89 325i Low Intake Vacuum

[BMW Pit]

Hi people - hope it's cooler than AZ where you are at.
Help! 1989 BMW 325i - I have a little bit of a rough idle I've been trying to correct and am at the end of my rope (sort to say). Here we go.
I have completely rebuilt this thing: new pistons, cam, oil pump etc ... everything was machined (heads, block, crank, rods). It started right up and runs out like a champ - even passed emissions effortlessly. It has about 100 miles on rebuild plus HOURS of running time trying to figure this out.

I've thrown parts at it: O2 Sensor, idle control valve, throttle pos. sensor, temp sender and sensor, new motronic computer, air flow sensor (it has the swinging door and air temp sensor), new injecters, wires, cap, rotor, fuel pump and filter, intake boot ... and gone through the adjustments (per pelican articles) a couple times just to make sure.
NO INTAKE LEAKS have been found. I've used carb cleaner and squirted everything: intake, throttle body, all new hoses.

I hooked up a vacuum gauge - 12 is what I've got (I beleive it should be about 17-20).
I checked for a plugged exhaust system - not even 1 pound of pressure.
I just finished checking the cam timing thinking I might have set it a COG off (retarded timing) ... it's right on valve timing.

Cold start: It lopes a little for about TWO minutes and then gets a bit better once warm. BUT it's still a rough idle with a hint of a lope. It revs up with NO hesitation, restarts easily, doesn't overheat ... but will NOT idle smoothly.

Is there something that needs RESETTING for the overhaul? I'm stumped - the BMW dealer won't help ... they want the money for troubleshooting it.

Okay guys & gals, what have I missed? HELP!!
That vacuum concerns me but don't know what is normal on BMW. She runs GREAT TOO.

Thanks for ANY input.

[bostogrun]

Here is some info on vacume readings:



Vacuum Gauge
Though little understood, the vacuum gauge is probably the best single indicator of your engine's health you can get.

A Little Background
When your car is idling-whether it's fuel injected or carbureted-the throttle plate or plates are restricting the amount of air the engine can breathe in. The pistons are attempting to "suck" the mixture past the throttle. (Of course, in reality, it is atmospheric pressure that is attempting to "push" air into the engine as the pistons travel downward on their intake strokes.) When throttle is closed, vacuum is high in the intake manifold, from the throttle plate(s) to the combustion chambers. By contrast, at wide open throttle there is relatively little restriction to outside air entering the intake manifold, so vacuum in the manifold is very low.

A vacuum gauge reads pressure differences from atmospheric pressure, so the reading is zero in our "normal" sea of air. By convention, vacuum gauges in the US read "inches of Mercury."

Reading the Gauge
Unlike a fuel gauge, the vacuum gauge will keep you entertained with its instantaneous, wide-ranging movements.

When you floor the accelerator pedal, you can watch manifold pressure (another word for vacuum) swing from strongly negative to nearly zero (atmospheric pressure). When your engine is "on the overrun," like using engine braking down a steep hill at high RPM, you'll see really high vacuum readings. Naturally, turbocharged and supercharged will show very different results, with readings swinging into the positive at high speed. IAP's vacuum gauge is not designed for turbo or supercharged vehicles. Your vacuum gauge is also a sort of "poor man's" fuel mileage indicator; when vacuum is low, you are burning more fuel.

Absolute readings are not as useful as changes over time. That is, if you establish baseline readings under a variety of circumstances, you will know what to look for if your engine begins to deviate. Everything else aside, a high vacuum reading tends to indicate a healthy engine.

Having said this, we can make generalities about the readings you can expect. Note that engines with performance camshafts tend to read lower vacuum. Readings are also lower at higher altitudes; the rule of thumb is approximately 1 inch of mercury for every 1,000 feet of altitude gain.

The following readings will not apply to turbocharged engines, or cars with a separate venturi for each cylinder (like Weber DCOE or Dellorto carbs). All readings are inches of mercury (in. Hg.).

