Firstfives.org

My '81 528i has had this issue for the past couple of years. I have noticed that it has gotten worse since I got the car in 2007. The previous owner drove it regularly, I drive it every few weeks, or at least let it run for a while.

Since I drive it infrequently, I like to let it warm up in neutral for a few minutes before I hit the road. I notice that about 5 minutes after I crank it, the idle will start to drop to under 500 RPMs and almost stall, but pick back up. It will do this consistently until I start driving it. Once I am driving it for a few minutes, it stabilizes at a steady 1100-1200 RPMs.

I have seen a lot of people with similar issues, but not similar fixes. My motor has less than 70k on it, but I assume all the accessories are original (153k). I started with the cheapest possible fix, which was the cold start valve. It seems to crank a lot better, but it still has the idle issue.

What should I look at next? Aux air valve? Idle stabilizer valve? AFM?

My interior has been at the shop for the better part of a year and I am about to get it all back... I am looking forward to enjoying some quality miles in the car and figure now is a good time to sort this nagging issue out.

Thanks!

I have somewhat the same problems with my 78' with 165,000. I've been thinking of the AFM as well.

My guess would be the Aux Air Valve.
Clean it like you would the ICV on an E28.


I'm sure Mike W. or Lenny D. will check in and give you the real solution, until then...
Good luck and please report back with your progress.

x2 on the AAV, first.

Second, read my rather biting post on the other warmup component here

Thanks guys. Sorry Lenny, so much info on what it could be... you never know! I'll check all the stuff out.

Sherman, do you have a spare AAV off a parts car? PM inbound.

This one I don't have a good answer on, my guess would be the AAV, followed by FPR or FI temp sensor. Possibly the AFM, but I would doubt it.

Assuming I cleaned the AAV right, that's not the problem.

If my car has the newer style thermostat housing with the "A" stamped on it, do I need to order newer style sensors or the sensors for the '81 5er (not sure if there is even a difference).

JoshInAtlanta wrote:Assuming I cleaned the AAV right, that's not the problem.

Not necessarly. If it's tired and not opening far enough it would idle too slow while cold.

If my car has the newer style thermostat housing with the "A" stamped on it, do I need to order newer style sensors or the sensors for the '81 5er (not sure if there is even a difference).

As long as it screws into the hole, the correct one for the 81, but I think they may all be the same within a long run. You could also try adjusting the screw in the bottom of the AFM, screw it in to get it richer, but I think it's a lack of air, not fuel.

And remember, I'm making educated guesses, nothing more...

Mike,

Thanks for the suggestions. After I posted, I went back down to the garage and removed the AAV again. I loosened the adjustment nut, jammed it mostly open, and then tightened it back again so that I could guarantee it would be at least half open.

It's idling a little higher, but still dropping intermittently just as it was before.

I agree with you that it is air instead of fuel. I am going to order a new coolant temp sensor, and probably go ahead and replace the AAV since it doesn't seem to be moving freely much anymore.

Did you clean up your ground connections back there by the AAV as Lenny D. suggested?

swatterssr wrote:Did you clean up your ground connections back there by the AAV as Lenny D. suggested?

Yeah, huh? Didja <it's really important>

Inquiring minds want to know...

BTW, you can check the values of the coolant temp. sensor at its source before you pony up for a new one. They are:

70 degree F (of the water, i.e., cold) - 1950 to 3000 ohms
100 (warm) - 950 to 1600 ohms
160 (hot) - 250 to 550 ohms

Excuse my rant.....

It had been a long week and I had been doing pure city driving in Seattle and car was acting up....of course when I left and went out to the Olympic Penninsula and down the 101, if was Purr-fect.......and, I fell back in love with my ride. Got 25 mph too! Whoo-Hoo!!

Anyways, would any of you know if I have grounds up by my AAV in my 78'? I've cleaned it and such, and it's better, but I have no adjustment thing and it's hard to get a good look up in around there.

It's running pretty good, and not having such the problems Josh is.

Mine now seems to start up at a low rpm, 1100 or 1200, then to 1500, then to 1700, then back down to 1000 and it purrs.

I think I have some senors to change. And, good luck to you Josh.

cpalmer wrote:Excuse my rant.....

It had been a long week and I had been doing pure city driving in Seattle and car was acting up....of course when I left and went out to the Olympic Penninsula and down the 101, if was Purr-fect.......and, I fell back in love with my ride. Got 25 mph too! Whoo-Hoo!!

Anyways, would any of you know if I have grounds up by my AAV in my 78'? I've cleaned it and such, and it's better, but I have no adjustment thing and it's hard to get a good look up in around there.

It's running pretty good, and not having such the problems Josh is.

Mine now seems to start up at a low rpm, 1100 or 1200, then to 1500, then to 1700, then back down to 1000 and it purrs.

I think I have some senors to change. And, good luck to you Josh.

On the '78 you're AAV is under the rib cage, intake manifold, not mounted on the valve cover.

The ground that we're referring to is in the same place on both year models,
or at least it is on my '79.
The AAV was relocated on the '80 + models.
This ground is located on a tab that connects to the the intake manifold
and points downward towards the valve cover.
It is aft of the throttle housing just before you get to the rear of the engine.
On mine, it's two wires connected to one ring terminal.

And getting 25 mph isn't anything to Whoo-Hoo about.
25 mpg, now, that's a Whoo-Hooer!!

Messed around with the ground yesterday. It's pretty good.

Time to mess with the sensor and maybe the AAV again.

In my most polite voice:

I've posted this elsewhere (too) many times but look at the wires peeking out of the crimp on the connector back by the AAV, on the manifold. If you can see them , look to see if they are shiny or dull and oxidized. If they are (dull), plan to replace the connector, by cutting the old one from the wires, take the two (three?) wires and cut back to fresh shiny wire. SOLDER the wires to a new terminal. Permanent end to ground problems realted to coolant temp. sensor (that governs warmup enrichment) and ECU.