Help! M42 running poorly or not at all!

[dude8383]

Here's the story from friday to bring you guys up to speed.

And below is the follow-up of what my friend and I attemped..some quotes are coming from m42club..



Ok the problem started happening on friday..

I came back home from school and got in my car...ran it for like 2-3 min to let it warm up. This is the usual process when i park my car next to the train station.

Anyways I drive around to find a place to eat...as I'm pulling up to a red light in neutral, my car suddenly idles around 600 rpm. It stays steady at that rpm but sounds like it wants to stall..i checked the wires to make sure none popped out, checked the coil packs and even tried disconnecting the AFM but the same thing was happening.

Where else should i look??

Can it be the AFM? The spark plugs and wires are only like 3 months old...so I'm 100% sure it can't be that.

Oh, and the car runs fine otherwise...just the idle is terrible.



FOLLOW-UP

Try the idle bypass hoses, ICV and the throttle body - all worth investigating!

where are the idle bypass hoses?

I checked the ICV and throttle body...

Will answer the whole thing below..

Before you go and blow money, at least test the tps sensor with a multimeter. It might just need to be adjusted. I can't recall if the M42 motors come with tamper markings on the TPS screws or not. If it does, you might want to see if it's been messed with before.

Didn't blow any money on that, i had a spare..

That is the same code I get. I removed the TPS and disassembled it to see if the carbon track was shot, but all seemed fine, and it operated with no discontinuities. I still get the code every now & thenm and the idle sorta fluctuates...but I attributed that to the MAF.

Try resetting the ECU? If it somehow got adjusted then the ECU needs to re-learn the positions.

I tried resetting the ECU..that didn't help


Here's what happened today...

I tried all of the things you guys mentioned.

I switched out the AFM and TPS...that didn't solve anything

This is what my friend and I tried:

Checked the spark plugs and wires...the car was misfiring so we thought that was a possibility..

Removed the AFM and swapped it with one that works...same deal, the car would start and stall almost immediately

We disconnected the AFM and ICV and the car ran BETTER...not great, but much better with both plugged in.

Then we tried plugging them in separately, once with AFM plugged in and ICV disconnected, and then vice versa...same deal.

We're thinking that it MAY be the ECU.. i think that the MarkD chip is sending wayyy too much fuel because the car is running extremely rich at low rpm.

I'm going to try swapping in the stock chip to see if that changes anything.

Otherwise, I'm pretty much out of ideas!



What do you guys think?

[dude8383]

took out ECU today...going to swap in stock chip later in the evening.

anyone have some ideas to diagnose this?

[dude8383]

is everyone stumped??

[O 16581 72452 5]

Dumb question, but is your ICV installed backwards?

Runs similar to my car it seems, bad ICV so i just unplugged it all together, it won't idle for about 30 seconds when it's started from cold, but when the temp. needle starts moving, it idles okay,. check your AFM inside at the contact points, if it's worn, bend the contacts a little. If it had platinum plugs, swap them out for copper core. Turn your idle screw up some.

[dude8383]

Dumb question, but is your ICV installed backwards?

Runs similar to my car it seems, bad ICV so i just unplugged it all together, it won't idle for about 30 seconds when it's started from cold, but when the temp. needle starts moving, it idles okay,. check your AFM inside at the contact points, if it's worn, bend the contacts a little. If it had platinum plugs, swap them out for copper core. Turn your idle screw up some.

i dont know dude, the ICV looks fine...this car has already seen one winter (last year) and it ran perfectly fine.

Which contacts do you mean? The part where the harness screws into the AFM?

[SchnellerVert]

M42's and newer engines like multi prongs.

[dude8383]

M42's and newer engines like multi prongs.

i see...

[O 16581 72452 5]

M42's and newer engines like multi prongs.

Wasn't sure which engines did okay with them, M20s hate them, forgot he'd said it was an M42 or i wouldn't have mentioned that anyway.

Inside the AFM as in remove the plastic cover, buy some silicone (i used Automotive Goop, awesome stuff!), bend the contact points on the potentiometer and silicone the lid back on.

[dude8383]

are you referring to the throttle potentiometer?

i read some threads that say the throttle potentiometer is the TPS..bending the contact points inside the afm may be an m20 thing as well...

im not 100% sure but i dont really wanna up the AFM just yet...ill be switching the markd chip for the stocker in a few minutes..

[O 16581 72452 5]

It's not a big deal to open your AFM and bend contacts man, if you don't want our help, why ask for it? There's a potentiometer in your AFM (Air Flow Meter), it measures how much air comes in the engine with a potentiometer, over time this wears on especially the far ends of the potentiometer from it sweeping, meaning idle and WOT, mine had this happen and many other's on this forum have had it happen, it can cause idling issues, WOT issues, or both.

The most likely problem is your ICV, like i said, your car acts the way mine does because i have mine unhooked all together, your's may not be functioning, mine too runs stupid rich on start up. Bending the contacts on my AFM also helped the car idle better.

The last thing i'd worry about is your chip.

[Eurospec]

Wish I could help man, g-luck!

[dude8383]

It's not a big deal to open your AFM and bend contacts man, if you don't want our help, why ask for it? There's a potentiometer in your AFM (Air Flow Meter), it measures how much air comes in the engine with a potentiometer, over time this wears on especially the far ends of the potentiometer from it sweeping, meaning idle and WOT, mine had this happen and many other's on this forum have had it happen, it can cause idling issues, WOT issues, or both.

The most likely problem is your ICV, like i said, your car acts the way mine does because i have mine unhooked all together, your's may not be functioning, mine too runs stupid rich on start up. Bending the contacts on my AFM also helped the car idle better.

The last thing i'd worry about is your chip.

Ok here's the deal dude...i have an AFM that came from a car that was operating with no problems..i can't be that this AFM is also fucked.

I swapped in the stock chip and the car is actually holding rpm without stalling...i drove the car around and the rpm's would drop sometimes, but again the car was actually running!

[e30_kid89]

what about the O2 sensor??? mine was messed on my 318is and sometimes it would casue low ROUGH idiling and sometine it would just die till i replaced it....also if your car is running better with the stock chip maybe it could be the ECU.....if you dont have an extra i have one i can give u for cheap.

[O 16581 72452 5]

I still say try what i said. :P

I find it very odd that the ECU was suddenly a problem, but cool that your car is running better. I'd personally put the chip back in and try what i said, it's practically free if you have silicone around, may just be a simple idle screw adjustment needed. Try cleaning your ICV, search around.

[dude8383]

Ok, here's the run down.

We tried disconnecting all of the items above same problem was happening.

I took out the Chilton manual (best one out there for m42's) and located the whole electrical diagram for how the TPS functions.

The manual says:

If either switch (in the TPS) fails, the control unit will use air meter signals to calculate idle and full load control and a fault code will be in memory.

Basically whats happening is:

The TPS is not reading proper ohm's at idle and WOT. It should be reading about .8 -1.2 ohms to 3.2 to 4.8 ohm's. We were getting reads of 1.3 at idle and about 4.9 at WOT.

I have adjusted the idle screw temporarily until i get my new TPS unit.

The wiring harness that connects to the TPS switch reads the correct figures.

Make any sense?