ENGINE STATE VACUUM GAUGE READING INDICATION
Steady idle (800-1200rpm) Gauge steady, 17-22 Normal & healthy
Steady idle (800-1200 rpm) Intermittently drops several needle divisions Sticking valve or broken valve spring
Steady idle (800-1200 rpm) Steady, low reading, 8-14 Small vacuum leak or valve timing off; could have low compression/worn rings (verify with a compression or leakdown test).
Steady idle (800-1200 rpm) Steady, low reading, under 8 Vacuum leak (check brake booster, vacuum lines, etc.)
Idle (800-1200 rpm) Needle drops sharply on a regular rhythm Burnt valve, or a valve with clearance too tight
Idle (800-1200 rpm) Needle drifts up & down, along with rpm drift Mixture off or small vacuum leak
Idle (800-1200rpm) Vacuum gradually drops Excessive exhaust back pressure (plugged muffler or catalytic converter)
Idle (800-1200rpm) Intermittent fluctuation Ignition miss; sticking valve
Idle (800-1200rpm) Steady, above 22 Ignition timing may be too advanced
Open & close throttle quickly Drops to about 2, jumps to about 25 Healthy engine
Open & close throttle quickly Drops to 0, jumps to about 20 May confirm worn rings (especially if idle shows only about 15-20) Verify with a compression or leakdown test.

- Mark Lee


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[bostogrun]

It 's got to an intake leak somewhere. It makes sense because it disappears at high rpm when there is no vacume. At idle when less fuel is being metered the air sneaking into the manifold leans out the mixture causing a miss. As the rpm increase and you approcah zero vacume is doesnt make any difference.

[BMW Pit]

Thanks Bostongrun for that much needed refresher on vacuum/readings. I had been using my old domestic-cars manuals for diognostics of vacuum on this 325i.

I DO have a Bently book and never saw anything about vacuum readings until I looked up the 'Compression' limits ... just a few hours ago. As I mentioned, I have searched for vacuum LEAKS everywhere - after reading the article (on several ocassions) on this site (good stuff by the way).

ALL new hoses, sprayed around throttle body, NEW oil fill cap, even sprayed around valve cover gasket and tube from head to block along with dipstick tube.
Am I missing something here?

New stuff: I took comp. test. all above 150 and within a pound or two of each other. I checked CAM timing and it's right on.
What I DID notice this time: I had the vacuum gauge hooked up for cold start this time ... it read 9 to 9 and a half HG. (I thought I did something for it to lower even more) BUT, while sitting thinking and watching as the engine warmed up (about a minute), It jumped back up to 12 HG where it was before. As I mentioned before, as it warms up it begins to smooth out a bit but still with a slight lope. NOT a miss though.

I completely disconnected the Brake booster and them 'One way checks?' in the two lines - plugged off all ports (two at throttle body, one on intake boot) and it did nothing for vacuum reading. So I'm not leaking through the brake system. I removed the air cleaner element - NO change.

I've tried both carbclean and a soap/water mix to spray with. I should hear the engine RPM rise, even if slightly, if I find a leak ... correct?

It's got me stumped - tell me I'm missing something easy ... Please!

In the meantime, tomorrow I'll spray every inch of the intake along with everything else (again) to see if a leak shows up.

Anxiously awaiting ANY suggestions.

Thanks again.

[Jared at Pelican Parts]

Before you do anything else, read this.. Pelican Technical Article: Reading BMW Fuel Injection Fault Codes and see what the car tells you.

The vacuum gauge method probably wont tell you much.

Read the Bentley regarding the throttle valve switch adjustment.

