Air Flow Meter Help

[pslynam 1]

Hello all,

 

So following on from my previous thread my 1.6 GTi is now starting fine. However with the air flow meter plugged in, the car will not rev above 2,000 rpm and misfires when idling and revving. If you boot the throttle it will just die. If you blip the throttle quickly a few times you might get the revs to build up to about 4,000 rpm.

 

However with the afm unplugged the car revs perfectly and the misfire seems to be gone although it runs very rich with the afm unplugged. So is this a simple case of a bad afm and just fit a replacement? Or could something else in the fuel injection system be causing this behaviour? I did notice when the afm was plugged in, the car was idling quite fast (1,500 rpm) and never settled down even when warm as though the SAD was not working properly?

 

Cheers for any suggestions.

[j_turnell 137 3 Cars]

Sounds like the flap in the air flow meter is stuck open, pull the air pipes off and check.

[Tom Fenton 1,542]

I reckon it could be another fault, normally an 8v won't run at all with no air flow meter. That's yours will run with the air flow meter not connected I reckon means the mixture is far too rich due to some other fault. I'd look at the coolant temp sensor first.

[pslynam 1]

The flap in the afm isnt stuck as I checked this before. Will have a look at the coolant temp sensor.

[2-Pugs 57]

Check you haven't got an air leak between the arm and the cylinder head. I had terrible running problems once and it turned out to be the bolt that holds the oil filler funnel was missing, letting in unmetered air and making the mixture richer

[toolie72 67 1 Cars]

My car won't start with afm disconnected, I've done that by accident after cleaning it out, if ecu doesn't have any returns at all how is it going know what to do

One of us must have an issue

Got anybody nearby you can compare/beg/borrow/steal/brain pick-I'd put out an SOS topic with your area marked-might even make a friend lol

[pslynam 1]

Had the car running today with afm unplugged, runs very rich when it is not plugged in. When I plug the afm inn the revs immediately rise and it does't seem to run as rich any more.

 

Does this look like the afm is working ok and coolant temp sensor is dodgy?

[pslynam 1]

Hi all,

 

Still having problems with my car's running. Have replaced the coolant temp sensor and got a replacement AFM but this has not resolved the issue. So with the AFM unplugged the car will idle and rev but is running very rich.

 

With the old AFM plugged in it would not rev, would just start misfiring and die when you press the throttle, as though it was being flooded. When the car is running and the new AFM is plugged in the revs immediately rise (like it is trying to compensate for over fuelling??) and then the engine just dies after a second or two.

 

So I'm wondering where to go next, could this be an ECU fault? Or a throttle switch fault?

[Anthony 1,003]

For testing purposes you can just unplug the throttle switch completely - it will run fine without it plugged in, you'll just lose the fuel cut on over-run and WOT enrichment.

 

As Tom said earlier, something seems very odd as usually it won't start/run without the AFM plugged in.

[j_turnell 137 3 Cars]

Have you checked the ecu temp and afm wires making sure all pins are making contact and no wires are broken? Was the car being used daily before this or have you just got it going?

[pslynam 1]

The car has been lying idle for a number of years and off the road until I purchased it before Christmas. Will have a look at the wiring and clean up the contacts.

[j_turnell 137 3 Cars]

Not sure what else you've done but worth changing plugs, leads, dizzy cap, rotor arm etc and fresh fuel if you've not already.

[Telf 224 2 Cars]

I'm sure it shouldn't run with the AFM disconnected - mine wont. This would point to a wiring issue surely?

[pslynam 1]

I noticed yesterday the electrical connection to the SAD was unplugged. Does this connection carry a signal to the ecu to add more fuel when the car is cold? I plugged it in but made no difference, maybe the SAD is bad, car still runs but runs rich when AFM is unplugged

[welshpug 1,661]

the ecu has no connection to the sad, its just a 12v feed to it, you'll just have an elevated idle when warm with it unplugged, or rather an idle that doesnt drop from cold idle speed.

[pslynam 1]

I thought the sad opened and closed mechanically via a metallic strip hence Im not sure why there would be a live feed to it?

[welshpug 1,661]

there's an electric heater element in it.

[pslynam 1]

Ah ok. So how does the ecu know to inject extra fuel when the enginee is cold and the sad is supplying air to the inlet manifold? Does it use the reading from the coolant temp sensor?

[welshpug 1,661]

yes, and the position of the afm flap.

[mhyphenl 10 1 Cars]

Hijack!! Does anyone have any advice on re-setting a tampered with AFM? By tampered I mean the spring being adjusted?

[pslynam 1]

Turns out after much investigation and some professional help this issue was caused by a failed vacuum advance unit and a poorly adjusted throttle body. All seems well now.