Help! I think my AFM has gone bad

Evil_e34M5 · 15th June 2012, 22:50

Hi guys,
Over the past few months my M5 starting idling really rough on startup. The car would eventually stall out. It would only happen occasionally, on some days it would turn on and idle just fine. Eventually it started happening more and more often. My mechanic had an AFM from an M5 that had been in his shop for years. He let me borrow it and I installed it on my M5. The car ran fine but then the same problem occurred, the idle is really rough then it stalls. The thing is I barely drive this car, maybe twice a month so I don't know for sure that the borrowed AFM cured the problem. This is happening now with two different AFMs. I guess it could be possible that both have gone bad but I was wondering if I could get a little help from any local or even U.S. based M5 owner. See I would love to test my AFM and the one I borrowed from my friend on a M5 that is known to be running well.

My car is a 91 3.6 with 86k on the clock. Recently I did a whole vacuum hose overhaul. The cap, rotor and coil are about 500 miles old. The only other thing I can think of are the ignition wires but if Im going to order the AFM I would like to order everything together. Before I do that I would love to test out my AFM on another M5. Im located in Northern NJ close to NYC. If there is anybody in the tri-state area willing to help me out for 5 minutes I would really appreciate it. If there is nobody around here I'm even willing to ship my AFM to a known board member to test on their M5. Thanks for your time guys.

uk_bm · 15th June 2012, 23:30

When was your HEGO last changed?

Evil_e34M5 · 16th June 2012, 01:02

Quote:

Originally Posted by uk_bm

When was your HEGO last changed?

Yeah I forgot to mention that is on my list of things to change. I don't see any record of it being changed.

uk_bm · 16th June 2012, 08:51

I would also consider a look at the idle control valve, woud have been quite easy to check during your vacuum hose refresh.

Evil_e34M5 · 16th June 2012, 17:48

Quote:

Originally Posted by uk_bm

I would also consider a look at the idle control valve, woud have been quite easy to check during your vacuum hose refresh.

Yup did that as well, brand new unit. I went to the car this morning and turned on in the garage, it idled smoothly... I don't get it. Nothing like the other day, it was completely normal.

Evil_e34M5 · 19th June 2012, 07:03

Ok guys Im pretty sure my issue is solved. Well at least I know what the problem was. Im going to post this in case another board member is having these kind of issues. As I had mentioned before I already had changed the cap, rotor, coil, spark plugs etc etc not even 1000 miles ago so I was pretty sure it wasn't any of those items. Tonight I removed the spark plug wires to check them and I noticed that on plug 1 and 6 there was a little bit of oil on them. Not too much but thats never any good. I cleaned off the plugs and I turned the car on... it was idling and accelerating as smooth as butter. I had turned the car on before cleaning the plugs and it was idling a bit lumpy. I took the car out for a quick spin around the block and everything was great. I also need to mention that I had placed my old AFM in the car while I was doing this.

I'm going to replace the valve cover gasket and decided to go ahead and change the spark plug wires as preventive maintenance. Im very happy it was not the AFM. Dodged a bullet there.