[Kind of Solved] Out of Ideas on Why My Car Won't Run Right

[aguyther]

Hey guys, first post which is unfortunately not a positive one. When I bought my '91 318is a few months ago, the buyer explicitly stated that it doesn't run right on startup due to a bad ICV, which is believable, and the AFM needed retuning. When I bought the car it ran great, but on startup for roughly 30 seconds it would idle kind of choppy, and then it would clear up.

Well fast forward a little while later, I was driving home and the car would miss when accelerated or held it at a constant RPM. Due to my ignorance and lack of knowledge on what the ICV does, I ordered a replacement which did not fix the problem. I then took it upon myself to recalibrate the AFM, which kind of helped. But soon after it would start running very poorly again. Surging, missing, check engine light flashing. If I leaned out the car it would idle down and choke, but if I made it rich it would idle very high, and was not getting enough air. Eventually, after tweaking the AFM countless times, and adjusting the idle screw a tad bit, I had it running to where I could daily the car. As a side note, the car has a new starter but has always had a long crank time.

This is where I am at now: The check engine light stays on, though as soon as I hit redline it flashes and car misses. I don't know if it's a misfire, but power cuts out for a split second. When the car is cold, it idles very high for a few minutes, probably around 1.5k rpm, and eventually settles between 900-1,100 rpm. When the car is hot, or is at least slightly warm, it does not like to hot start. It runs choppy like it used to when I first bought the car, except worse and sometimes it will stall out. If I hit the throttle while it is running like that it seems like it's not getting enough air, as the throttle response is basically nill and it revs in a very reluctant and choppy manner. It usually straightens itself out in 30-45 seconds Also, the car seems to not know which readings to go with. I'll do a third gear pull and it'll move like an arthritic dog, and then try another one and it'll scoot right on like crazy puppy.

The stuff that I have checked/replaced: idle control valve, toyed with the AFM (it is now adjusted slightly more rich than it was when I got the car). Checked the coil packs for any signs of being loose, and the plugs did seem to have too much fuel on them, so the car was probably way too rich. I did a very thorough check for vacuum leaks and did not find any.

My possible explanations: Either the AFM is really out of wack or just plain busted. My other guess is that the 02 sensor could've been ruined from the car running so rich. I've also mused over the possibility that the motronics could be damaged, but I don't like to think about that because it scares me. I've read through a few threads of people having similar issues, but nothing nearly as complicated as mine, and after throwing a 150 dollar ICV into the car, I would prefer to figure out what the issue is before I just start replacing parts and hoping that they fix the problem. If you all would like, I can upload a video showing all of the different problems that I explained.

Anyone got any ideas or advice? I'm kind of stuck because I don't know a whole lot about troubleshooting cars; I am confined to doing the basic maintenance, and following online tutorials and write-ups for projects. Diagnosing and troubleshooting is something I have not quite mastered yet.

Edit: I'm going to try unplugging that mystery wire that was noted in one of the sticky's. I'll report back with results.

Double edit: THE MYSTERY WIRE WORKED! Only issue is I still don't have very good throttle response, even after I played with the AFM.

[Tgoode318]

what mystery wire? 

[keflaman]

The black, single wire connector in the wire bundle running along the top of the firewall inside the engine compartment. There was a thread on it recently...like, in the past year. It's a sticky somewhere, but I don't have it off the top of my head.

OP, what are you adjusting on the AFM. I tried that on my former 320i without much success. Cleaning the tracks and looking for breaks is about the extent of what the effort is worth.

Edit: http://www.m42club.com/forum/index.php?topic=7757.0

[DesktopDave]

Kef's link is definitely it. The single wire they're talking about is an additional connection required for some Euro cars. It was unplugged when the car left the factory but it looks like it should be connected. It's just two matched connectors sitting in the wiring loom on the firewall. It's an easy mistake to plug it in if you've made any changes. When the wire is connected it disables the O2 signal input and replaces it with the CO potentiometer from the AFM. It's for non-catalyst cars only. As you can imagine, no US cars will have a correctly adjusted CO pot...I'm not even sure US cars had the proper AFM with that adjuster...so our cars will run very poorly.

@OP: find & eliminate vac leaks first, consider doing the hose delete mod, then check or just replace the O2 sensor, then test your fuel pressure. Did you do a stomp test yet? Not the greatest diagnostic ever, but they can be helpful. I'm betting you'll get a 1221 or 1222; caused by a vac leak in the ICV hose or that rat's nest of intake & heater hoses.

If it's not any of those common problems, feel free to mess with the AFM. I'm no expert, but every time I've played with an AFM it's made the car worse. I'm not saying it's impossible, but these cars don't lean out or richen up based on the AFM/venturi door position like older Bosch CIS/K-Jet/L-Jet systems. Once the car is warmed up and running in closed-loop, Motronic will use the O2 sensor to compensate for any changes to the AFM. Our 1.7 is also an adaptive system and can change fueling parameters on the fly. If the AFM door spring is too loose, those changes will be unpredictable.

[Tgoode318]

Ahh i see, Is this only on e30's?

[DesktopDave]

Ahh i see, Is this only on e30's?

AFAIK

[aguyther]

Kef's link is definitely it. The single wire they're talking about is an additional connection required for some Euro cars. It was unplugged when the car left the factory but it looks like it should be connected. It's just two matched connectors sitting in the wiring loom on the firewall. It's an easy mistake to plug it in if you've made any changes. When the wire is connected it disables the O2 signal input and replaces it with the CO potentiometer from the AFM. It's for non-catalyst cars only. As you can imagine, no US cars will have a correctly adjusted CO pot...I'm not even sure US cars had the proper AFM with that adjuster...so our cars will run very poorly.

@OP: find & eliminate vac leaks first, consider doing the hose delete mod, then check or just replace the O2 sensor, then test your fuel pressure. Did you do a stomp test yet? Not the greatest diagnostic ever, but they can be helpful. I'm betting you'll get a 1221 or 1222; caused by a vac leak in the ICV hose or that rat's nest of intake & heater hoses.

If it's not any of those common problems, feel free to mess with the AFM. I'm no expert, but every time I've played with an AFM it's made the car worse. I'm not saying it's impossible, but these cars don't lean out or richen up based on the AFM/venturi door position like older Bosch CIS/K-Jet/L-Jet systems. Once the car is warmed up and running in closed-loop, Motronic will use the O2 sensor to compensate for any changes to the AFM. Our 1.7 is also an adaptive system and can change fueling parameters on the fly. If the AFM door spring is too loose, those changes will be unpredictable.

Thanks for the response. I'm going to go do a stomp test and check again for vacuum leaks.

Edit: Stomp test didn't work, maybe I have a bad TPS? I'm pretty sure I don't have a 153 ECU seeing as my car is a '91.

Edit 2: So now my issue seems to be isolated to crappy throttle response. When I jab the throttle it hesitates for a split second, and the car doesn't seem to have the same amount of getup and go. It does get better after 2 or 3 pulls. At this point I don't know what to replace. It could be AFM, o2 sensor, TPS, or the FPR. I have already checked for vac leaks and couldn't find any. I also have some random long crank times. Other than that it hot starts perfectly and doesn't idle horribly.