Causes of high idle?

[DrinkCoffee]

I've got a high idle problem on my 1993 325is. It idles at 1000-1100 and seems to be misfiring.

The PO did a manual swap on the car.
There are no check engine codes.

Things that I've done/checked include:
Things that I've tested/replaced are:
Replaced intake boot, manifold/TB gaskets, all vacuum lines that I'm aware of
New O2 Sensor
Rebuilt injectors
New ignition coils
"New" used ECU
Tested TPS
Tested ECT
Tested AIT
Tested MAF
New Fuel Filter
Replaced ICV with a used one, cleaned thoroughly, no change
Replaced Knock Sensors
Adjusted Throttle Body and Cables numerous times
Fuel Pressure = 44psi steady
Vacuum ~ 20hg steady , no leaks
Compression Results: 150 +/- 5 on all cylinders (perfect)

Things that I'm considering:
Vanos Stuck
CPS or CKP
Maf is bad but not completely failed?

If anyone has any insight on this is would really help out. I've been working on the car for about 1 year, but this high idle is something that I can't figure out.

[woods]

Have you tried resetting the dme? Unplug the battery for an hour or so. You can unplug the maf and see how it runs too.

[DrinkCoffee]

Yes, I've reset the dme several times through various diagnostic attempts and have a new one... I've tested the maf in that manner, but I'm not sure if it either has not completely failed yet or if it is good

Nearly everything I've tried for this issue is in that list

[DrinkCoffee]

Bump

[medic1dl]

I see you haven't changed the spark plugs or plug wires. Try those and see if there is any change.

[DrinkCoffee]

Oh shit, those should be on the list.

I've been through some Denso IK20s and have switched to NGK with no noticeable difference.

My mechanic suggest the wiring that leads to the coils (coil-on-boot setup on M50) but I can't find them for sale seperate of the engine wiring harness. Is there anywhere to find these or are they irreplaceable?

[1997328IS]

I'm not sure how off base i am with this but its an idea. I've never driven an automatic e36, but I have had other automatic cars. When you would put them in neutral it would idle slightly higher than when in drive. You said that the PO did a auto-to-manual swap. Was the computer changed from the original one to one that came from a manual e36?

Thoughts?

[DrinkCoffee]

I actually had a thread about exactly this but was not getting any responses (http://forums.bimmerforums.com/forum/showthread.php?t=1560288).

The ECU in the car was fried and threw a constant o2 Code (1221) so I bought a used one. It fixed the code but didn't change the running condition much, if at all. I'm not sure if it is from a manual or auto.

I was wondering if I had to jump some terminals that communicated with the TCM. However, I don't know where to find the Transmission Control Module. The only info on location that I can find is that it should be right about the ECU in the compartment there, but I don't see it there.

Any ideas at all like the one above are greatly appreciated. I'm trying to get this car running correctly before it gets to cold here. I don't have a garage and hate working in the -0 degrees.

[paniolo]

I know it is controlled by the DME ... so I think you are on the right track in either looking at a DME from a manual, or more likely an input (or missing input) from the transmission module that was swapped out.

I assume you have read any relevant auto to manual conversion threads?

[DrinkCoffee]

Yes, I just found out about the auto-to-manual swap by the PO not long ago. I've started to read the gigantic auto-to-manual swap thread.

I've been googling for a few days and not finding much about the ECU differences (since they are both red label 413 it's hard to sort through).

Is the TCM located above the ECU or is that info wrong? I will look into it after class and post back in a few hours.

OK: It looks like the TCM without EGS does go to 4 pins on the ECU. They are:

57: IGN TIMING
47: CRNKSHFT RPM
88: TXD DATA
87: RXD DATA

Do you happen to know how I would go about jumping/fixing these? I would be doing it at the ECU if the TCM is gone, correct?

http://img713.imageshack.us/img713/4861/tcm.png

.

Ok, in Seeker's post in the Auto->Manual Thread (http://forums.bimmerforums.com/forum/showthread.php?p=6375652&highlight=dme#post6375652), he says that you do not need to do anything with the ECU or TCM on OBD1 cars (mine).

So I'm looking at a completely unrelated issue I think..... possibly the maf?

Well I found a new maf for $60 so that's on it's way.

I hate to throw more parts at it but I can't figure this problem out. :/

[DrinkCoffee]

Bump

[woods]

There are really only few possibilities.

Either the dme and icv aren't working properly to adjust the idle, or there is a large air leak after the throttle that the icv can't compensate for. I would put money on the latter. The icv is fully closed, but air is still feeding in. The idle rises but runs lean and crappy. You could probably confirm by checking the voltage to the icv.

