92 318I Mystery For Me and 25 Yr Mechanic - United Bimmer Community

**BShadows318I** · 06-26-2009, 03:31 PM

Alright, my dad (the 25 yr mechanic in the subject) and I cannot figure this out, so maybe someone on here has run into this problem.

My 318I have 249,9xx miles on it.

What is happening;

When the vehicle starts up, it runs perfect. When its cold it maxes out its RPMs at ~4200 (Just after 4, before the line for 4500).

As it warms up, it lowers until once at normal running temperature, it maxes out at ~2100 RPM (barely past 2).

My dad and I have checked everything we can except replacing the ECM.
Here's a list...

Air Mass Flow Sensor (replaced)
Crank Shaft Sensor
Cam Shaft Sensor
Oxygen Sensor
Took the Exhaust off just after the header to see if the cat was blocked, ran the same.
Replaced the ignition coil
Replaced spark plugs
Spark plug wires are 2 months old ~ runs to good at start to have one faulting + I know what this feels like and have fixed this recently.
Checked for vacuum leaks

No Engine Codes, well the one we get is unlisted in the Chiltons Manual,
(1235)

Local Engine shops offered to diagnostic it for $90.00/Hr -- if I had this kind of money I'd go buy another e36 318i, since they refuse to give a time estimate.

Any help would be greatly appreciated. Note : My dad is a deisel mechanic and american cars are is area of study, so this is his first BMW too.

**3050rpm** · 06-26-2009, 06:10 PM

I don't understand what you mean by the car running perfectly at startup, and then "maxing out" alternatively at 4200 rpm and 2100 rpm. Is this an automatic or manual transmission? What does it sound/feel like at those rpms? Also, is the redline of the 4-cylinder engine just 4500 rpm, it's got to be more than that.

**BShadows318I** · 06-26-2009, 07:33 PM

Alrighty, it is a manual transmission.

It does this in and out of gear.

When the vehicle is in gear, it will get to the speed alotted for the rpms (say 40 mph for 2100 rpms in 5th gear). It then sounds like the engine is choking, and the vehicle jerks if I try to go over that speed, however if I stay at that speed, it works fine.

Also, when I down shift, this "barrier" goes away, until I push the gas pedal.

when sitting still, it sounds like the engine is choking or trying to backfire but it doesn't quite get there. If you've ever played a video game and just pushed the gas pedal all the way down and listened to the game's interpetation of what would happen without the engine blowing up, my car sounds like that.

Like its trying to go past a point, but it chokes or backfires or runs into a wall.

The vehicle is not actually backfiring as in shooting flames and nothings gettin hotter than usual.

**3050rpm** · 06-26-2009, 11:11 PM

The Bentley manual doesn't list a 1235 fault code either, strangely enough. I'd take a stab and suggest the VANOS system, except I don't think this car has VANOS. Another long shot... are you using specified plugs, or something else?

**BShadows318I** · 06-27-2009, 01:31 AM

Same plugs that I got last time, bosch platinum tipped.

**3050rpm** · 06-27-2009, 09:20 AM

That could be the problem, while the platinum plugs are advertised as super-duper, gee-whiz, and all that, I don't believe they are factory spec, and for some reason non-factory spec plugs just lead to trouble in BMW engines, at least in the 6-cylinder series, and I believe that holds true for the 4-cylinders as well. So spending $10-$12 for four correct plugs might be a cheap solution to your driveability problem.

**BShadows318I** · 06-27-2009, 08:50 PM

I put the same plugs in last year, 100,000 miles ago and they ran fine for 100,000 miles....would this error show up just on these? (note the problem started on the older plugs, than I switched to these newer ones, however they are the same bosch plat tip etc.).

If its possible that it'd just now show up, I'll try to pick some factory spec ones up for the car, however if this is not the issue, are there any other ideas...I mean could it be something wrong with the ECU -- being the problem is pretty much linear, or something that happens at exactly the same moment.

for example; if Temperature is T and my RPMs are R then it'd be kinda mathematic like...

If T = 100 then R's Maximum is 4200 and if T = 210 (or w/e normal driving temperature is) than R's Maximum is 2100?

(if that makes no sense, then don't forget I wrote it...I am a numberic person).

**3050rpm** · 06-27-2009, 10:03 PM

Hmmm, I was afraid you'd say that... This makes the plugs less of a probability. Doesn't eliminate them, just makes them less likely the cause, although I still recommend going back to the factory specs. By the way, when you took the old plugs out, how did they look, anything especially pathological such as oil soaked, encrusted, any electrodes burned away?

The "linear" characteristic of this problem sure is baffling, suggesting not necessarily that the ECU has gone bad (again, possible I imagine) but that something's feeding it funny information. I'm really beyond my very limited automotive knowledge, but here's another thought, for what it's worth, the throttle position sensor

.

**BShadows318I** · 06-28-2009, 02:48 AM

In Response to the Throttle Position Sensor, when removed while running, the RPMs automatically go to 2000, however the problem still occurs based on the heat level.

