940 940 Turbo runs rich

Volvo 940 running rich

1991 940 SE Turbo. 295k miles. Car is all stock

Family member was driving the car prior to the issue so I cannot comment on what lead up to this condition. All I was told was it was getting terrible gas mileage.
Symptoms:

1. Poor performance. Sluggish acceleration. Got 12.4 mpg on a 150 mile all highway trip. Black smoke out of the exhaust. Low and lumpy idle.
2. Throws five codes

3-1-2: Signal missing for knock-related fuel enrichment

2-1-3: Throttle switch full load setting faulty or grounding short

2-2-2: Signal missing to/from idle air control valve

1-1-3: Fuel trim (Lambda Control) too lean or rich

2-3-2: Fuel trim too lean or rich at idle.

3. The car also does not start with the spiked idle speed and then settle to the 750 rpm range?.it starts as if running really rich at around 450 rpm and struggles to climb to about 600 rpm where it settles. This is especially worse at operating temperature.

What I have done:

1. Cleaned the throttle body
2. Tested TPS switch when I had the throttle body off. Also, distinctive click is heard on cracking the throttle.
3. Inspected for vacuum leaks with a smoke machine. Also inspected for boost leaks with a homemade pressure tester. Found none
4. Tested and inspected the wiring for the engine coolant temperature sensor at the ECU with the ECU connector cover removed. (Pins 13 and ground). Within spec for hot and cold engine according to the FAQ page.
5. Inspected plugs. All four are equally sooty.
6. Swapped the o2 sensor. No change. I am getting about .85 volts at idle and .6 volts is as low as I can get the signal feed to go with throttle manipulation on either o2 sensor. From what I read, it sounds like it should be fluctuating back and forth around .45 volts as the ECU adjusts the mixture.
7. Car has a new catalytic converter
8. FPR tested. Pressure sits at 43 psi. Also swapped with a known good unit with no change.
9. Swapped the ECU. No change. Throws the same codes with either ECU.
10. Inspected and tightened ground straps. Nothing loose or out of place.
11. New plugs/wire/cap and rotor.
12. Timing is within spec.
13. Inspected all underhood wiring. Nothing out of place found.
14. Not sure on LH 2.4 ability to ?learn? or not, but the car sat with the battery off overnight in an attempt to reset it.
15. Swapped the AMM and IAC valve from a donor car. No change.
16. I unplugged the cold start injector and the car runs worse. Was curious if it was stuck open.


I know these Volvo codes are to be taken with a grain of salt, but due to it throwing 5 codes, I am leaning towards a wiring issue?which should be a joy to track down IF that is the problem.
I also have a 1990 740 turbo that I have been using as a donor car to swap parts but I am now at a loss for which direction to go to search for a solution.

Any ideas are greatly appreciated! This one has me stumped. Any major players in the mixture control that I haven?t mentioned or should be aware of?

I would suggest double checking things like the throttle switch. Sure you check it for idle switching but you probably didn't check it for full throttle switching. If there is a short it would tell the ecu to richen the mixture. Another thought is the coolant temp sensor. I'd check it through more than just a couple of check points. A third thought is the signal missing for knock sensing. If that signal is missing the ecu/ezk decides to play it safe with a rich mixture and pulled timing. So I'd try another knock sensor and check the wiring to it.

1) are there any EZK codes, or just 1-1-1 ?
2) does the CEL/MIL work? when did it come on?
3) has anyone else attempted to fix it before you?
4) I don't know if it's possible to mis-connect, but check that the 2-pin connectors go to the correct sensors. IAC, Temp, Knock are all 2-pin.
5) the 2-1-3: "Throttle switch full load setting faulty or grounding short" code is most likely correct and the WOT switch in the TPS is stuck or the wire is shorted to ground. I'd start with this code since it's the most straight forward.
6) I think that disconnecting the battery will clear all codes and reset any learning almost immediately. Waiting a full minute should be plenty.
7) have you pulled and re-inserted the ECU/EZK fuse(s) to clean off any corrosion? I'm not sure which ones these are on a 940.
8) you said that you checked the ground straps, does this include the black ground wire groups going to front/back of the intake manifold?

Swapped the knock sensor and the TPS. The sick car did not have continuity on WOT on the TPS but the donor car did have continuity on closed and WOT...swapped the TB with the TPS switch intact....no luck.

No codes on the EZK side....just the 1-1-1.

Checked both ground groups on the intake and the ones on the firewall...they were tighten. Loosened and re-tightened anyway.

I have owned the car for a few years and put roughly 25,000 miles on it and have been the only one to work on it since...as of now I haven't found any wiring issues but am still searching.

Thanks for the tips.

Check that the wastegate arm is still connected to the actuator. Probably is, but can make car sluggish, tho not likely to run rich.
Can you swap the injector resistor pack from same donor car?

Coolant temperature sensor?

Wastegate Rod looks fine and has the normal amount of preload...Injector resistor pack yielded no change...I think I am going to actually swap the engine coolant temperature sensor to confirm but my diagnosis of the ECT and my gut tell me that's not the problem. We shall see.

0.85V means it is stuck rich.

You could have leaking injectors or possibly a bunk ECM. Or ECT sensor.

Pull the vacuum line from the fuel pressure regulator and check for fuel. The internal diaphragm may have ruptured, this is an easily overlooked fault. I know because I overlooked it for almost six months.

RESOLVED:

Went back through my original checklist and started over. Ended up seeing an oscillation signal from the o2 sensor at idle and going down the road (hooked up the multimeter off the green wire and ran it through the passenger door) after I swapped the ECU...car no longer stinks of too much fuel, has regained the original power it had and the MPG as well. I wasn't looking for o2 sensor signal after I swapped the ECU the first time and must have missed it. 200 miles put down and no codes.