[BMW Pit]

Thanks Jared - I appreciate you all for your input and knowledge ... that goes for everyone out there.
Okay - I read the article. When I first posted here (about a year ago) my problem WAS the 'check eng. light' with the code 1222 - O2 sensor. It would come on after idling for about 40 seconds and go out when revved up. this kept up. I followed the Bently on doing the 'Control unit electrical test'. Carefully, with a Digital tester. The only test that has failed is the 'O2 sensor Preheater' - not showing power at that wire.
Now, to make the 'Check Eng' light stay off, I turned the adjustment screw on the 'Air Flow Sensor' IN, CLOCKWISE and that made it stay off. I guess that's more for emissions than anything else but it worked at keeping that CODE 1222 from coming up (I leaned it out?). Adjustment now is about; Full clockwise in and then out (counterclockwise) around 1 full turn.

I started this project BEFORE I discovered Pelican parts and had the machine shop drum up parts. So, I thought I would check the cam number for application; ITM 056-4610 (ITM Engine Components). Can't find any specs, but I guess it's a STOCK application (Stock VS performance - refering to low vacuum). I thought if it wasn't stock, that might explain the LOW vacuum at idle. I want stock.

Tonight, I rechecked the Charcoal canister and electric valve/sol. again and it's operational. I mixed up a GALLON of water/dish soap and went to spraying, SOAKING everything while watching the Vac gauge - no change in idle or gauge.
I had adjusted the throttle plate upon assembly, and when I installed the new 'Throttle position Switch'. Also tonight, I turned the Throt Plate adjusting screw out so the plate was completely closed - no change on vac gauge.

In that article it mentions a 'Programable chip'. The DME (Motronic Unit) is new - I replaced that TOO. Could this CHIP be programmed wrong and causing this lope/irradict idle? If so, what are my options for checking this?

Tomorrow I will do as you suggest. Read the proceedure and Check the Throttle position Switch' for proper adjustment. I need to readjust the plate properly too.

Again, Thanks!

I'll cross my fingers! Let you know what I find.

[Jared at Pelican Parts]

Messing with the AFM is NOT the way to clear engine codes. You should ONLY start playing with that if you have a CO% meter.

The DME has to be replaced with the exact same part number on the outside of the housing. I have never seen a chip fail.


The throttle plate housing screw will have no effect on vacuum because that's not what controls the idle. Dont mess with it.

Your biggest problem right now is getting the AFM back to normal adjustment. You need to get a hold of a CO% meter and readjust to factory settings.

You need to go to your machine shop and figure out what cam you have. THAT will certainly affect engine vacuum and your idle. If you have some kind of radical profile, you might not ever get it to idle right.

Why did you do all this work to begin with?

put down the vacuum gauge and figure out

1. What cam you have
2. What DME was used
3. Readjust AFM to factory settings with a CO% meter
4. Read the Bentley FULLY regarding how the system works.

[BMW Pit]

I'll explain - I know "messing with the AFM" will not CLEAR the codes. I know how to do that. I was attempting to keep it from coming up (check eng light) with the 1222 code.
My understanding (maybe too simplified) is that the O2 sensor will toss a code when it senses a: Too Rich or Too Lean situation. Do correct me if I'm over simplifing.

Why I did this in the first place:
I take on projects for the challenge, and fun - it keeps me out of trouble too. My neice owned this car and I've always liked it. It quit on her and I sort of inherited it - I was a happy camper. With 200,000 miles on it, I began tearing it down.
#1 rod bearing was shredded and clogged oil filter and oil sump - what a mess. Machine shop checked block, head, and crank - all salvagable. I went to local dealer for parts ... WOW! So, instead, I went with an engine rebuild KIT the machine shop got for MUCH less. Federal Mogul was the majority of parts. I've done MANY engines but never messed with anything new enough to have all this electronics. I prefer the old Iron. BUT I do dig this little car!

I read the theory behind the Motronic system (refering to the throttle plate adj and the AFM adj) and was ... experimenting ... as to how it affected Idle. Yes, the book even states something like it has no affect on etc ..... One of my racing buddies has a machine to set the CO - It's not driven yet and that will be reset before it is. I took note of the original setting and can reset it within a quarter turn of where it was.

