Over fuelling - Rough idle - can't tune - PLS Help

[ALEX 101 1 Cars]

Car had been stood for a few years, but developed a misfire before I decided to swap over to a new head. it always had been poor on fuel and ran rich (though not as rich as currently). I thought I'd find something catastrophic when swapping the head, but mechanically its all sound and back together with the same / similar issues before I took it apart.

 

What can cause Over fuelling, rough idle (hunting) and ignore that the AFM is even plugged in?

Clouds of rich (eye burning) mixture coming from exhaust and eventually dies (or very slow idle when warm – I have to wind down the throttle stop screw to keep it running).

 

The AFM flap movement and mixture screw doesn’t change the mixture setting. I can even unplug it and it runs without any change.

my Gunsons gas analyser is all over the place up to about 18.0 from 2.0. sometimes down as 1.0 briefly.

 

So far I’ve changed and checked:-

 

A spare known working AFM – No change

ECU Temp sensor - brand new (also tried 1 spare)

TPS – (bench checked)

Fuel Regulator – New

Fuel Pressure checked – 2.9 Bar

Replaced injectors – second hand, made no difference.

New HT Leads

Timing set correctly. (tried advancing – retarding no change in mixture)

Checked wiring loom. (had the engine loom off the car and on a bench) all Seems fine.

Tried a replacement ECU.

Sad bench tested and working.

Tried a spare Ignition module.

Compression test is all good – 12-13 bar across all cylinders,

 

 

The fly lead to the dizzy has been replaced. (Though I had to make my own with a shielded cable) – The type I need is like hens’ teeth for availability.

I have some replacement Bosch connectors that fit inside the Ignition connector plug, so it now goes direct to the ignition module from the dizzy without the middle connector.

I have connected the outer shield wire to one of the pins on the ignition module. Can someone confirm this is correct as I’m not sure?

 

As you can assume from the above I’m running out of ideas.

 

My next theory is that I’m getting interference from the pulse that fires the injectors. But where’s the likely culprit?

If the shield wire is earthed, wouldn’t this interrupt the pulse to the injectors as that pulses to ground?

 

 

 

[PhilNW 66]

Is the misfire on one particular cylinder or random or more than one?

 

Are the plug leads on in the right order? 

[ALEX 101 1 Cars]

6 minutes ago, PhilNW said:

Is the misfire on one particular cylinder or random or more than one?

 

Are the plug leads on in the right order? 

Random misfire, occasional runs smooth, usually on first start up when cold. Plug leads are correct,.

[PhilNW 66]

What happens to the misfire if you diconnect the injector leads one at a time?

[ALEX 101 1 Cars]

53 minutes ago, PhilNW said:

What happens to the misfire if you diconnect the injector leads one at a time?

not much, runs a little rougher than before.

[PhilNW 66]

If the picture is the AFM connector, what are the extra wires?

[DamirGTI 358]

If neither od that stuff you're tried replacing helped or made and difference .. 

Id say it's the wiring .

 

Focus on ECU temp sensor as it's likely the cause .

Continuity test isn't the best , you might have just one or two strands of copper or rotten/oxidized or make-and-break connection somewhere withing the loom .

 

Pull the wiring for the ECU temp sensor directly from the ECU connector , bypass all the OE loom for the sensor directly from the ECU connector to the temp sensor , and see what happens then .

[ALEX 101 1 Cars]

8 minutes ago, DamirGTI said:

If neither od that stuff you're tried replacing helped or made and difference .. 

Id say it's the wiring .

 

Focus on ECU temp sensor as it's likely the cause .

Continuity test isn't the best , you might have just one or two strands of copper or rotten/oxidized or make-and-break connection somewhere withing the loom .

 

Pull the wiring for the ECU temp sensor directly from the ECU connector , bypass all the OE loom for the sensor directly from the ECU connector to the temp sensor , and see what happens then .

Had the wiring off the car and tested the connection direct to the ECU pins. The reading going to the ECU is the same as the reading on the sensor.

The Sensor is brand new. I have 2 spares both read similar resistance.

 

I haven't checked if its getting power, something I'll have to back probe when running. Power is getting to the AFM, with a good earth. It looks like it's fed from pin 10 on the ECU.

[DamirGTI 358]

Still , id pull up bypass signal wire directly from the ECU to the sensor .. and add battery earth to the sensor too , that'll rule out the wiring side  .

