P1126 and P1133
 

Got these codes in May along with the MAF code (?) - don't remember cause it has not come back. 1126 and 1133 have returned. Cleaned the TB and the MAF. Engine starts, hits around 1500 rpm and dies. Over and over. I smoke tested for vacuum leaks and found none (that could be lack of experience, but nothing obvious sucked any smoke). Installed two new Bosch post cat O2 sensors. Same thing. Installed the old MAF that I replaced, and the car runs rough, but runs. No misfires. Unplug the MAF and it idles at a steady 800 rpm cold. MAF is a Bremi from PP. Not certain what info from my MD808 is accurate without the MAF installed. 2000S manual with 50k miles. Suggestions please. TIA.

First thing.
Using a MAF sensors other than Bosch in these cars doesn't seem to work well.
Also make sure you get the proper replacement part number.

From your post I see this is a 2000S
Same thing I have in Guards Red.

When you unplug the MAF sensor the ECU reverts to a fixed fueling map.
The cold start or open loop map I believe. So the car should run sort of ok with the MAF sensor unplugged if all other things are ok.

So simplest things first.
Make sure your battery is in good shape. sounds silly I know.
A marginal battery can cause problems in these cars.

Make sure your plugs and coil packs are in good shape.
Marginal plugs or cracked coil packs can cause miss fires.

Make sure you don't have any exhaust leaks.
Exhaust leaks ahead of pre or post Cat O2 sensors cause false O2 sensor readings.

Make sure you don't have any vacuum leaks.
Vacuum leaks occur after the MAF sensor so that is unmetered air so vacuum leaks screw things up:D
I reread your post and see that you did a smoke test.

You may want to do a fuel pressure test at the fuel rail. Fairly simple to do.
Stalling can be a sign of low fuel pressure.



Couple of questions:
Is the car drivable with the MAF unplugged or does it still stall out?
Why did you replace the post Cat O2 Sensors?

Let us know how you go.

Battery is less than a year old - 13.76 V output.
Plugs and coil packs were replaced 23k miles ago. No misfires.
New O2 sensors cause that was all I could come up with after replacing the MAF (about 2500 miles on the new Bremi).
Still on jack stands - I flushed the brakes as well. I'll have it down today to see how it drives MAF-less.
Lastly, the double row IMS was installed 20k mi. ago. Original looks like new. Just wanted that off the table. :-]

Does the ECU reset every time I change the parameters by removing/replacing the MAF? If that is the case, does it "see" the settings from no MAF, then compensate when I start the engine with the MAF installed, going lean to rich, and essentially flooding the engine? Or does it move the opposite way and starve the engine of fuel? Or neither? IIRC the O2 sensors do not affect things until they reach temperature, relying solely on the MAF.

What voltages are you seeing from the MAF?

I don't believe the ECU resets when you unplug the MAF sensor.
With the MAF unplugged the ECU simply has no way of knowing how much air is entering the intake.
So The ECU reverts to a set fueling map that works under general= average running conditions.
When you plug the MAF sensor back in now the ECU uses the MAF sensors signal to determine the amount of air entering the intake and adjusts fuel to air accordingly.

When the MAF is working properly it is very precise in measuring air intake.
So it is not going to suddenly go from lean to rich or rich to lean just by plugging the sensor back in.

When you have a bad or faulty MAF sensor and you replace it with a good one the ECU does go through a bit of a relearning curve as it adjusts fuel and probably ignition timing to the now proper air intake readings.

This is why when you replace a faulty MAF with a good one the engine may idle or run a little rough for the first few minutes after replacing the MAF.

From what you described in your first post :
If you have no vacuum leaks which seldom cause an engine to stall as you increase RPM
I would look to the new MAF sensor not working properly for the car.
Or a fuel delivery problem. Stalling as you try to increase RPM is a sign of not getting enough fuel.
Stalling can happen from to much fuel but it takes alot.

From 20 frames taken: 1.66 to 2.57V, with most values near 1.80V.

All at idle.

Sample rpm v voltage and MAF kg/h
652 - 1.81 - 54
725 - 2.57 - 46
749 - 2.21 - 51
762 - 1.66 - 44
670 - 1.80 - 37
696 - 1.78 - 39

Thanks

Seems a bit off, you should read 0.9-1.1V with the ignition switched on but not running, and 1.4V idling.

Ignition switched on but not running is .99V.

What is it idling?

Ranges from 1.66V on the low end to a 2.57V high at idle, as rpms fluctuate, but not in sync with the rpms. Voltage and rpms change independent of each other. The 1.66V is not at the lowest rpm and the 2.57V is not at the highest rpm. Idle rpms range from 680 to 750.

That really looks strange.

Took everything apart, cleaned everything, put it all back with great care and some carb cleaner on the connectors. No change. Then the new Bosch MAF arrived. Installed that and my life is now good once again. Seems the Bremi was good for about 60 days and/or 2500 miles. Thanks everyone for your help. The Bremi will be returned.

Glad to hear things worked out.
Bosch is the go to when it comes to things like MAF sensors and O2 sensors.
They developed both so you can't go wrong with them in my opinion.;)

Just wanted to say when you change or clean a MAF sensor don't touch the wire or any part of it other then the base.
Touching the wire or film if it's the film type can screw them up. Natural oils from our hands or something, not really sure what the deal is I just know it happens.