '97 SL
-No change

Exhaust Leak
-Couldn't find anything.

Wideband
-Recalibrated recently
-Haven't checked yet wiring thoroughly, but the wideband reads normally under engine braking and open loop warm up which makes me think this isn't the problem.
-Put saturated rag around sensor and it was somewhat shaky to 10:1. When we took the rag off, it took a long time to get to 15:1 where it bounced around for a long time. After a while it went to 20:1.

O2 Sensors
-See log on page 2. They are slow but seem to cycle. Have 170K miles on them.
-When I unplugged them, AFR kept fluctuating.
-With new ECU, closed loop is disabled so they should have no effect

Updated:
Front O2 0.01-0.03 (according to LCD boost controller referencing 98 ECU)
Rear O2 cycles fine

Fuel Injectors
-Checked resistance on rear bank: 3.0-3.1 on two of them and 4.4 on the other. I got a new multimeter and the fronts seem to be around 3.1 (meter fluctuates a bit)
-Checked power to the rear injectors with car off and key on - all read 11V.

Resistor Pack
-Relocated to a painted surface. Does this need to be grounded through the housing?
-Grounded it with no change
-Need to check resistances

Rest of fuel system
-New Deatschwerks pump, Fuel Lab filter, Fuel Lab Regulator at 43 PSI base

MAS
-Airflow, temp, baro all read constant so doubt this is an issue.

PTU
-No idea, any pointers?

ECU
With brand new stock ECU:
-Ignition timing is fluctuating but pulse width constant. Plugs on plenum (knock sensor/etc) may have gotten wet and messed up ECU?
With '98 ECU:
-Ignition timing still fluctuates and pulse width is constant.

IAC/TPS
-TPS reads ok and the closed throttle switch works properly.
-With the engine off/cold, I turned on the key to check power to injectors and heard something clicking erratically and sounded/seemed like the IAC but then it stopped. The IAC is brand new as of a couple of years ago. I also unplugged the IAC and it still fluctuates.

Intake System
-Pressure tested a year or two ago and have fixed small leaks since then, but the leaks weren't even bad.
-No vacuum at nipples on TB. Rebuilt TB recently and thought it was weird that the gasket was filled in where it looked like it should have holes corresponding to the vacuum nipples. Figured it was supposed to be that way and installed it. Assuming this is the problem even though it is a factory gasket?

Fuses/Relays
-Doubt this is an issue since a blown fuse would eliminate a certain function of the car, but I plan to check anyway. I checked the fuses under the hood and inside, but need to look up how to test the relays.

eManage
-Unplugged the eManage and problem still persists.

Update: This is out of the car now

Others?

[B-Man]

Something similar is happening to my car. I think it's noise in the TPS signal but haven't fixed it to see if it goes away. My EMU and palm both show a fair amount of fluctuation in the TPS signals at cruise.

[green-lantern]

Have you ever replaced the caps in your ECU?

[HLxDrummer]

Something similar is happening to my car. I think it's noise in the TPS signal but haven't fixed it to see if it goes away. My EMU and palm both show a fair amount of fluctuation in the TPS signals at cruise.

I don't know if I ever logged my TPS while driving but it seems ok... ill have to look into that.

Have you ever replaced the caps in your ECU?

I actually have a brand new ECU but good idea.

[DrGonzo]

What would cause the noise in the TPS signal??? Bad TPS sensor?? I have been seeing it also on my safc and logger. Just figured the electronics where just that sensitive.

[Roybatty]

This can also be an air leak. Post log.

[B-Man]

What would cause the noise in the TPS signal??? Bad TPS sensor?? I have been seeing it also on my safc and logger. Just figured the electronics where just that sensitive.

That's the million dollar question...(for my issues anyways)

[DrGonzo]

This can also be an air leak. Post log.

I don't see how an air leak would cause noise in the TPS signal. TPS has nothing to do with air, it gets it's signal from the position of the throttle plate opening which I guess would be a mechanical signal.

The sensor is a potentiometer which provides a variable resistance dependent upon the position of the throttle plate. I'm guessing that due to age the potentiometer at certain points is worn to the point that the resistance is not constant which causes the fluctuation in the TPS signal. That adding into account engine vibration could all account for the noise I guess.

[Roybatty]

I don't see how an air leak would cause noise in the TPS signal. TPS has nothing to do with air, it gets it's signal from the position of the throttle plate opening which I guess would be a mechanical signal.

The sensor is a potentiometer which provides a variable resistance dependent upon the position of the throttle plate. I'm guessing that due to age the potentiometer at certain points is worn to the point that the resistance is not constant which causes the fluctuation in the TPS signal. That adding into account engine vibration could all account for the noise I guess.

Sorry, was responding to op, afr jumpy @ mid to low rpm.

Sent from garage

[BigTyla]

Poor grounding could also cause TPS noise.

You could also need to recalibrate your TPS. Does it read 100% at WOT? What does it read at idle? Is your idle switch on at idle?