It might've been good while testing the loom on the bench , but once fitted on the engine twisted/bent and add vibrations it could be losing signal ..

 

AFM , possibly you have two with which someone played with the spring tension .

Mark position and for a test wound up the the spring a bit so the flap opening tightnes up .

Mixture screw is usually set 7 to 8 turns out from fully in .

 

All the engine management items right for a 1.6 without mixed up stuff ? 

 

Check if you maybe mixed up the SAD and CTS connectors as they're both 2pin ..

 

Fuel pressure , sadi it's right but still id try to disconnect the return line to the tank , and run it separately from the FPR in an canister .. kink or blockage in the return line can make it run rich too .

[ALEX 101 1 Cars]

27 minutes ago, DamirGTI said:

Still , id pull up bypass signal wire directly from the ECU to the sensor .. and add battery earth to the sensor too , that'll rule out the wiring side  .

It might've been good while testing the loom on the bench , but once fitted on the engine twisted/bent and add vibrations it could be losing signal ..

 

AFM , possibly you have two with which someone played with the spring tension .

Mark position and for a test wound up the the spring a bit so the flap opening tightnes up .

Mixture screw is usually set 7 to 8 turns out from fully in .

 

All the engine management items right for a 1.6 without mixed up stuff ? 

 

Check if you maybe mixed up the SAD and CTS connectors as they're both 2pin ..

 

Fuel pressure , sadi it's right but still id try to disconnect the return line to the tank , and run it separately from the FPR in an canister .. kink or blockage in the return line can make it run rich too .

Some good suggestions. I'll check the fuel return.

I checked the wiring on the bench Tuesday, so wasn't a while ago. TBH the Loom from the ECU was in good condition with only one brittle wire going to the SAD, which I've replaced. I'm quite positive it's not got damage since fitting it back in.

 

I've not mixed up the SAD and CTS. The CTS is the blue connector. The CTS connector must be working to a degree as the engine cuts out if I unplug it. 

 

All 1.6 management. (blue injectors correct AFM ECU dizzy Codes)

 

AFM Was brand new in 2012, never been opened. I also have a spare (looks like its never been openend but clearly older, the box I stored it in since 2012 said tested working!)

Adjusting the AFM screw does nothing! the same unplugging it. 

 

I'm still convinced i have interference somewhere, possibly from the botched fly lead.  Or my coil has an internal fault or Ignition module needs a better earth?

I've not had the ignition wiring out, it gets a bit mixed up with the rest of the loom, even with the dash out it looks a tangle mess.

 

One strange characteristic i did notice, the RPM needle on the dash sometimes has a delay when first starting the engine, maybe related or is this normal? 

 

 

Edited March 19 by ALEX

[DamirGTI 358]

Jetronic ECU is an old analogue unit , thus interference wont make it do any weird stuff .. 

If it was Motronic , then yes it might . 

 

Many of us used to run Jetronic management with that fly lead completely rotten , even without the shielding bit connected .

As long as the two pick up coil wires are good , it starts up and runs - no worries !  .. same for the module , if something was missing it wont start or it'll misfire pretty much all the time . 

 

Rev counter delay immediately after the start up , i've seen before , it's either down to the clocks or the coil maybe or the old degraded wiring aka weak signal .. anyhow neither one got any better nor worse just some do it some don't .

As the rest of the stuff , irrelevant for this specific issue .. rapid bouncing needle along with misfiring though is a sign of a module bad , or going bad (overheating) .

 

Yours sounds like typical over fueling , misfiring/rough running for a few seconds on the first cold start is (very likely) because of too much fuel injected .. especially combine with what you said happens afterwards - obviously runs rich post cold start too . 

 

Seems like for some reason the ECU gets wrong signal via CTS , like the engine/coolant is at sub zero degrees , and hence increases injector pulse on cold and post cold start too .

That's why my suspect was the CTS wiring - try direct bypass from the ECU and good clean earth and see if it makes any difference .

 

You can add trimpot resistor in parallel on the CTS wiring and wound in or out some resistance in order to fool the ECU , to make it run more lean or rich as you wish , but in this case that'll be just masking the real problem . 

