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Discussion Starter · #1 · (Edited)
Here's what I'm drivin': 1988 BMW 325is (e30)

The problem:

The car cranks over fine, idles slightly over 1000 and returns to 700-800. The idle is smooth and nice and displays all kinds of e30 goodness. Within a minute, the idle becomes erratic, dips down and back up (never over 1000), and then eventually dies. No amount of throttle will change it - it's like the engine isn't even recognizing my desperate foot dumping on the pedal.

I've tried driving it with no avail. It drives fine for a few seconds, and then quickly the acceleration becomes haggard, rpms die down regardless of where my foot is on the pedal, and idle dips up and down until the eventual death of the car. Turn it back over and it starts fine! Idles fine for less than a minute. Then the monster comes back.

Here is what i've done to it:

replaced the o2 sensor, crankshaft position sensor, fuel filter, fuel pump, fuel pump relay, fuel pressure regulator, air filter, spark plugs and cleaned the AFM with AFM spray. The distributor cap and spark plug wires are from Bavarian Autosport and look fairly new.

I've tried testing the continuity of the throttle position switch using the Bentley manual as my guide. On the 2 and 18 tongs, I get continuity when the throttle is completely closed, but as SOON as I move it even to the slightest degree, I lose continuity. On tongs 3 and 18, I have continuity when the throttle is WIDE open, but nothing else. Is this correct?

On the AFM, the flap moves smoothly with equal resistance. I don't know what else I can do! Please help! This little car is my only means of transportation and walking to work is getting REAL old. Any suggestions will be greatly appreciated.

Thanks
 

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D'oh, You Kids!
1984 633CSi, 1985 635CSi, 1985 325e, 1987 325is, 1993 325is, 1995 318is, 1995 M3, 2003 F150
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The TPS as tested is doing exactly what it's supposed to. It's and on-off switch at idle, and an on-off switch at WOT. At idle it engages the idle control valve circuit to control the idle speed. once the throttle is moved, the circuit is disengaged and the manual throttle takes over. At WOT the upper limit switch tells the ECU that it's at WOT and that changes the fuel map to match.

Have you tested your ICV?
 

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Discussion Starter · #3 ·
Hornhospital,

First off, you're awesome :thumbup:

I have not tested the idle control valve. I have it taken off at the moment. It's the L-shaped gizmo, right? I recently sprayed a bunch of starting fluid in it to clean it out. I read that they don't often go bad, but just get gunked up. How would I test it?

Thank you!
 

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D'oh, You Kids!
1984 633CSi, 1985 635CSi, 1985 325e, 1987 325is, 1993 325is, 1995 318is, 1995 M3, 2003 F150
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31,979 Posts

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Discussion Starter · #5 ·
Just ran diagnostics on the idle control valve.

Got the humming like you mentioned. Also, picked up the proper ohms of resistance on the valve itself. I downloaded the manual that you provided and it looks like I won't be using my Bentley much more.

But after testing the control valve and finding that it works, what next? :dunno:

I just ordered a new vacuum hose set along with the rubber intake boot to permanently take car of the vacuum hose question. How likely could it be the AFM or ECU? If it was the AFM, is there any place online that doesn't sell them for the cost of a kidney? Ok, a kidney may be extreme, but those bad boys aren't cheap.

Thanks for your help! :thumbup:
 

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D'oh, You Kids!
1984 633CSi, 1985 635CSi, 1985 325e, 1987 325is, 1993 325is, 1995 318is, 1995 M3, 2003 F150
Joined
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31,979 Posts
Just ran diagnostics on the idle control valve.

Got the humming like you mentioned. Also, picked up the proper ohms of resistance on the valve itself. I downloaded the manual that you provided and it looks like I won't be using my Bentley much more.
???? That IS the Bentley. :dunno:

But after testing the control valve and finding that it works, what next? :dunno:

I just ordered a new vacuum hose set along with the rubber intake boot to permanently take car of the vacuum hose question. How likely could it be the AFM or ECU? If it was the AFM, is there any place online that doesn't sell them for the cost of a kidney? Ok, a kidney may be extreme, but those bad boys aren't cheap.

Thanks for your help! :thumbup:
You're welcome! What happens when you unplug the AFM while it's running? And I don't remember if the '88 has an idle control computer or not. I think it's controlled by the ECU after '87. A fellow BMW CCA member in our local chapter is having the exact same trouble, but his is an '86 325e. Weird. He's been fighting it for weeks. His fix was something completely bizarre...a washer in the ICV line that has a 1/8" hole in it. :yikes:
 

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Discussion Starter · #7 ·
The link that you posted had three manuals to download. The Bentley and the Haynes wouldn't pull up, but the genuine BMW shop manual did! It's pretty awesome, actually.

With a cold engine, I unplugged the AFM while running. I could not get it to rev past 700-800 (idle). With the engine still cold, I plugged the AFM back in and was able to rev quickly up to 5k (or more) no problem. When I took it out to drive around the block, the same problem crept back up.
 
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