Also, it does "bog" down when the TPS is off, dunno if that's normal, I figured it was.

The old ones seemed fine, honestly the car runs the same with the new ones and the old ones, so they prolly are still in perfect condition, however they didn't look burnt or oil encrusted, used however.

I'm just worried that with my time running out if I spend more money on this it will be in vain and I'll end up carless which will lead to unemployment(72 miles one way to work in a car that's about to be taken back by my cause I've put 5000 miles on it (8 weeks of part-time work). This is besides the point.

I am trying to find someone to let me test an ECU just to see if that's the problem..only thing I've found is that this world is messed up to where no one trust anyone and they won't take money for letting me test it. (I've offered $20 plus coming and testing it, and letting them watch exactly what I do and offering to replace their ECU if I wreck their's [which I honestly figure and know I wont

]) (This is always kinda besides the point).

3050RPM I appreciate your help and your knowledge.

**3050rpm** · 06-28-2009, 10:25 PM

More guesswork than knowledge, I'm sorry to say... Here's another thought: there was a problem with either the M40 or M42 engines, maybe both, something to do with the timing chain case or whatever, I'm sorry I don't have the details, maybe it was gasket material incompatible with the coolant. Do an Internet search using, for example, "BMW M42 timing chain" for starters, then refine your search as you find pertinent hints. Again, this is a stretch, in that a problem of this type would normally have manifested itself a l-o-n-g time ago, and whether it pertains to your issue I don't know, so this is just a thought.

As to the general condition of the world, I have even less to offer for possible solutions...

Big Evil · 06-29-2009, 08:42 PM

Those plugs DO cause a problem. They're higher resistance than the spec copper core and while they will work, they eventually wear out the coils due to the higher heat loads they create. Find a spec, ohm the coils and wires to see what's what. Your description of the main problem however does sounds remarkably like unmetered air getting past the MAF. You may have an air leak in the vac system off the manifold, the more common problem of hard to find cracks deep in the bellows of the rubber elbow in between the maf and throttle plate. Or how are your brakes? are the hard and stiff? its possible to have a vac leak in the brake booster. ANYONE of those COULD cause what your describing. Lastly, what EGR system is on this car? A leak there when enabling criteria is met (car's warm) will also cause you a bad day. Do you recall anything happening right before the car got hinky? Noises etc?

**3050rpm** · 06-30-2009, 02:23 PM

Phew, sure glad Big Evil joined in, now there's somebody knowledgeable who might be able to help...

Big Evil · 06-30-2009, 10:53 PM

Dude, don't knock yourself. Your pretty good at a lot of this stuff too :-).

**BShadows318I** · 07-02-2009, 01:55 AM

Evil, what would be the best way to test all of the VAC lines? (smoke?)

EGR, I'm a novice, I don't know exactly what that stands for to be honest.

The brakes are newly replaced, however I never replaced the sensor that went out when they went bad.

I've replaced the MAF, changed nothing if it makes a difference, and the elbow from the maf to the intake is fine, checked it multiple times, however it is entirely possibly there are cracks somewhere else.

As far as wierd noises, nothing out of the ordinary, it did do this same problem for a second a couple of days before hand, kinda hit and miss but it went away so I, like a novice, figured it was just because I had used a fuel injector cleaner in my fuel.

Big Evil · 07-02-2009, 03:50 PM

EGR, exhaust gas return. It's a valve used to introduce exhaust gasses back into the intake stream to lower combustion temps and reduce NoX emissions (not always equipped).

Smoke test IS the most effective way to check a vac system, do behind the throttle plate and then in front to check both sides for leaks.

The brake sensor won't keep the car from starting/running but if the brake service light is on cruise control and abs won't function.

If no leaks turn up your last best option will be to take to a shop that does or at least has experience w/beemers and have the sensor data reviewed while the problem is occurring. Could be an ect (engine coolant temp) sensor or equivelant giving a faulty read and causing a limp mode in the ecu (engine control unit)

**BimmerBlooded** · 07-19-2009, 02:18 PM

Hi, I had a similar issue with an E30 325i and my list of suspects were:

1) Temp sensors (there are 2, 1 for inst. cluster and 1 for ECM)
2) Fuel Pressure Regulator, also check fuel pressure
3) Fuel pump
4) TPS
5) ECM, most likely to be the guilty

Let us know how you did,

**BShadows318I** · 07-20-2009, 03:25 AM

We've done all those things, Fuel Pressure is 2 lbs lower than suggested (41lbs vs 43lbs).

Other than that, everything is fine.

Although my father may have only found one of the temp sensors, I'll have to check that out with him..

**David Mc** · 07-20-2009, 08:22 AM

1235 is not a valid fault code. Some models will return implausible blink codes if the ECU has failed or if the power is interrupted during operation. Remove the control units' harness and reconnect after 10 minutes to reset the base values. Check to make sure that your battery is fully charged and then re-test the car to check what fault codes have reset.
This link should help if you don't already have it http://www.pelicanparts.com/bmw/tech...de_Reading.htm