Anyhow , i had to do that on my Motronic 3.1 conversion , as it did the same during the cold start - misfiring and running rough till it warmed up a bit . (cold start map within the ECU was not suitable with the engine , needed remapping for which i couldn't  find someone with as grayish or shiny polished bald head as possible , thick vision correcting glasses and heaps of arthritic joints all over the place .. so i rolled up with that bodge via simple on/off button under the steering wheel) 

Edited March 19 by DamirGTI

[SRDT 232]

On 3/19/2026 at 11:00 AM, ALEX said:

Fuel Regulator – New

Was there absolutely no change after changing the FPR?

You could have a fuel leak to the manifold via the intake pressure compensation line.

[PhilNW 66]

On 3/19/2026 at 12:10 PM, PhilNW said:

If the picture is the AFM connector, what are the extra wires?

Did you have a look at this? There should only be 4 wires (see item 1 on your wiring diagram)

 

Might be worth getting one of the small digital oscillascope (see Amazon or similar) to check voltage and signal strengths, I have one useful where a voltage meter cant respond quick enough.

 

Edited March 20 by PhilNW

[ALEX 101 1 Cars]

1 hour ago, PhilNW said:

Did you have a look at this? There should only be 4 wires (see item 1 on your wiring diagram)

 

Might be worth getting one of the small digital oscillascope (see Amazon or similar) to check voltage and signal strengths, I have one useful where a voltage meter cant respond quick enough.

 

That picture was of the 7 pin ignition amplifier connector (only 6 pins are used.)

 

I worked though the checks in the Haynes AGAIN, Also The ECU Temp sensor connector is getting 12v (10v when cranking). SAD also getting a feed when cranking, earths are all good.  

Though I must have disturbed something as now its struggling to start, I've just checked the fuel pressure again and it holds 2.9Bar and goes to 3.0 when I can hear the pump. Fuel pressure reg is fine as I can suck on the spring diaphragm.

 

The ignition module that was fitted when i bought the car seems to be the wrong one, but it must have be fine as I ran it for years, It has a Fairchild part number 0227 100111 MTR01 and has all 7 pins. It's coming up for a BMW!?

I bought 3 Bosch 0227 100 123 on ebay. I tried the first one and it didn't change the symptom so thought it must be something else, 

I've measured the earth connector on one ignition module to its (ally) mounting back plate  (The pin the yellow wire in my photo goes to) one shows continuity and the other doesn't. Also the BMW doesn't so not sure what's correct? 

I thought it was just an heat sink, but my mounting plate has a a few ground wires attached to it one is connected directly to the battery neg.

There's thermal paste i believe behind the ignition module, does this need to be conductive?

 

[PhilNW 66]

It needs to be heat conductive not electrically conductive, Renew the paste if it has been disturbed.

 

What sort of resistances are you getting for the earths?

Edited March 20 by PhilNW

[SRDT 232]

New-ish 7 pin black Bosch 123 modules can be problematic when used on Motronic ECUs but should be fine elsewhere. Original old "made in germany" six pin blue modules are obviously 100% comparible. I have also seen a few white 123 modules on ebay, aside from the colour they look exactly like the blue ones but I have no idea if there is some meaning behind the colour change.

[DamirGTI 358]

Try this , 

 

Leave the CTS so you don't need to mess around with coolant leaking or draining . 

Unplug the CTS connector and plug in it that other spare CTS which you have , make an cup of warm water of say 50-60C , dip the CTS connected inside the cup wait a minute and try to fire it up .

 

Try on first cold start after left standing over night . 

See if it then starts up normal without misfiring/rough running , that'll show if it even uses CTS signal or not .

 

Nothing to do with the ingition module that might make this happening really .

 

You might play a bit with dizzy advance/retard .

 

Does the ECU maybe have one of those "super chips" mods inside ?! They used to solder them on the board and tweak injectors pulse width .

 

Do you maybe have one of those nasty Alibaba/Aliexpress knock off fuel pumps ? 

I remember we've had someone here with similar issue , all kinds of stuff tried to no avail and it the end it turned up to be the bloody Chinese fuel pump !

Edited March 20 by DamirGTI

[ALEX 101 1 Cars]

Stil no luck with this after spending most of my weekend on it. Misfire still there :(

Cleaned the Ignition module mating face and remounted thermal paste (typically used for CPUs / Fan heatsinks)

Cleaned up the body earth near the front headlight

Replaced the coil with a spare I had, and replaced its spade connectors.

