NoHandles13

Hey it's my first time posting I'm currently changing my cAr over from speed density to maf and was just wondering if I'm going to burn my ecu or not. I've been reading controversial things online I bought 89 harness and ecu (auto my cars manuel read worst I'll get is a hanging idel) on eBay because my understanding is it's pretty much a plug and play between 87 88 89 I've switched out the harness so far and just waiting to plug in the ecu till I get a response am I right to think I'm in the clear or is there something else I need to do ?

FourEyed

I've been running nothing but Speed Density for almost twenty years now, never had a problem. Always kept the cars stock though, except for the usual bolt-ons .

delz05

If adding MAF, you will need to use a MAF matched computer, in addition to the wiring and the MAF assembly.

skunk21

Mass air conversion how to was right in our tech info thread:

Look in post #2 https://themustangsource.com/f634/te...os-fox-503775/

90mustangLX

Like above, it's pretty easy to switch over to maf, I've done it before. If everything plugs in the exact same as the SD wiring harness with no leftover plugs you should be good to go. They made a few different wiring harnesses but from my understanding the 89 should be as you said plug and play.

My car is actually still using the a9p computer and I've switched it over to a 5 speed with no issues, the auto computers have more aggressive programming.

skunk21

Yeah the links will give the step by step and needed info. you can use an auto computer with a manual but you cannot use a manual computer with an auto. there are a few "aggressive" ecm codes but once it gets a tune its mute.

NoHandles13

Alright thanks everything's installed and seems to be running great. what a difference in throttle response... The only thing is I find I have a hanging idle when dropping down from high revs sits at around 1600-1800rpm for about two three seconds. I'm wondering if its because of the auto ECM or maybe a vacuum leak.... Any ideas

skunk21

surging idle is a common issue with the fox. it hasn't nothing to do with the "auto" ecm. there are a list of things that can cause it, from a dirty/loose connecting at the 10pin connectors ( salt/pepper shakers is another term, located next to the upper inatke) sometimes using a good electrical parts cleaner or just checking them helps, I dirty/faulty IAC, A TB blade that sticks when returning, bad throttle return springs or needs lube, vacuum leaks. check these things out one by one and see if it helps, start with the 10 pin, the vacuum leaks, etc.