Why does my 325i idle at 1400 rpm?

[Vincent Brick]

For the last year or two my 325i has been idling at 1400 rpm, only very seldom will it idle at a more reasonable 1000 rpm. This is now a problem because i need to have the car smogged but I don't think it will pass if it is idling at 1400 rpm (not really sure, new to CA and that stuff is a total mystery to me).


I have tested it for vacuum leaks, and it did have a very tiny one from the crankcase vent hose off the valve cover, but I replaced that hose with no improvement. I used to have 17# injectors in it, but never got around to a tune, went back to stock and it runs better and seems to idle at 1000 more often, but not enough. I have also tried three other ICVs with no change (one actually made it idle even higher).


What should I do? I need to get the car smogged ASAP so I can hopefully get my registration sticker in the mail before it expires. Thanks for any advice.

[MrBurgundy]

Check your TPS

if it doesn't send a signal to the ICV when the TB is closed, the ICV will stay wide open, causing this problem.

[Vincent Brick]

Does it send signal directly to the ICV, like can I check a wire for continuity? As of a year or so ago the TPS tested good, but I will try it again. I've got the 1991 electrical troubleshooting manual, hopefully I can make some sense of it.

[MrBurgundy]

I guess you can start off by testing the adjustment on it, since you don't need anything exvept your ears.

Go under the hood and open the throttle very slowly. As you're opening it and we're talking like 1 or 2 mm, you should hear a click.

[Vincent Brick]

I have traced the high idle back to a poor connection at the TPS plug, in case anyone in the future experiences similar. Thanks to all that helped.

https://www.r3vlimited.com/board/showthread.php?p=4896594

[MrBurgundy]

awesome, it was as easy as that

[Idrisu]

my problem is the opposite, I idle at 500 rpm

[Vincent Brick]

awesome, it was as easy as that

Yeah, thanks for the help. I'm probably not as big of an idiot as I come off, I've worked on a bunch of these cars and know them pretty well, I'm just a bit slow tbh and don't have a lot of confidence.

my problem is the opposite, I idle at 500 rpm

Is your tach accurate? Because I doubt mine is. M20s are supposed to idle around 800, where even when mine is idling properly it still shows 1000-1100. When I stated it was idling at 1400 it's probably idling at more like 1100 when it should be at 800. I don't think a 500rpm idle is really possible, unless it is running really rough on the verge of stalling.


I have been intending to research if E30 factory tachs can be user-adjusted in any way.

[kronus]

they cannot be user-adjusted. they have coding plugs - it might be that you have a 7K rpm redline tach with an eta (5K rpm redline) coding plug in it, which would cause your tachometer to read ~40% high.

you can verify the actual motor RPM with a timing light that has a digital readout.

[Vincent Brick]

they cannot be user-adjusted. they have coding plugs - it might be that you have a 7K rpm redline tach with an eta (5K rpm redline) coding plug in it, which would cause your tachometer to read ~40% high.

you can verify the actual motor RPM with a timing light that has a digital readout.

That is disappointing to hear, I was hoping maybe even the needle could be removed and reinstalled. I doubt I have the wrong coding plug, I've talked to the last several owners of the car and none of them really messed with any eta stuff but I'll check it next time I have the cluster out.







I figured out the source of my idle issue, but not yet how to correct it. Cleaning the terminals with a file made it seem like it was fixed last night, but now this morning I try to go get it smogged and idle is back up to 1400, it will only drop to 1000 if I press down on that connector. Next is to try bending the pins I guess and see if i can get them to make better contact. Maybe I will try to use a piece of small wound guitar string to clean the female part of the connector, since it is too small for even my smallest of files.

[MrBurgundy]

I bet its out of adjustment, so when you're pushing in ton the connector, you're actually making the TPS move to the correct position.

verify the click noise when the throttle moves out of the closed position

[Vincent Brick]

No, that's not it, at least I really don't think so. I tested it with a meter yesterday and it had no problem retaining continuity at the correct position without any downward pressure placed upon it.

[Vincent Brick]

I cleaned the female terminals with a guitar string, and bent the male terminals down slightly, and at first it worked, but within a minute or two went right back to 1400. The female terminals look and feel good, shiny and tight, not loose or corroded, but my buddy who is a tech at a BMW indie shop thinks I need to repin the connector with new pins. He went to far as to suggest a temp fix of a zip tie or baling wire to pull the plug into position long enough to get the car through smog, but it takes a considerable amount of force on the plug to make the connection when it won't just work on its own, and I would much rather find a permanent solution.

Edit: If bending the male pins down doesn't work, then duh I need to bend them up! I did that and so far it has done the trick, but trying not to jinx myself. Just ran some errands and it stayed idling at 1000 the whole time. Will try and take it to the smog place in the morning, 3rd day is a charm, right?