CAM: I was informed that it IS a Stock application. The only one they offer for this car.

You got me wondering about the DME and 'Exact' numbers. I pulled out my paper work. I wrote down the number of the original before turning it in (core):Bosch 0261200380. The PAPERWORK for the new one shows an OEM #: 12141748264. Tomorrow I'll look at the actual unit and look for other numbers (don't know if it's BMW or Bosch). From what I can find doing research online, the numbers are the same unit (Bosch VS BMW). What say You?

What about the chip (PROM)? I will call THEM and ask if this thing comes preprogrammed, does it need to be done, or what. From what I've seen (online), I guess a person can even buy the DME where then you use the original chip from the old.

It's a fun little project and I've kept it looking original just shy of polishing every nut & bolt. I'll try to attach a pic.

Thanks for the input - I'll let you know the skinny on the "Programming" question.

[Jared at Pelican Parts]

What say me? I have no idea where you got the DME. BMW doesnt make them. Bosch does. I am kinda curious what led you to replace it. They usually dont fail. I doubt the problem is the eprom.

Based on everything you've said here, I'll bet you that you have a vacuum line hooked up incorrectly and also an AFM which is out of adjustment. Just looking at your pictures, I can see there are no hose clamps on the lines going to the ICV.

The AFM adjustment does NOT change idle speed. It changes idle mixture. Like I said before, you need to check the adjustment of the switch on the bottom of the throttle body and see if it is within spec. The Bentley has the specs. You'll probably have to remove the throttle body to access it.

Get rid of the Fram oil filter and use only OEM (Mann or Mahle).

[BMW Pit]

Looks as if my ‘Post’ last night didn’t come through.

I forgot to mention that I did check the Throttle Position Switch (per Bentley) and it’s operating & adjusted correctly. I rechecked for Purge valve operation – working (power to) and holding (not allowing air flow – vacuum - with key on).



Why DME: I replaced it because the O2 sensor Pre-heater circuit wasn’t operating – everything checked out (wiring/relay) from O2 to DME. I presumed that the preheater not working and the O2 code (1222) at IDLE only was the problem (I understood that Idle/low speed is where that comes into play). Everything else electronically was new, checked out, and adjusted. A SWAG – Silly Wild A## GUESS. Yes, a pricey one. Done deal, I move on.

I called the parts store where I purchased it inquiring about part number/application and programming. As far as the part number - that’s what their book shows. I brought up my concern about the ‘Not Exact Match’ of numbers and they assured me it was the same unit – we shall see. I remember seeing an article on this – a list of their numbers and which ones can be interchanged. I’ll find it again.
About programming: Since it wasn’t the rebuild “BRAND” they push they have no one they can contact for info (they got it from a warehouse/distributor in Phoenix). I opted for the Programa rebuild because theirs was astronomical in price. They were civil about it – I had 90 days in which to return it … and it WAS an electrical item. They suggested calling a BMW shop for answers – I did. Two independent BMW shops – One guy said no but “if I bring it in …” The other fella said that he thought that “the 1989 didn’t have a programmable chip in it”. His quote.
More on this in a moment.

AFM Adjustment: I understand that it’s NOT an idle SPEED adjustment. It meters air (though minute) and I was … experimenting … to see if it would have any affect as to a SMOOTHER idle. Again, I get your message. It’s a Fine Tuning adjustment meant for emissions (and engine longevity one might add). But, like a little kid, I had to mess with it to find out for myself.
I WILL borrow my buddy’s machine and correct that. He should have access to what the parameters/standards are.


Vacuum Lines: There’s only a few.
ONE from valve cover to side of throttle body,
One from bottom of throttle body – through purge valve – on to the canister,
The brake booster lines are correct (took numerous pictures before tear-down),
The short hose for the ICV that NOW has clamps following your advice,
And then the intake boot which is new. Also the intake to fuel pressure regulator.
New dipstick o-rings and oil cap.
I have flushed the gas tank and rigid lines. New fuel pump, filter, and pressure regulator, injectors & o-rings, and rubber lines replaced. Took fuel pressure test – it’s good (Bentley).

