Unstable idle - Air Flow Meter problem?

[SouthSwedeSpider]

I've had my car for 4 years now and still I haven't been able to get it to idle smoothly. I have to keep the idle RPM at around 1000-1100 to get a reliable idling, but still it has a tendency to misfire about every 4-5 seconds. When driving, there is a slight tendency to misfiring/sputtering when driving at low rpms, say 1500-2000, but it's not really a great problem. Acceleration and driving is fine otherwise, it pulls strong and always starts without problem.

I've checked the following so far:

• All vacuum hoses - appears OK

• Cam timing - OK

• Cylinder head, valves etc - OK

• Distributor, rotor, ignition cables - OK

So I started to look at the AFM to see if the problem could be lying there. At a closer look, the AFM seems to have been opened and re-sealed with silicone, see pic below. Also, the air bypass allen bolt is literally screwed up and there is no way to turn it by any conventional tool:





When I removed the big air intake hose, the AFM looked like this inside, is this OK?



I have really no idea of what it should look like, but my belief was that the flap should be closed when the engine is not running. The flap is freely movable by hand, so it's not stuck. Could this be from where my problem is coming, that a PO has tampered with the AFM? And what should I do with the allen bolt, are there replacements available? Any ideas or input are appreciated.

For the record, I haven't checked ignition timing yet, so that could also be a potential source. BTW, any ideas on how to best loosen the distributor locknut are also welcome, I just can't get to it with any of my wrenches.

[rlux4]

As well as can be seen by your picture, the interior of the AFM looks OK. They do need occasional cleaning to eliminate gunk build up which would eventually cause interference with the movement of the flap. You should be OK with that air bypass screw unusable, the other one on the throttle body should be adequate for setting up proper idle. If your ignition timing is off it can definetely cause poor idling. Make sure it's set for 10° BTDC which is factory spec., you can fine tune it "by ear" after you've got it tuned well. Another thing to check is the condition of the resistor track of the AFM, Take the black cover off and look for a bad spot on the black resistor track. Could be a bad spot that's getting rested on at normal idle. The sweep arm can be moved up or down the shaft to create a new path in the resistor track. This tutorial is for Porsche, but it's also a L-Jetronic, so it will be the same repair;
http://the944.com/afm.htm
Ron

[majicwrench]

That is not an idle speed adjustment on the AFM, that is a mix adjustment. I would cut a groove in it with a dremel and then use a standard screwdriver.
Keith

[2ndwind]

That is actually the cap. Remove it and you will find the allen head mix adjustment screw well below it.

[So Cal Mark]

correct-that is a seal from the factory to prevent tampering. Drill a hole in it, insert a screw to remove it and you'll find the allen below. The mixture screw on the AFM is completely different than the air screw on the throttle body. The throttle body screw won't affect mixture, it merely raises or lowers idle speed

[grittracing]

mine seems to drive fine. But idle at 1800 and than every 5 th or 6 th stop drop to nothing and stall. And it is running real rich. Could this be the same problem? I know nothing about FI if it where a carb i would already be dialed in in and running great.

[SouthSwedeSpider]

Thanks for pointing out that it was just a cap, not the allen head Anyhow I don't think there will be any chance that the mix will affect my idling problem, I merely saw it as an indicator that someone had tried to fiddle with the AFM. I'll give it a try this afternoon.

[2ndwind]

I had an idle problem and found both the big intake hose had a crack underneath AND the idle screw o-ring was worn and sloppy, allowing air in.

[MikeR]

BTW, any ideas on how to best loosen the distributor locknut are also welcome, I just can't get to it with any of my wrenches.

I use a combination of two tools i) 'crows-foot' wrench with a square drive socket attachment and ii) a short 'stubby' wrench, 17mm

[htchevyii]

I replaced the nut on mile with a 12mm reduced hex nut. Now I can use a much smaller and easy to maneuver wrench.

[whiterabbit]

+1 for the crows foot wrench on an extention! It was the only way I could tighten mine. Worked great for the frt shock towers too!

[Razooli]

All the crows-foot wrenches I had were too thick.
I found a 17mm distributor wrench online for Ford 2.3L engines (VIM Durstan Specialty Tools V111 ~$15). I rebent so it would fit into the limited area we have and thinned out the box so it would fit over the nut.

[124JOE]

ive been using just a 17mm stubby for 14years

[timinator]

I've checked the following so far:

All vacuum hoses - appears OK
Cam timing - OK
Cylinder head, valves etc - OK
Distributor, rotor, ignition cables - OK

I'm curious how you checked these items to determine they are ok? A vacuum gauge is a valuable tool to use with idle quality problems. The engine vacuum at idle will tell you a lot about where to look for your problem. If the amf has been tampered with it would seem that it would have been adjusted to the best idle which that adjustment could produce. It is always best to leave the expensive and complicated parts alone until all the other possibilities have been well explored. Good luck, Tim