I think I found the cause of the Rev counter delay. an earth connector on the steering column had partially come unplugged.

Changed my FPR back to the new one I bought. 

 

Could someone confirm my AFM connector is wired correct. The Yellow and blue wires. One is the flap the other is the Air temp. I had these out and replaced the the connectors. 

 

Dashboard is now fully out so I have easy access to all the wiring, 

I've currently unplugged everything from the fain fuse board and blasted it with the air line (Thought was I'd dropped a piece of wire or something in one of the sockets). still to go back together yet.

In the process of partially removing the Toad alarm -connected to the engine wiring to eliminate an immobiliser fault..

Next plan is to probably remove the engine loom again, probably replace all the connectors going to the ECU. They've been spread open a little with my probing of the multimeter.

 

Also lastly. The signal wire (Cyan in colour -shielded quite thick) from the coil to the ECU, Goes though a multi plug that split to the Tach relay. Should one end of the shield wire be connected to an earth? Mine is just cut either end. 

 

Ignition modules I have. The black Fairchild one came with the car. The one under it has the same part number as the other blue ones but looks slightly different. This didn't earth to its back plate, same as the Fairchild one. The one with the 1.6 written on it is the one i fitted before cleaning it up with new thermal paste..

Insert other media

Edited March 23 by ALEX

[PhilNW 66]

Wiring diagrams with pin numbers and colours can be found here

 

http://prepparts.free.fr/docs/doc2ter.html

 

use Google translate 

 

Edit

 

Think you have to go back to basics , is the misfire ignition or fuel related. Is it on one cylinder or common to across all cylinders?

 

Found these useful for ignition issues https://www.tooled-up.com/sealey-vs5261-4-piece-ht-tester-set/prod/142255/?manId=sealey

 or digital oscilloscope I mention before

Edited March 23 by PhilNW

[ALEX 101 1 Cars]

Misfire is fuel related. 

 

Thanks for the link. 

 

I don't want to get too excited here  but I think I might have found the problem? 

 

I'll report back.

 

Edited March 23 by ALEX

[PhilNW 66]

You have probably swapped most of the components , AFM, temp sensor etc.

 

You have just triggered something but many moons ago I had a intermittent misfire which I traced to a connector underneath the inlet manifold where the 4 leads from the injectors come together. It is not easy to get to and pretty corroded as I recall

 

I assumed at the time it was some form of common earth for the injectors but from the french wiring diagram the power to and from injectors goes to different pins on the ecu.

 

Worth further investigation if you have not done so already.

[ALEX 101 1 Cars]

I'll check tonight, but according to the data sheet from that link I have the earth and power feed mixed. pins 4 &5

Brown, green, yellow, grey =  brun, vert, jaune, gris.

I remember checking this with the photo in the Haynes Workshop manual 18A and M18.

 

 

[ALEX 101 1 Cars]

Haynes is showing 18A on pin 5 and 18M on pin 4. 

 

Could someone do me a favour and confirm to me what order the wires go to the AFM.

 

[PhilNW 66]

Sorry No wire numbers visible

 

Edit

French diagram shows 

 

Pin 5 - M18

Pin4 - 18A

Pin3 - Blank'

Pin2 - 7

Pin1 - 8

 

Edited March 24 by PhilNW

[ALEX 101 1 Cars]

40 minutes ago, PhilNW said:

Sorry No wire numbers visible

 

Edit

French diagram shows 

 

Pin 5 - M18

Pin4 - 18A

Pin3 - Blank'

Pin2 - 7

Pin1 - 8

 

Cheers for taking the time helping.

 

Certainly a mystery though as Haynes is showing the power (18A) and Earth (M18) the other way around. I've used that page in the Haynes numerous times in the past (when the car ran fine) never considered it to be wrong. I'm thinking maybe it doesn't matter.

 

Currently Its not even starting after removing the fuseboard and refitting it. I've either missed something out, blown something or made the bad connection worse. 

I'm at a loss at which way round to wire the AFM though, also I'm not sure why my wire is brown and not white. blanc (white) fits better with the ba on the diagram than the brun (brown) i have.

I have re-pinned this connector before (2012), maybe i replaced the wire back then?

 

Edited March 24 by ALEX