Carefully check the icv hoses and anywhere else air could be leaking in after the throttle. A leaky gasket on the throttle body or the intake perhaps. Maybe a crack in the intake?

[DrinkCoffee]

Yeah, I've replaced all of my vacuum lines though. There is no vacuum leak, because the vacuum pressure remains steady on my vacuum gauge, and there is a large noticeable difference in idle when I remove the oil filler cap or dipstick.

I'm on my second ICV which didn't make any difference, and I'm also on my second DME which didn't make any difference in the idle either.

[DrinkCoffee]

Still waiting on new Maf...

Bump

[crazyafghanguy]

i have the same problem, im still looking for answers, lemme know if u find it

[DrinkCoffee]

Well, I got the new maf with no change in idle a while ago. I forgot to update this thread. I got distracted by rebuilding my car's suspension & ignition barrel and haven't been focusing on the high idle. It doesn't seem to be misfiring now, but it could be misfiring rarely.

I can't find any solution to my problem, so I will be re-testing everything from the engine outwards. When I finish my suspension upgrades (soon), I'll be ordering a Dr. Vanos kit, checking the cam timing properly upon installation, and installing new crank and cam sensors with it.

If the idle does not change after that, I will be testing every ecu pin voltage again, pulling the manifold again, testing all output values at the sensors (again), testing fuel & compression again, and also attempting to verify that there are no exhaust restrictions.

I'll try to keep this thread updated (finally nice enough out to work on my car daily). Hopefully I will be getting a video camera soon and can take video/pictures to add.

Obviously, I'm still open to (and grateful for) any new suggestions.

[crazyafghanguy]

theres an adjuster screw on throttle body where it lets the throttle body stay open a little bit during idle, try adjusting the screw because that was my problem with my car.

[DrinkCoffee]

Yeah I've messed with that thing (and the TB cables) quite a few times. Even with the screw all the way out (tb slamming shut) it would only idle around 1000.

[DrinkCoffee]

Bump

[DrinkCoffee]

Bump

[shellndan]

i had to change my crank case vent valve because of a poor idling problem, might be worth a crack.

[DrinkCoffee]

I don't think pre-96 3-series have a ccv. They just have a vacuum line and oil line that run from the crankcase to the TB to be combusted. This is what a bmw tech told me also, but I am almost positive this car doesn't have a ccv? It's a 93 325is

[shellndan]

sorry i would not know model specific. go on to real oem, enter your car details and it should bring up all the bits you have. its handy for just following lines and stuff.

ps i found my problem by spraying a mist of degreaser at the engine bay. if any thing is sucking then it should be obvious. not the most technical or fool proof method but worked for me.

[DrinkCoffee]

That's the odd thing. It seems like I have all of the symptoms of a vacuum leak, but my vacuum pressure is always steady and not bouncy. There is also a pretty drastic change in idle condition when I induce a vacuum leak. I'm pretty sure pre-96 cars didn't have an actual ccv valve but just two hoses that run from the crankcase to the TB.

I've searched everywhere for a leak, but I've replaced all of the vacuum lines and gaskets. It's pretty frustrating because there's not much info out there on diagnosing a high idle on these cars that doesn't involve the icv/tps/vacuum hoses.

[rdaus]

That's the odd thing. It seems like I have all of the symptoms of a vacuum leak, but my vacuum pressure is always steady and not bouncy. There is also a pretty drastic change in idle condition when I induce a vacuum leak. I'm pretty sure pre-96 cars didn't have an actual ccv valve but just two hoses that run from the crankcase to the TB.

I've searched everywhere for a leak, but I've replaced all of the vacuum lines and gaskets. It's pretty frustrating because there's not much info out there on diagnosing a high idle on these cars that doesn't involve the icv/tps/vacuum hoses.


Yo, going to bring this back to life.... I have a high idle at about 1050, I've rebuilt the top end of the engine, because of head gasket failure and valves being burnt (I bought it this way, I don't treat vehicles that poorly), I've put on about 4k since the rebuild. It was a few years ago I did this, then the vehicle sat for about a year and a half. I fired her back up to get working on it again, I don't remember the idle, but I believe it was high then, too. I've done everything to clean ICV, new hoses all around for the rebuild. Timing was set and adjusted perfectly during the rebuild. Compression is solid. Also, though, it runs way higher rpm's than it should.. I'm at a loss, honestly. Mine was not a AT to MT swap. I've done everything that is out there to try. IDK. My next step is a new cluster. Engine sounds like it's revving correctly, speedo is on... not sure here.

Did you ever figure out your problem from all those years ago?