Check Engine Light on / off

[Googleme]

What's up guys I just bought an e30 because im a new enthusiast. Anyways it's a project 89 325i. My problem is the check engine light will come on for about 5 seconds and then go right back off. Also, when it is in park it idles high but when i put it in drive or neutral the idle is normal.

I've already gotten my hands dirty and replaced some things by myself (0 help from a mechanic) such as
-fuel filter
-head cover gasket
-oil filer
-changed the oil
-new plugs
-air filter
-etc. basically just minor work

So I just have 3 questions.
1) Why does it idle a little high in park, and then idle normally in neutral / drive?
2) What could cause my check engine light to be going on and off?
3) Where can I learn about e30s without having to barrage this forum with questions? I doubt I could just walk up to a bookstore and buy a book on them. I'd like to learn about them without having to just ask a bunch of questions for obvious reasons. Thanks in advance for the help.

[ELVA164]

1) You'll have to specify what "a little high" means, but if it's a small difference like I believe it is, the lower RPM could just be due to the added load on the engine when it is in gear.

2) When is the light going on and off? There are a wide array of things that could trigger a check engine light: anything from a bad O2 sensor to an open fuel cap to a bad terminal in the check panel or an actual problem with the engine. Explaining under which conditions the light shows up might help.

3) There actually IS a book you can buy, it's a Bentley workshop manual for the E30 and it's the most comprehensive source of information readily available in print. Otherwise, PLEASE learn to use the search function on the forums or you'll bear the brunt of a lot of annoyed members for asking old questions. If you search and don't find anything, and if it doesn't seem to be in the manual, that's the time to ask.

Finally, welcome to r3v! :D

[Googleme]

1) A little high means about 1100 - 1300 (an e30 should be idling around 800 or 900 right?)

2) That's a good point the light usually goes on or off when im driving, specifically when I'm accelerating or breaking. It doesn't really come on when im driving but I havent paid as much attention as I should have to be completely honest.

3) Cool thank you. I wonder why Bentley has made a manual on e30s? kinda random lol.

[ELVA164]

1) A little high means about 1100 - 1300 (an e30 should be idling around 800 or 900 right?)

2) That's a good point the light usually goes on or off when im driving, specifically when I'm accelerating or breaking. It doesn't really come on when im driving but I havent paid as much attention as I should have to be completely honest.

3) Cool thank you. I wonder why Bentley has made a manual on e30s? kinda random lol.

That is a little high, haha. One possibility is an idle control valve (ICV) that's on the way out. Here is a picture of its location:


Other possibilities are the throttle position sensor (TPS) or vacuum leaks, but I would read this article because it's a good overview of where to look: http://www.pelicanparts.com/bmw/tech...leshooting.htm

My guess for the check engine light would be an O2 sensor since acceleration and braking are time swhen the air/fuel mixture changes the most. I would start there.

The book is written by Bentley the publisher, not Bentley the auto manufacturer. ;)

[jlevie]

The first thing to do is to use the stomp test to see what fault codes are stored in the DME.

[dnguyen1963]

The first thing to do is to use the stomp test to see what fault codes are stored in the DME.

Then go have a smoke test done on your car. High and erratic idles are often the result of vacuum leaks.

[Googleme]

Cool thanks guys I think I can definitely take it from here.

@ELVA I actually tried replacing the Idle control valve so ill get started on those other things today. As for the Bentley thing I knew it had to be something like that lol