Engine Car idles fine, but will not rev with MAF plugged in. HELP!?

Rose5oh

Member
Jul 27, 2022
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4
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Macon, GA
Hello. I have a 93 mustang, 5 speed. Just built a fresh motor 306 with TFS stage 1 top end kit, 24lb injectors with 24lb MAF meter and an A9L ECU with no modifications. The motor runs great and car drives great, and it hasn't been tuned. After driving it for maybe 10-20 mins, the car slows down as if I'm running out of gas, meaning I'm pressing the throttle but I'm not getting any response. So basically the car won't even rev but it will idle. So I finally come to a complete stop and I decided to unplug my MAF meter to see what happens and the car revs and drives just fine. I drove it back home and parked the car because I'm not sure what the issue would be. Has anyone else had an issue similar to this?
 
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Okay, now I am confused ...

Assuming that i plug the mass air flow back up and go for a normal drive, yes. It runs fine with it unplugged.

Is the mass air plugged in or not?

Have you pulled the codes and see what you have? Have you tried disconnecting the battery to reset the computer? Does it change anything?
 
no the maf is not currently plugged In because it won’t let me accelerate or drive the car after it’s at operating temp, unless I unplug it. So now I just leave it unplugged. And yes I’ve disconnected the battery Several times.
 
Well, at some point you are going to have to plug the maf back in
Get three from the junkyard
Can you read the maf pid?
Had a similar problem with my 04 heritage truck
3 mafs later and mine would run fine but idle around 2 grand
Mine ran great with the maf unplugged. It just had the light and would not pass I/M
Back in your day some of the maf sensor connectors were faulty
You interrogate yours
Heat shrink tubing and solder if you have to replace it
Good luck
 
Also I have checked the TPS. I haven’t pulled any codes but I just ordered an OBD1 code reader so soon I will find out what codes are being thrown. I’m pretty sure i should not be driving the car with the maf unplugged so I’m trying to see if there’s anyone that has had a similar problem.
 
Well, at some point you are going to have to plug the maf back in
Get three from the junkyard
Can you read the maf pid?
Had a similar problem with my 04 heritage truck
3 mafs later and mine would run fine but idle around 2 grand
Mine ran great with the maf unplugged. It just had the light and would not pass I/M
Back in your day some of the maf sensor connectors were faulty
You interrogate yours
Heat shrink tubing and solder if you have to replace it
Good luck
No I don’t have a way to read it currently. And this isn’t the stock mass air flow meter I have. It’s a New Pro-M 24lb from Anderson Ford Motorsport
 
Need to run codes. Runs in open loop until it warms up. Refers to predetermined tables. It will also stay in open loop if a sensor input is lost. So unplugging the maf forces it to run in open loop. Should go to closed loop (refering to air/fuel mixture) when warmed up. Likely codes are for maf &/or O2 sensors, (correct input required for proper closed loop operation). Hell, another likely cause is a vacuum leak. If the maf is an issue, send it back to Pro-M, they will repair it at no charge. Ultimately you will need a tune. It will never be 100% without one. Trouble is finding someone who can properly do this. If they don't have alot of experience with foxbody's and OBD-1 stuff, you'll be wasting your money. Cheapest option is a chip, I'd get ahold of Willie @ "DirtyDirtyRacing". Further mods will require another tune however. Best option is a standalone such as MegaSquirt, Holley, etc.
 
Unplugging the MAF meter puts the car in limp mode and fueling calculations are coming from pre-defined tables at that point. So there could be a number of things that are the problem and unplugging the MAF is masking them. Things that come to mind are:

MAF of course (there have been some flaky aftermarket ones)
ECT sensor
ACT sensor
TPS
O2 sensors
TFI overheating (but this normally causes the car to outright die or miss)

The surging idle checklist on this site shows you how to test all those. You should also try to pull codes when it starts acting up, but before unplugging the MAF.
 
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Well it's the sensor on the top that your processor is dealing with
The size is no matter?
Not real up on the not stock stuff as we saw very few modified ones back in the day
Worst case scenario we would be dealing with the light on constantly but the cars ran fine with superchargers and big mafs
I deal with pids so much around here with I/M and cars running chitty
I have bought 3 scan tools for my friends that read pids for around 40 bucks each from effing china
You should get one
This way when they call me I can ask them what the scan tool said
Makes my life easier
 
DanO is right
Rash of codes sometimes if you unplug your maf
You can backprobe the maf voltage, on some of them without a scan tool (it's hard on the connector)
Looking for about 1.3 volts at idle and 4.5 at 3/4 throttle
I think yours is dead Rose5oh
 
I’d dump the codes with the MAF plugged in. KOEO and KOER before the problem and after the problem occurs.

I’m suspecting the MAF here. If you have your 19s and stock MAF still, you can try swapping them in just to see if the vehicle actually runs.
 
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How’s it going guys. My scanner came in today and I just wanted to give you all an update with what the numbers mean also. It did confirm that my mass air flow is indeed an issue.
 

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Did you hook the engine coolant sensor back up after all the work. It's located in the coolant pipe that runs along on top of the intake ? There's also an intake temp sensor that's installed in the intake on the drivers side. I've seen people mix up these sensors and the connector ( sometimes ) will go on either one but they are different.
 
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