Rough Idle, Check Engine Light Intermittent

I have a 1994 530i that has been running quite well in the three years I've had it. However, recently I've been having a bit of a problem. The car idles rough and almost dies. Then it speeds up (ostensibly the computer is giving it gas to prevent the engine from dying) and then the check engine light comes on. After a short period of time the light goes out and everything seems fine. This seems to happen only in the morning and only when the engine is about 3/4 the way to its normal operating temperature. It doesn't seem to happen in the afternoon even if the engine starts out cold. Perhaps outside air temperature has something to do with it. I don't have a tool to check the fault code, so I'm in the dark as to what this might be. Any ideas?

Reply to
Vernon Balbert
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"Vernon Balbert" wrote

Could be a problem with the cold-temp idle stuff. Could be a leaking intake hose/plenum/manifold. Or, it could be the dreaded Nikasil problem (Google on the koalamotorsport website.)

FloydR

Reply to
Floyd Rogers

On 11/13/2007 4:49 PM, Floyd Rogers went clickity clack on the keyboard and produced this interesting bit of text:

Fortunately, it's not the Nikasil problem. The engine was replaced at

88K for that reason.
Reply to
Vernon Balbert

Air mass meter?

Reply to
R. Mark Clayton

Won't this car tell the trouble code by mashing the gas pedal 5 times while holding your tongue against the roof of your mouth? Turn the ignition to ON but not START, fully depress the gas pedal 5 times within 3 seconds and the code is displayed by the Check light flashing.

I'm not sure of the timing on the depressing-the-gas-pedal stuff, so I expect somebody will jump in here and dial that in for us ... (I am pretty sure you have to hold your tongue in the right position though, or none of this works ;-) )

Reply to
Jeff Strickland

It's probably the mass air flow sensor.

I have a similar problem with the same model.

My son probably can help me with this. Hee hee

Reply to
Bob

The E30's had a test for this. With the air flow sensor feed disconnected, slowly opening the trap door should reflect a consistently changing resistance on a meter. The door should swing with no rough spots or binding. You can look for something stuck in there maybe. Good luck, that's an expensive part for some reason.

Reply to
cosmo

Yeah, tell me about it. $230 is the best price I've seen. I did some research on how mass sensor works and apparently there are about four different ways of doing it, each having a different accuracy. I think that there is some data processing chip involved and that's probably what drives the price up.

Reply to
Vernon Balbert

No, in the case of the E30, it's just a vane with a pot. There are two variants of the thing, one with five pins and one with six, but the pot inside is pretty much the same.

It is possible to disassemble the thing, clean and lubricate the bronze bearings, and clean the pot element with Cailube or Cramolin. Most of the problems with these are caused either by the bearings causing the vane to hang up, or with the pot developing dead spots.

If the pot wiper is worn out, you buy a new sensor box.

--scott

Reply to
Scott Dorsey

Interesting. I like the idea of being able to save some bucks by repairing it. I'll have to make time for it sometime soon.

But "Cramolin"? That sounds almost obscene!

Reply to
Vernon Balbert

I (knock on wood...) fixed mine with one drop of oil on the vane hinge, cleaning the rheostat track with a pencil eraser, and running some 400 grit under the wiper arm.

Reply to
Not Me

Get the codes. Borrow a tool from someone. Pay someone. Just get the codes. Without seeing the codes, you are working completely blind.

--scott

Reply to
Scott Dorsey

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