rufrob

Disconnected the afm and it runs well. No back fire. Revs normal.
Reconnect the afm and it backfires and high idle.

190Efan

Sounds like the afm might be the problem.

dolucasi

As far as I know, the pin 3-1 resistance should be ~4Kohm (+/- some tolerance like 15%)
And it should not change with deflecting the AFM plate.
Pin 2-1 resistance should start around 1.5K (+/- some tolerance) and increases up to around 10Kohm around 2/3 open throttle and it will drop slightly to around 7Kohm at WOT.
Yours is measuring quite differently. I am going from memory but I can repeat my measurements if you like. I was away for a week and back with my car as of today. I can do this now.
You need to bottom out on this AFM issue before further diagnosis.

rufrob

I swapped back the original pot.
It was showing the variable reading at 1-2 terminal not 1-3.
I did get 1-10 ohm on the sweep
It wouldn't start. Swapped 2&3 and it fired up
Terminal x 2-6=13.88v
2-3=2.88
But she is idle is surging. 1-2000rpm.

rufrob

After putting it in gear the surging stopped.
Warmed up
2-6=13.39
2-3=2.78
POT 1-2=1.0ohm-10.0ohm

Still no power but drives ok.

dolucasi

Ok, so it sounds like your AFM pot issue is resolved. Perhaps you dug a deeper hole by swapping AFM pots at some point.
Maybe it was also incompatible with your car.

If you want to make sure the wiring is correct, pin1 will be a ground voltage, pin 3 will be +5Volts. Pin2 will be an intermediate voltage that sweeps from 0.6V up to a ~4V with AFM deflection. This is with it plugged in and you will need to stick a copper wire into the connector, or wire wrap the male pins with thin copper strands. Be carefull not to short the pins by mistake.

Now that the POT appears to be back to normal though, we need to get back to baseline measurements.

Report on X11 port pins 3 to 2 and 6 to 2 voltages in all conditions carefully again.

3-2 and 6-2 , ignition on engine off
3-2 and 6-2, ignition on engine on, cold
3-2 and 6-2, ignition on engine on, operating temp, also note if it is steady or fluctuating (sweeping)

The list above needs to be complete otherwise we can not make much progress.

- Cheers!

rufrob

Ing off
3-2=0
6-2=12.55
Ign on
3-2=3.63
6-2=11.93
Engine on cold
3-2=2.88
6-2=13.92

rufrob

Engine hot
3-2=2.83
6-2=13.68
The IACV makes the engine race at 2000rpm when the engine is cd. then fluctuate between 1-2000rpm then almost stall when warm smoke from the hose connected to the valve cover.
When the IACV is disconnected it idles fine.

Think the heater core is bad too. Smoke in the cabin when I turn the fan and heat on. Very little when the heat is shut off.

dolucasi

So let's fix one problem at a time even though I still believe you have multiple issues.
Your AFM pot issues are behind you.
Now the ECU is telling you your intake air temp sensor is busted. What year model is your car? I thought you did not even have an air temp sensor because it was pre-'90.

The surging idle is yet another issue but let's first fix the intake air temp sensor. Assuming you have one, measure the resistance across the terminals with it unplugged and tell me what value you read.

rufrob

I let the car sit for about an hour. Restarted and idle surging is intermittent

Ign off
3-2= 0
6-2=12.52
Ign on
3-2=3.80
6-2=12.46

Engine on idle surging
3.2=2.80-2.82
6.2=12.60

rufrob

The VIN: WDB2010351F745377
Which makes it an 1990

FIN WDB2010351F745377
Model 190 E 2.5-16
Engine 102990 12 001373
Transmission 722417 02 886197
Order Number 0 0 839 18648
Order Location JAPAN
Interior LEATHER ANTHRACITE (271)
Paint 1 ASTRAL SILVER - METALLIC PAINT (735U)
Approx. Build Date 1990-05

Mercedes Benz VIN decoded at https://www.lastvin.com/vin/1735zAJjRRbAmyMQv

rufrob

When I first got the car the ac fan stayed on so I changed one temperature sensor

rufrob

The air temp sensor wasn't connected. Connected now and the same surging
Ign on
3-2=3.84
6-2=12.60
Engine on
3-2=6.82-6.85
6-2=13.72

dolucasi

Super! No more error codes. 50% duty cycle when cold.

Now also tell us the pin 3 - pin 2 voltage when it is hot and surging. Is it also cycling +/- 0.5V?

