WHAT DIRECTION TO GO? CAR WONT IDLE?

Please turn the caps lock off.


A Speed Density computer cannot be used with Mass Air. You may have some wiring problems if your report of the computer part number or catch code is correct. Fix any computer & Mass Air problems before doing anything else.


MASS air conversion instructions from Mustang Mass Air Conversion | StangNet FREE
A9L (5 Speed) computer from junkyard $100-$150
A9P (Auto or in a pinch, 5 Speed) computer from junkyard $100-$150
70MM MAF from 94-95 Mustang GT - $40-$70
MASS Air wiring harness kit $30-$85

The whole thing is probably less than $300 using junkyard parts.

The conversion harness seems to work well for most folks. It avoids the compatibility problems in using a harness from the junkyard. Simple and cheap, it is actually less work that swapping the wiring harness. I have pulled the stock harness out of a wrecked car and it was like wrestling a big python.

Conversion Harness kits & parts
Interactive Systems & Technologies Mass Air Home Page
Ford Fuel Injection EFI Harness Pigtails

If the idea of moving & soldering wires scares you, here's a list of compatible Mass Air wiring harnesses.

Copied from bbunt302
Just for reference, here's a list of all the compatible years:

89 harness should work for 86-89 as long as you're using mass air.
90 harness will only work in a 90. (B/c of air bags and dual dash connectors)
91 through early 92 harnesses should be compatible (single dash connector, fuel pump relay under driver's seat)
Late 92 through 93 harnesses should be compatible (single dash connector, fuel pump relay under the hood)

Larger MAF to go with Mass Air conversion:
94-95 Mustang GT MAF - $40-$100. It is 70 MM instead of the stock 55 MM on regular stangs built prior to 94. It uses a slip on duct on the side that goes to the throttle body and a 4 bolt flange on the other. You need a flange adapter to fit the stock slip on air ducting that goes to the air box. Wiring plugs right in with no changes. *1 *2

*1.) Metal flange adapter Kurtz Kustomz Motorsports, Inc. KKM Buy the TR70 for $44.95. Or spend some time on eBay looking for one that may fit.
Try AutoZone and ask for 81413 - Spectre / 3 in. Aluminum Intake Mass Air Flow Sensor Adapter at $12.00. You may have to order it online.

*2.) MAF & sensor interchange
The 94-95 Mustang 5.0 MAF & sensor is also found on:
1995-94 Mustang 3.8L F2VF-12B579-A2A,
1994-92 Crown Victoria 4.6L F2VF-12B579-A2A,
1995-94 Mustang, Mustang Cobra 5.0L F2VF-12B579-A2A,
1994-92 Town Car 4.6L F2VF-12B579-A2A,
1994-92 Grand Marquis 4.6L F2VF-12B579-A2A,
Evidently the –A1A, -A2A, AA, etc. on the end of the part number is a minor variant that did not change the operating specs. You should be able to ignore it and have everything work good.

Also see Ford Fuel Injection for help with the harness parts RJM Injection Tech EFI Harness Pigtails:, and connector pins, RJM Injection Tech Ford Terminals:


Computer useage - Copied from Steve89GT

There are a few different varieties of computers... just a few different calibrations.. Here's the #'s of most of the MAF computers that are around. A9L and A9P are the most common.

1988 MANUAL 8LD
1988 AUTO 8LF
1989 MANUAL A9L, A9S
1989 AUTO A9P, A9T
1990-92 MANUAL A9L
1990-92 AUTO A9P
1993 MANUAL A3M
1993 AUTO C3W
1993 COBRA X3Z

A9L - 89-93 5.0L Mustang 5-spd
A3M - 93 5.0L Mustang 5-spd
A3M1 - 93 5.0L Mustang 5-spd
X3Z - 93 5.0L Cobra 5-spd
A9P - 89-93 5.0L Mustang Auto
A9S - 88-93 5.0L Mustang California
C3W - 89-93 5.0L Mustang Auto
DA1 - 87 5.0L Mustang 5-spd
J4J1 - 94-95 5.0L SVT Cobra 5-spd
T4M0 - 94-95 5.0L GT Vert 5-spd
U4P0 - 94-95 5.0L GT Auto
W4H0 - 94-95 5.0L GT
ZA0 - 95 Cobra R
D9S - Lincoln LSC
ZXA3
LLX3
CCA1
CCA0
AOL2
AOL3



Fix any computer & Mass Air problems before doing anything else.

See the "Surging Idle Checklist for help with all your idle/stall problems. Everything you need to find and fix idle problems is in there.

The first two posts contain all the updates to the fixes. At last count there were 24 possible causes and fixes for surging idle/stall problems. I continue to update it as more people post fixes or ask questions.