strudel

I bought a used maf and installed it on my '86 3.2 w/ssi's and sport muffler. I have 2 problems. 1. The idle surges when cold, about 200-300 rpm. It goes away after a few minutes. 2. When the throttle returns to the idle stop (engine warm and been driving for awhile) it surges 100-200 rpm at 1000 rpm. The idle stabilizes after a minute or so. My mechanic says the the injection signal from the Autothority chip turns on and off when the throttle is returned to a stop. The closed throttle signal is o.k. I'm not getting much help from Autothority. Anyone else experiencing this. Any cures?

Lorenfb

Try and isolate the problem by first disconnecting the O2 sensor.
Next, make sure that the idle switch on the throttle body is closed
when the throttle linkage is at idle. After this, replace the chip with
the stock chip. Also, you might check the fuel pressure, about 38psi.

Good Luck
Loren
'88 3.2

Lorenfb

Additional Note:

If you have as noted a MAF (mass air flow sensor) which replaced
the AFM (air flow meter), then your problem may be the MAF. I don't
have much regard for those units especially a used one.

Good Luck
Loren
'88 3.2

strudel

Loren,
the stock AFM works fine. Not sure if the problem is with the maf unit or chip. Will try a stock chip and see what happens. Thanks.

Lorenfb

I think the MAF unit requires a special chip (different from the AFM performance
chip). Hopefully your performance chip was setup for the MAF.

Good Luck
Loren
'88 3.2

strudel

The MAF does require a special chip, which came with the unit. I figured if I tried another chip I could see if the on/off surging went away. Hopefuly I can determine whether it's the chip or the unit.

Fahrvergnuugen

I don't mean to hijack the thread, but what is to be gained by replacing the AFM with an MAF?

strudel

After I installed the SSI's and a sport muffler I had a few mechanics stated by adding the MAF I would get a faster throttle response and a better idle. When I did the Jerry Woods rebuild class a few years ago someone asked how much more h.p. you would gain with a MAF. Bruce Anderson said 5-7 h.p. with this improvement alone. I noticed the faster throttle response and it seems a little peppier. Since I've been having surging problems with the MAF I've been switching back and forth between the Autothority MAF w/their chip and the stock AFM w/a Steve Wong chip. I bought the MAF used. I'm sending the MAF chip to Autothority to check and see if the surging problem is related to the chip or something else.

Lorenfb

I really doubt about the 5-7 HP. Think about it:

HP = torque x RPMs

torque = energy from fuel charge x mechanicals of the engine

AFM and the AMS can basically supply the same amount of fuel if setup right
based on the optimum AFR of 12.6. Yes, it's possible that the AMS has a little
better throttle response, but we're talking about HP. Also, the key reason
for the OEMs using the AMS is the overall better fuel metering, i.e. better
emissions and economy. The AMS is a lot less reliable than the AFM as can
be seen by the replacements on the 996.

Have Fun
Loren
'88 3.2

strudel

I can't attest to the 5-7 h.p. claim. Only a dyno might prove that. I thought it was a more reasonable number than the 20-25 h.p. claims I see.

MikeF

Strudel,

Hold everything. You're getting lots of bad advice. Autothority is useless to boot...ask me how I know.

Now...it's been a while since I set up my MAF but...there is a very small potentiometer on the wiring harness that controlls the AF ratio at idle. It's about 6" from the MAF itself. When I installed mine it did the exact same thing. Turning the pot clockwise makes it richer, counter clockwise...leaner. When it is cold and the idle is erratic, start turning the pot clockwise....it will take several turns. I believe it can turn like 20 complete revolutions or more. As you turn it, the idle will begin to stabilize. Once it does, leave it there. I'm guessing it's too lean at idle. The pot doesn't do anything above idle, so it will not effect the performance of the car otherwise. Play with it to achieve the desired result.

Trust me, your Autothority chip is fine.

strudel

Mike,
I set the potentiometer per Autothority (2200 ohms) and confirmed it on an analyzer then played with it. The problem is the injection signal from the chip (?) turns on & off when the throttle is returned to the idle position. The rpm surges 100-200 rpm at 1000 rpm for a while then settles down to 1000 rpm. The closed throttle signal is o.k. It's too annoying for me to live with. Autothority agreed to check out the chip, we'll see what happens.

Chris Picklo

A friend of mine dyno'd a before and after with an MAF - if I remember correctly it was 16 bhp.

Steve W

Strudel, like Mike said, you're getting lots of bad and useless advice. That whole system is relatively simple. Before I'd send the chip in for a checkup, check the MAF element itself. It is most likely coated with oil drawn in from the K&N filter which will cause the car to run leaner than it should overall. This is what 90% of the problems with those MAF meters are, if it isn't for the potentiometer Mike mentioned. Using an appropriate hex wrench, remove the four sensor element screws to remove the sensor, and use some brake cleaner and a gentle Qtip to clean off the tiny wire elements. Reinsert, and don't overoil the air filter. Then proceed as Mike recommends, making sure that the tiny wires used to connect the pot to the harness have not broken off already. You'll want to set it at idle at normal running temps to where the exhaust measures the same, with the O2 sensor connected or disconnected. You can use the voltage off your O2 sensor to verify this. Good luck.

MikeF

Strudel:

Sounds like you've got a handle on things but.....don't rely on the 2.2k ohm setting. I ended up having to set mine at about 5.9k ohm to achieve a stable idle. With it set low, it was very erratic, cycling up and down repeatedly. It would make an audible "sucking" sound as it cycled. If this describes what you're experiencing, give it a try.