M42 idle issues

[jimbolina]

I'm going nuts. I have an intermittent hunting idle.

I've replaced the ICV(twice), O2 sensor(twice), knock sensors, AFM, DME, FPR, fuel filter, PCV valve and hose, spark plugs and leads, all gaskets from intake to head and all exhaust gaskets.

The car drives nicely. It just will not idle reliably. Cold or hot. New parts help the idle for a while but then it just goes back to hunting.

I have 270,000 kilometers on the clock and compression test is good and even.

Please tell me someone has been here before. I need help.

[Panzer_M]

what the idle flux from, I mean rpm wise?

yea my car was there, got a tear down from Brett Anderson/Koala MotorSports in Ohio..although I never got the service records from the prior owner to confirm this.

although I was also told the car was roadable, to find it it had blown front shocks, and a busted balljoint.

[DeanP]

Clogged or dirty injectors can cause an erratic idle due to uneven fuel delivery. A vacuum leak can also cause it. Sounds like you have covered most of the other bases.

[Mr.M]

The rubber boot from the AFM to the throttle body could be cracked. Mine is starting to crack, though it's not bad enough to leak air yet. Yours however, could be, so I would take it off and look it over thouroughly.

[jimbolina]

Thanks for the input.

At it's worst, the idle will swing between 1200 and almost to stall (i.e. lower than 500). Sometimes it just moves between 600 to 1000. It is worse with the added load of the aircon.

Injectors have been serviced and are good.
AFM boot has been replaced along with most of the vacuum lines except for the small lines around the DISA system which are behind a one way valve anyhow. I'm pretty sure it isn't an external vacuum leak.

Could this be a symptom of the sparkplug seals in the valve cover? That's about all I can come up with.

Anyway I'm going over everything again today just to make sure I haven't missed anything. I have to fix this soon or else I'm likely to go postal.

[szed]

woa...weird, I posted a reply earlier in the day and now the post is gone...somethings wrong with the forum...and the "search" too (ahem...)

So I guess I'll post again.

When you start the engine, does it start then bog and want to seem to die the first 5 or so seconds? Then does it continue to be rough or does it smooth out? I had quite a bit of luck solving the problem by cleaning the ICV. I also did the MAF, throttle body and rubber boots/hoses. That helped me for a week then it started the bogging-start-up again, which I think might be my ICV going out. Don't really look forward on spending 170 on a new one. Anyone know how to check it for possible failure?

So try cleaning the ICV before buying/replacing parts. I used CRC throttle body cleaner by the way.

[jimbolina]

I should clarify.

I replaced the ICV a year ago with a new one when my original one failed. I tried cleaning it out when this problem arose but to no avail. So after testing and replacing all the other parts, I though it might be possible that the new valve was now dead so I picked one up from the wreckers, cleaned it and stuck it in.
SAME PROBLEM!

So now I'm trying to find something else that causes this problem. My biggest fear is that it is a problem with the harness wiring.

[OneSickBimmer!]

Check your TPS.
Sounds like aproblem I had a few years back.

[jimbolina]

I've got a multimeter at work. I'll check out the TPS tomorrow.

[amizzi]

i had the same problem on my 95 m42... my issue was that the motor mounds wore wearing out so the engine when torqued moved more then it should... it was a vacuum leak after the bosch sensor.. and before the throtle body... it was hard to see because the hose has those ribs and the crack was between the ribs... if that helps at all.

Clogged or dirty injectors can cause an erratic idle due to uneven fuel delivery. A vacuum leak can also cause it. Sounds like you have covered most of the other bases.

[jimbolina]

Well I found nothing out of place yesterday. I'll have a look over the new AFM boot as well just to make sure it has no leaks.

I'm thinking that the TPS makes the most sense. It's almost like the engine forgets where idle is and trys to find it using mixture as a control. That would also explain why I'm running rich at times.

Ahh well, off to work.

[bigbore]

boot, vac line, tps or a Bad ignition Coil..

i've seen wires have huge arcing at idle, but 100% ok for driving!?
coils could do the same thing!?

[jimbolina]

After testing the TPS today, I discovered that there is no voltage between pin 1 on the TPS and the harness but if I ground pin 1 of the harness to the throttle body, I get 5VDC.
So there is voltage to the sensor but the sensor isn't grounded. I removed it and cleaned the bases of the screw holes (the only grounding point) and still no voltage.
I then tested the resistance between pins 1 and 3 and it was good. I tested the sweeping resistance between 1 and 2 and got nothing.

My conclusion, strange. I'll try to get another sensor to swap in.

[jimbolina]

Well I stuck in a new TPS and the revs seem to drop to idle a lot smoother than before but I still have the hunting. I'll drive it for a while and see if it comes good.

[jimbolina]

Well 300km later and the problem is still there. Any more ideas??

[e36]

bro..i don't think you wqill ever get it perfect. this is an issue that most e36s see and its a huge mystery why.

However, if you do solve it, i would love to see it cause i ahve the same issue.

[bigbore]

Well 300km later and the problem is still there. Any more ideas??

hear any hissing? 270,K on your car... start grabbing Vacume lines & pinching them
checking if they crumble from dry rot & age.

cause all the stuff you've replaced I can onlu think small amount of unmetered air is gettin in from somewhere!?

[szed]

hmmm....bad throttle body gasket and lower-to-upper intake manifold gasket? Have you taken these apart and not replaced the gasket?

[jimbolina]

I have replaced all the vac lines now and the manifold gaskets are new.

I just don't know.

[jimbolina]

PROGRESS!
Today I checked the DISA valve hoses for any leaks while the car was off and I noticed a lack of vacuum in the vacuum canister. I took off the one-way valve and tested it and realised that one of the many mechanics I visited had turned the valve upside down!

I put it in the correct way, refitted the hoses and fired her up. She had a little bit of a hunt but then idled perfectly!

YAY!

[ChristianDK]

Where is the valve located?

Did you also have the start up problems when cold- low and hunting idle until you pressed the gas?

[jimbolina]

Yes I did have that problem.
The DISA valve is in between the two intake manifold halves. If you look at the side of the manifold you will see a black diaphragm with a vacuum hose on it. This is what controls the DISA valve. If you remove this line when the engine is idling and plug the hose with your finger, it should have vacuum.
Follow it down and you will find the switch that controls the vacuum and the vacuum reservoir.
At the other end of the reservoir there is another hose that goes into the one-way valve and then a small plastic hose that runs to the manifold.

If you don't have vacuum at the diaphragm hose, check all the lines, the electrical switch and the one-way valve.

[ldagomez03]

ok, go to the dollar store and pickup a spray bottle, any clean spray bottle will do. fill up with alcohol and spray the engine down. perhaps there is a vaccum leak somewhere. good luck..

[HKBimmer]

jimbolina, if you get this message, can you tell me which way the one way valve should be facing black side pointing up or the white pointing up. Or white side on the vacuum line to manifold side.

[kosta]

+1