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

Rose5oh · Jul 27, 2022

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?

KRUISR · Jul 27, 2022

The next day does it behave the same - runs great for 10-20 minutes and then runs like crap?

Rose5oh · Jul 27, 2022

KRUISR said:
The next day does it behave the same - runs great for 10-20 minutes and then runs like crap?

Assuming that i plug the mass air flow back up and go for a normal drive, yes. It runs fine with it unplugged. The car starts up fine and idles fine. Its just after it warms up when it doesnt want to rev

KRUISR · Jul 27, 2022

Okay, now I am confused ...

Rose5oh said:
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?

Rose5oh · Jul 28, 2022

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.

manicmechanic007 · Jul 28, 2022

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

Rose5oh · Jul 28, 2022

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.

Rose5oh · Jul 28, 2022

manicmechanic007 said:
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

Rose5oh · Jul 28, 2022

Rose5oh said:
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

Stock is 19lbs so I think one from the junkyard would make it worse

General karthief · Jul 28, 2022

I wouldn't drive it, it's in 'limp mode'
let us know what codes when you get the reader, also see #7 here http://forums.stangnet.com/showthread.php?t=698148

LX1993 · Jul 28, 2022

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.

Dan02gt · Jul 28, 2022

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.

manicmechanic007 · Jul 28, 2022

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

manicmechanic007 · Jul 28, 2022

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

manicmechanic007 · Jul 28, 2022

If yours is dead you might have to buy another fancy one
I sure would plug another sensor ( or three) into it just for GP's
Watch the voltage on all 3

Mustang5L5 · Jul 28, 2022

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.

Rose5oh · Jul 28, 2022

Okay thanks a lot!

Rose5oh · Jul 29, 2022

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.

Rose5oh · Jul 29, 2022

Rose5oh said:
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.

90sickfox · Aug 1, 2022

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.

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

Rose5oh

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General karthief

wonder how much it would cost to ship you a pair

LX1993

Dan02gt

mazing how much gas smell came from that tiny hole

manicmechanic007

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Mustang5L5

That is…until I whipped out my Bissell

Rose5oh

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90sickfox

Wasn't a pretty sight...and I've got big hands

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

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wonder how much it would cost to ship you a pair

mazing how much gas smell came from that tiny hole

That is…until I whipped out my Bissell

Member

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Member

Wasn't a pretty sight...and I've got big hands

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