Author Topic: missing after up shifting (Read 3368 times)

doitover · « **on:** February 16, 2009, 09:56:51 AM »

I finally have my 91 318is with a Downing Atlanta Supercharger running again. I've only been able to drive it a couple of miles. I deleted the mechanical fan and the electric fan I added wasn't running and I rather not take a risk with it but I did see that it has a problem it had before I started replacing gaskets.

It misses when accelerating after an upshift. Before I assumed this was part of the Idle Control Valve leaking hose issue but I now have a good idle at slightly less than 1000 RPM so that seems to be fixed. There are no engine codes at this point.

Are there any common issues that cause this? It accelerates fine when not pushed and it runs fine at constant speeds or decelerating. It also seems to accelerate OK from a constant speed, it seems to stumble only after letting off the gas for an upshift and then getting back on it.

Thanks for any insight,

xwill112x · « **Reply #1 on:** February 16, 2009, 10:01:20 AM »

air flow meter?

ghoulama · « **Reply #2 on:** February 16, 2009, 12:08:18 PM »

+1.this happened to me after i replaced the icv and related hoses. tested the air flow meter - potentiometer was no good

doitover · « **Reply #3 on:** February 16, 2009, 08:51:12 PM »

AFM is bad. As far as I can tell it was also meant for a six cylinder. No idea if that was intentional.

Looking for a good used unit, preferably in the Raleigh area if anyone has one.

xwill112x · « **Reply #4 on:** February 17, 2009, 08:58:02 AM »

i know a guy in clemmons that has tons of parts...for cheap too.

lemmie know if ur intrested, i'll hook you up with his contact info

doitover · « **Reply #5 on:** March 11, 2009, 07:53:49 PM »

I changed the AFM for one that checks out good for both the pot and air temperature sensor. I also installed the COP kit i picked up a few weeks back. I hate changing two things at once but with my lack of free time I had to do it when I had the chance.

So, success, almost. The car starts well, idles well, runs well except for two things.

It stumbles badly on acceleration when cold. It improves as it warms up. I don't know if it's related but while it idles well, once it warms up the idle is above 1,000 RPM. After starting when cold it idles well at about 800 RPM on the dash tack.

There are no codes. I had checked the resistance on the TPS a while back, it was fine.

Any ideas?