e30 idle/sensor issue

[bmtrblu]

1989 325iC automatic. Has funny idle issue. Over the last year, almost all intake parts replaced. Has updated AC, replaced two to three years ago. MAF, ICV both replaced with used parts. New O2 sensor, new coolant temp sensor, new injectors.
Has always idled a bit higher than I feel it should when AC is on, and would sometimes surge when taking foot off of the gas if AC was on. Now however, it started to bog down when the AC was on and it was hot out. Now it is bogging down even with AC off. It will bog down when accelerating, then the engine light comes on, and it refers to the O2 sensor or the lambda sensor when I use my Peake scan tool. I don't remember when the catalytic converter was replaced. I bought the car about ten thousand miles back.
Anyone have any ideas? I can accelerate past the bogging down point, and it runs fine, also it will run fine for a while and then bog down again later, which I feel steers me away from it being a cat problem.
I have also switched out to another MAF (not new) that I had and it runs better and does not seem to bog.... Still got a code though....
Any ideas?

[jlevie]

Intake leaks. Have a shop run a smoke test to find them.

[bmtrblu]

Thanks jlevie, I forgot to add, I did that also. It came back as intake manifold gasket. Had that replaced too. Can it just be bad MAF, or bad ICV to cause this? If so, how to tell?

[NoM54me]

Your AFM (not a MAF) could cause such a problem, but you don't mention the condition of your ignition parts. Everything, from the coil to the plugs, should be checked. If the coil is original, it's time for a new one anyways. Another possibility is incorrect fuel pressure/bad pump, and intake boot.

[brett_duenas]

I had idle and misfire issues a little bit ago; when I disconnected the injector harness (under the intake manifold) I found a lot of corrosion. Electrical contact cleaner solved everything. May or may not help here but I figured I might as well share my experience. Hope you get it sorted out!

[jlevie]

Thanks jlevie, I forgot to add, I did that also. It came back as intake manifold gasket. Had that replaced too. Can it just be bad MAF, or bad ICV to cause this? If so, how to tell?

Was the test properly run? That would mean plugging the exhaust, replacingnthe AFM with a plug & nipple for smoke injection, and holding a smoke pressure (using oil smoke) of 2-4psi for at least 5 minutes. If a leak is found, that leak must be fixed and the test repeated until no leaks can be detected. Was that done?

Other causes are possible, but it makes no sense to investigate those possibilities until it is proven that there are no intake leaks.

[bmtrblu]

Thanks for everyone's thoughts on this. I assume it was done properly, as the shop was one of those looking to make a buck. Intake boot replaced, coil not replaced yet. Don't know age. Also, this only happens when AC is on.... Runs great when AC is off. I did see a steal of a deal today on a new ICV, $56 on ebay with free shipping. New too. So I will replace that just as a matter of knowing it is new....

[AlphaE]

isn't there a load sensor circuit based on amperage draw, that idles up the car?? Well, maybe not the amperage draw, but it knows somehow when there is a heavier load on the motor. maybe that circuit of the ecu is wonky.... try another ecu..

[jlevie]

isn't there a load sensor circuit based on amperage draw, that idles up the car?? Well, maybe not the amperage draw, but it knows somehow when there is a heavier load on the motor. maybe that circuit of the ecu is wonky.... try another ecu..

The system isn't that fancy. A signal from the compressor clutch circuit is fed to the DME. Which increases idle when that signal is present.

[AlphaE]

e30 idle/sensor issue

The system isn't that fancy. A signal from the compressor clutch circuit is fed to the DME. Which increases idle when that signal is present.

Oh yeah! I forgot seeing that on the ac wiring diagram. But, yeah that's how it works. If there is only a problem when the ac is on, then I'd suspect that. But the problem isn't happening just at idle is it?

This is a stretch, but maybe ac comp is dying and seizing/binding up. Disconnect the plug from ac comp. and turn the ac on, that should idle up the motor about 100rpm w/o the actual mechanical load of the comp.

It'd isolate that as part if problem or not.

[bmtrblu]

This is the only place where these cars frustrate me, is tracking down the littlest oddity. That is also what I love about them. Several months ago, I had my hands on another DME, and swapped it out to see if it made any difference with this and it didn't. Looking now also for a good deal on MAF too and see if therein lies the problem. I will also try the little AC test and see what happens....