M20 Stumbling when warm code 1222/1221

[Herr Faust Schinken]

Hi guys,

About a week ago I noticed that my car ( 1988 325is) would run a little rough and throw a CEL when pulling off the freeway to a stop, as soon as I gave it a little throttle the cel would go away. It’s always idled a little rough but this seems to have made it worse.

Yesterday while driving around town in traffic the car started to buck heavily and act like it had no power, I turned the car off and back on and it pulled like a freight train again. It ran fine until I pulled off the freeway 15 minutes later.... same bucking and no power, turned it off and back on again and it was fine again.

When I got home I stomp tested it, classic 1222 /1221 combo.

Things I’ve checked:
Plugs: all under 5k on them and they looked perfect with the exception of cylinder 1 which had just the tiniest amount of carbon fowling. ( very very slightly black around the base of the plug)

Ghetto smoke test with carb cleaner:

Sprayed around the intake elbow, ICV, throttle body, evap canister, fuel injectors etc. No change in idle speed.

Cleaned ICV: no changes, the rotor seems to move freely and the ICV buzzes when the key is on. When unplugged the idle changes a tiny bit but not much.

AFM: sparkly clean, door moves smoothly, when unplugged the engine dies instantly. ( car started throwing 1224 code after I did this a few times)

Valves:

Adjusted to spec within the last 10k, very slightly loud.

O2 sensor:

changed in the last 20k or so, unplugging doesn’t seem to do anything ( no change in idle)

Car pulls well when and has no problem climbing grades at 80mph, the bucking seems to mostly happen when the engine is hot.

Thanks for the help guys!

Edit: engine was rebuilt 20k ago, intake elbow, manifold gaskets, timing belt, C191 ( repinned into a heavy duty water and oil proof Audi/VW style gasketed plug), cap and rotor aren’t particularly old either.

[e30davie]

Have you confirmed the TPS works and is adjusted properly?

Maybe its not realising it wants to go into closed loop idle mode (with the idle switch in the TPS not working properly). and when you come to a stop the idle control isnt working properly.

You want to get a multimeter onto the TPS iteslf and confirm that the idle contacts close when the throttle actually closes, and make sure the wide open throttle contacts close when the throttle is on wide open throttle. TPS is a very simple device but is prone to getting filled with oil and the contacts dont work properly. There is also a small amount of adjustment in the attachment screws.

[e30austin]

What kind of fuel are you running? Does your blue CTS test out within spec?

[Herr Faust Schinken]

The TPS is only a couple of years old, are they known to fail often? I was under the impression that if the stomp test works that the TPS was okay?

I run 91 octane, normally from Costco, my car has an SSSquid chip tuned for the injectors I have and 91 octane.

Also I still need to test the CTS, would that also cause rough running when the car is cold?

[Gregs///M]

A sparkly clean AFM is nice and all but inside the electrical portion, you have 30 years of carbon deposits and copper oxidation. See my thread on AFM's to see why the AFM can cause this bucking issue. Typical signs of failure is sudden and brief power loss, this is because the AFM can output intermittent signal drop, the DME thinks there is lack of air and thus reduces fuel.

[Herr Faust Schinken]

A sparkly clean AFM is nice and all but inside the electrical portion, you have 30 years of carbon deposits and copper oxidation. See my thread on AFM's to see why the AFM can cause this bucking issue. Typical signs of failure is sudden and brief power loss, this is because the AFM can output intermittent signal drop, the DME thinks there is lack of air and thus reduces fuel.

I just ordered a multimeter (finally, After owning an E30 for almost 7 years) so I’ll be checking over all the sensors this weekend. Hopefully it isn’t the AFM, but it wouldn’t be that far out of the realm of possibility

[e30davie]

The TPS is only a couple of years old, are they known to fail often? I was under the impression that if the stomp test works that the TPS was okay?

I run 91 octane, normally from Costco, my car has an SSSquid chip tuned for the injectors I have and 91 octane.

Also I still need to test the CTS, would that also cause rough running when the car is cold?

TPS can be perfect, but if its not adjusted properly it wont idle properly. As i mentined about the ECU wont know you want idle and it will carry on.

[Gregs///M]

TPS will cause an idle problem but not a misfire symptom.

[Herr Faust Schinken]

Update:

AFM:

At about 65 ish degrees ambient with full sun the resistance between Terminal 8 and 9 measures about 2730-2750

When pushing the barn door gently up and down the resistance between terminal 7 and 8 rises and falls smoothly with no perceivable flat spots.

icv:

measures ~40 ohm of resistance between the two outside terminals and ~20 ohm when measuring the center terminal against the outside ones

tps:

continuity between terminals 2 and 18 when throttle is closed, when throttle is opened slightly continuity stops.

When measuring from terminals 3 and 18 no continuity until the throttle is 85-90 percent open.

CTS ( yellow sensor under blue plug)

Around 2050 ohm resistance with a very slightly warm engine. ( Read higher when cold in the 2800s)

CPS reads 538 ohm. So within spec

Also there was a hose coming off the evap canister to the check valve under the throttle body that was slid down on the nipple ( not all the way off) I pushed it back on and zip tied it on, could this have caused some of the issues?

[Herr Faust Schinken]

Test drive around town for 30+ minutes.

car ran great, cleared codes got a 1444 code and so far I can’t replicate the check engine. I’m so ducking confused.

[goalpost]

Did you ever resolve this? i have a similar issue. My power doesnt cut but CEL comes on iddle becomes rough ahd sputters if I rev a few times, it goes back to normal.

[Dafe919]

I just started having this problem as well. Coincidence that it appeared with the warmer weather (It's been near 80 where I am the last week or so)

[Herr Faust Schinken]

Did you ever resolve this? i have a similar issue. My power doesnt cut but CEL comes on iddle becomes rough ahd sputters if I rev a few times, it goes back to normal.

to be honest not really. At one point I disconnect the battery and the problem literally went away. Hasn’t flagged a code since. Still have no clue why it happened. But it seemed to be related to large temp swings in the wether which was odd.