Once you send that data, I will suggest the next step.

- Cheers!

rufrob

Yes. When hot and surging +~0.5v.

dolucasi

Great, and also inform us of the two voltages at hot and surging:
Pin 3 - pin 2 and
Pin 6 - pin 2.

dolucasi

Also. After you report on the voltages, while it is surging, please unplug the IACV and see if the surging stops and tell us if it goes steady but high idle.
And then while still idling plug it back in and tell us if it stalls.

rufrob

These are the measurements when the engine is on and IACV plugged in

When unplugged the idle stabilized but it hard to restart

dolucasi

My understanding was that those numbers were for cold you just reposted. Let us reset.

In one response once again list the voltages accurately with idling when cold and later when at operating temp. At operating temp list the range of voltage on 3-2 as it is expected to be cycling back and forth every 1-2 seconds.

Afterwards unplug the IACV while idling and surging and report on the RPM. Plug it back in while idling and tell me what happens and if it stalls when you plug it back in.

So I'm asking again what was asked in post #92. I can only help if you send the data for me to help you rufrob.

- Cheers!

190Efan

I don't mean to pile on but we can't help you if you don't supply the information that's being asked for so that we can help you figure out what your car's problem is.

rufrob

Oh no. I thought them a couple of hours ago.
Cold engine on idle at 1600rpm
No idle fluctuations
3-2=6.96
6-2=13.99
During warmup the idle went up to 1900
and would occasionally drop to 6-700 then go back to 1900.

Warmed up running, fluctuating
3-2= 6.91-7.24
6-2=13.74-13.78
Unplugged the IACV, the idle stabilized
3-2=6.82
6-2=13.72
IACV plugged in and the fluctuation restarts

dolucasi

Thank you rufrob.
So you no longer exibit emissions issues, things there appear to be normal.
50% duty cycle warming up. That is just telling you ECU is aware engine is cold, and send out a diagnostic 50% duty cycle signal.
When warm it is fluctuating between 47% and 50% and that is on the money.

Cycling idle like you have I believe has two potential culprits:
(1) Massive air leak. I believe you already reported you checked this and it is not present. If not please check for air leaks
(2) IACV is sticking mechanically because it is a bit gummed up. I feel this is more likely in your case. Your situation is very similar to an episode I had with my car in the past.

Tell us about the history of the IACV:

(1) Have you cleaned it with carb cleaner or acetone recently?
(2) Do you have a spare known good IACV. If so can you swap it in?

What you have now is idle speed control issues and not emission issues.

One other thing to make sure is that the microswitch is working and throttle plate switch is working.
Both are needed for proper idle control. This is a long thread and I'm not sure if you covered these items.

rufrob

First of all,
Thank you so very much. I sincerely appreciate your kindness, patience and support.
I will be sure to pay it forward.
I think I only sprayed some brake parts cleaner into the IACV and called it a day.
I dont remember it especially dirty or gummy. I will use some carb cleaner next.

dolucasi

Hi Rufrob, you are very welcome. Hope to get that 16V running well soon.

So you have fallen into the same trap I fell into about 4 years ago, I had a very random and seldom stall during manual transmission shifting with my car.
I read in another forum back then that IACV's can be cleaned to fix this problem. That turned out to be very incorrect. The IACV was not the culprit.

To make a long story short I sprayed some carb cleaner or brake parts cleaner to clean it up.
Mine did not look dirty at all either to begin with like yours.
Next thing you know I ended up with the same symptom you have now. My original IACV that was perfectly fine got gummed up during me cleaning it.
It was getting stuck with high RPM's and then it would also start to oscillate between high and low rpms.

So instead of trying to salvage it I just went to the Junk yard and grabbed another one. I still have my original and never tried to clean it again. I have it as a spare in case I need it.
I'm sure it can be cleaned but I have never had the reason to put it back in because the JY find has been performing just fine in the last 4 years, 20K miles.

So, if you are going to try to clean it, I would still use a solvent like acetone (brake parts cleaner effectively) probably is best but you really need to flush is well, I would even use a power flusher/sprayer and a lot of it. Give it a bath, and then do it again, and again and again.

Your other choice is to find another known good IACV and swap it in.

- Cheers!

rufrob

Thanks again
I'll try tonight or tomorrow. My poor neighbors. Already got 1 noise and 1 smoke complaint.
I thought the IACV was only operative at idle.
Would it cause the bogging down and lack of power when driving?