My mechanic thinks I need a new Airflow Sensor/ meter for my 1988 3.2. What to do?
 

My mechanic thinks I need a new Airflow Sensor/ meter for my 1989 3.2. What should I do?

The Car:
1989 3.2 Carrera Coupe.
75,000 miles.
Always stored in winters and taken good care of.


Amongst many other things, CHT and O2 sensors have been changed, as well as flywheel reference sensors and other things that are related here. Fuel and spark are good. DME, plugs, wires, and the control unit, checked out ok.

Here are some symptoms:

Very hard to start. While cranking, it may misfire loudly, cough, and sputter. Sometimes I have to crank it 10-15 times to get it to start.

When it does finally start it runs fine. But, when I get on the accelerator hard, around 6K rpm in any gear, the engine cuts out momentarily. It doesn't turn off, it just cuts off for a second and then continues running. Happens every time at about the same RPM.

What symptoms relate to a bad airflow meter??

Thank you,

RS

Use your Bentley (page 240-16) and a multimeter to verify any anomalies with your air flow meter.

Perhaps the vane in the Volume Air Flow Sensor needs adjustment.

It is a very simple test.

Or, perform a search.

Good luck,

Gerry

Gerry is right. If your mechanic believes your AFM is on the fritz, run the diagnosis on it. There's quite a few threads here dealing with the subject.

I see your a new poster, welcome to the site. Since you're from Chicago, maybe you might want to divulge who did the diagnosis for you. I think there's quite a few people near you who may be able to chime in on whether or not the mechanic is reputable. Just my .02 cents.

DME relay new?

Hello and welcome. If you do a search on here regarding AFM cleaning/adjusting you will find quite a bit of info as well. Sometimes the AFM's can be adjusted/rebuilt. I hope this helps.


Chris

Borrow one from another car to confirm.

Usually I get scared when a mechanic statrs "shotgunning" an issue. That typically tells me he doesn't understand the workings of the system. As others said there is a lot of information out here on how to diagnose and identify a bad component on these Motronic cars.

Ingo

Best idea if you can work that out.

I believe AFMs are NLA as a new part, only rebuilts now, and at $1000-1100, a lot of money if your mechanic is guessing. Plus the quality of the rebuilts is questionable.

If you confirm that the AFM is not repairable and you're looking at replacing it, this MAF system is a no-brainer:

Home

Just installed one and could not be happier with it:

http://forums.pelicanparts.com/porsche-911-technical-forum/450874-new-911-product-pre-announcement-7.html

Hey RS-
Where in the Chicago area are you? Perhaps a few of us in the area can lend a hand on this. Who's the shop that suggested you need an AFM? As others have suggested, the AFM has a propensity to develop grooves in the armature contact area and sometimes a simple adjustment car restore performance. But you might also want to check out the fuel pressure. Perhaps when you shut down the car you're loosing fuel pressure.

+1. If same mechanic changed all the other stuff, has not fixed the problem, and is now suggesting AFM, I suggest you change mechanic instead.

The best idea would be to find a wrench who has a spare AFM to help you out. Otherwise, you might find a local pelican samaritan with a good running Carrera to borrow one from.

Go to this website, and on the left hand side there is a button to take you to the air flow meter (afm) test procedure.

Note: You do NOT have to open up the afm in order to test it. Simply hook up a 9volt battery and proceed to move the vane through it's arc while noting the output on a mulimeter.

Air Flow Meter (AFM) - from "The 944 Motronic DME" by FR Wilk

Curious as to why the AFM is suspect here in the first place. On starting, the idle position switch is telling the ECM to use the idle control valve to meter the air. I'm not sure a bad AFM would make starting so hard. When my AFM went bad it was noticable just off idle and in the lower speed ranges (where the contact arm sweeps most frequently and causes the most wear). It really shouldn't be worn way up at high rpms (high air flow), unless the engine routinely spends most of it's time there?
You do know that 6000 rpm is getting pretty close to the rev limit (6250 for Motronic)? It works by cutting off fuel, so it feels as though you have suddenly lost power.
I'm curious about the hard starting.

Test out the MAF...If not with in normal limits, take it apart and try to do the 944 adjustment in the above thread. My friend took his MAF apart and made the adjustments and it ran fine. If the MAF is bad, what do you have to lose...I mean it is worth a shot to try to break the seal and see what you can do with it, the thing is toast anyways. Play around with it and see what you can do.

Or go big.

AFM to MAF conversion.

See: Home

Hard to start is either a fuel delivery problem or ignition problem. I wouldn't be looking at the AFM yet. Check your throttle adjustment; it might be off. As Dentist90 says, you're possibly hitting the rev limiter early which would also act as if you're pressing the throttle a little on start up (to much fuel?). Change mechanic.

Hard start, backfire doesn't run right....

Very first thing I would do is verify the sparkplug order.
Second check cap and rotor for cracks or traces.
The third if they haven't been replaced would be the timing sensors on the left (drivers side) they get very brittle with age and likely need replaced if they have not been done already. Not a cheap ordeal.

If you find you actually do need an air box. Let me know I have one from a 1984 that was replaced for emmision just before I bought the car and was removed and replaced with PMOs. I would guess however there is another issue.

Only trouble with this solution is the steep price tag just to find out that the MAF was OK, with the same problem still remaining.

Might as well take it to some wrench that makes a living replacing parts at your expense until he finally stumbles on the solution.

Yes his mechanic could be wrong.

And, they are easy enough to fix so this is more in the modification category.

I think you can test them in place with a volt ohm meter by moving the flapper valve by hand.

If it dose not progress smoothly on the ohm's scale, run a 9v batter to it and do the same test.

Thanks for the advice everybody.
 

I'll get another opinion and thank you for the advice everybody.