More DME - Is it the correct one, and does it need any sort of programming.
Called ProgramaInc Tech support today and left a message – they haven’t returned my call as of yet.
They have a TECH section online and will send them an e-mail tonight. See what happens. According to their website it’s the correct one. BUT, my old unit ended with a 380 (0 261 200 380) – the present one ends with 173. Looking around online, they are supposedly the same unit. When I changed them out there was NO change of any sort.

You caught that – my Fram oil filter.
Mahle filter it is. Mahle - That’s the brand of piston/pin/rings that’s in it.

A car restoration is similar to a boat: It’s a PIT you throw money in to.

[BMW Pit]

Okay - on whether the DME needs to be programmed ...

Two independent shops: One said; "It shouldn't need to be". The second shop said; "I don't believe that year needs to be ...".

The BMW dealership - service writer said; YES - It needs to be programmed to the vehicle".

I was told by other service writers (one from Ford & one from a Dodge dealership - they are aquintences of mine) that "this is BS - They just want your money".
It was suggested that I make them garentee it will fix the problem or they don't get paid and watch them start backpedaling.

I got in touch with Tech at 'Programa' (that was a task) and they said; NO - It's a plug & Play sort of thing. Ready to go.
UNLESS you have some sort of modification (other than stock item) such as a performance cam.

Okay - I leave that DME alone ...

[Jared at Pelican Parts]

Just to clarify, there is NO need to program the DME to the car.It's just plug and play.

[BMW Pit]

Couldn't get a 'Smoke Test' machine so I went another route - I pressurized it!

Some home-grown enginuity.
I capped off the exhaust, disconnected the fuel pressure regulator, and added a paint gun regulator to continually feed 1 pound of air pressure to the entire engine (saw the concept mentioned on-line somewhere). I used my vacuum/fuel pressure gauge to monitor the PSI (old school gauge that only reads up to 15 PSI).

WARNING TO OTHER READERS: As the article stated, you don't want to use much more than about TWO POUNDS of pressure!

The throttle body/throttle shaft.
Soaked it with soap and water and BUBBLES! I also spotted another area - the valve cover just above #3 & 4 injector. Though only showing tiny bubbles, the two surfaces are getting inspected ... with a new gasket. Now, spraying carb-clean on the throttle body (I sprayed a large amount) didn't make a change in idle - but the presure test sure shows it to be leaking pretty bad!

It's not SLOPPY loose, but I can see (and feel) a minute bit of play - throttle shaft/throttle body.

Okay Jared - my next question is; where can I pick up another throttle body? I perused the Pelican site and didn't spot any. Maybe I didn't look on the right page.
OR, is there someone who rebuilds them? SURE don't want to go to the dealer!

Don't know if this will fix the "ever so slight" idle problem, but in theory it makes sense.

Signed: On The Right Track???

[BMW Pit]

Couple of picks - it's crude, but it works.

You can see the bubbles and I didn't even have HALF of a pound of pressure on it at this time.

The other pic: a rubber cap for two inch pipe with a threaded/or bolt-on style valve stem with schrader valve removed mounted to the center. The vacuum/pressure gauge is on the windsheild (out of veiw) connected to the fuel pressure regulator port. and, you can see the other capped outlets/nipples using peices of hose and bolts.

Hey ... it was stuff laying around ... I didn't have to pay a shop ... and it worked!

[JW1988]

Did you ever figure out what the problem was? I am having the exact issue on my 1988 325.

[Milehieagle]

I have the same car and it did the same thing. Turned out to be the oil cap. If it's loose or not sealed properly, it will pull air through the oil cap from the PCV. Basically it's a vacuum leak. Caused rough idle and check engine light in my car.

[brawnDaymnbab]

I am new,wish you a blithesome date!