Aftermarket air flow meter

[Musikmann]

The dealer couldn't get, or decided it was too expensive, to install a genuine Toyota AFM. They bought one from Advance Auto and installed it. My idle is now rough and erratic. I found some used AFM on car-part.com, one was as low as $25 off a '89 Camry. Should I take a chance on that, or a newer one available from a '91 to see if the symptoms improve? Or should I complain to the dealer? I don't think this aftermarket part is that good a unit.

[91 Camry]

bring it back to the dealer since they did the work.

[Musikmann]

Thanks, that's the way I'm leaning too. I fully realize I'm paying too much for dealer labor and parts for a 21 year old car, but at least I have a warranty on the work.

[Doctor J]

I could speculate that this dumb dealer does not know about AFM idle mixture adjustment screw (located under the round 10mm plug) on the AFM. The screw under the plug changes X-section of the bypass channel to limit amount for the air going around the meter.
On early 79 Supras this screw was not sealed at all to allow periodic idle mixture adjustments.
Later the mixture control was sealed to prevent tampering, however if new meter is installed, the initial adjustment must be done (and then the plug is installed)

[Musikmann]

Thanks too Doctor J. But one of the reasons I use these guys is because of the shop foreman (right under the service manager/co-owner). He was with Toyota in some other capacity when my car was new and knows his way around with a wrench. I spoke with him right after the job but that was before I noticed the idle was off. I'm going to make another appointment using that as my chief complaint and we'll see where that goes.

Do you have any idea who the manufacturer is for an AFM being sold by Advance auto? And is there any reason to believe that this part is some cheapo offshore substitute?

[Musikmann]

Took the car to the dealer and the shop foreman came out to take a look. As bad luck might have it the car was idling fine for him. He checked the relevant vacuum lines and said there was no idle adjustment on this car. I asked about the idle air mixture adjustment and he didn't comment. What he did recommend was that I check the coolant level when cold in the morning because there might be an air pocket in play saying that could cause an erratic idle. I didn't quite follow his logic.

I didn't mention it earlier but they found an unrepairable leak in the hose/pipe and the bottom of the rad. and that was replaced during the same service visit so the coolant was r/r.

I'll do what he suggested in the morning but today, and when warm, the overflow resevoir level was perfectly within normal limits. He wants me to check the level in the actual radiator and if it is not up to the neck, to top it off with tap water. I have some distilled and that's what I'll use if necessary.

[Doctor J]

The foreman must refresh his knowledge by looking at
http://www.autoshop101.com/forms/h34.pdf
Page 4, Figure 2.42.
If rough idle is suspected and no codes are present the tailpipe measurements using 4 gas machine should be carried out or the “fuel trim voltage” should be measured at diagnostic connector and must be steady around 2.5V (0V means rich mixture, 5V means lean mixture).
If mixture is normal (0.1…0.2 % CO) but engine runs rough (and shows 100 + PPM of HC and/or elevated O2) levels suspect the mechanical problems
The shop should also carry power balance test to rule out minor head gasket or valve leak.
If mixture is lean (CO 0.05 and less) check the hose between the AFM and plenum for vacuum leaks (in addition, the leaks are common after old hoses of ¼ inch ID are removed and placed back on its fittings; they will have cracks after that such as hoses for PCV system)
Other cause for rough idle on V-6 is faulty EGR valve).
Back in 1994, when I was working in the shop, we measured the distance from the top of the mixture screw well to the screw itself on the old (original AFM using dept gage of the caliper and set the screw the same way on the replacement AFM, before mounting it on the car; after that we fine tune the mixture screw after the engine reached its normal operation temperature and sealed the well with the plug.
Too bad I am not working as automotive service technical support consultant, but I should qualify for that (I have BSET and MA degrees but the job requirements for such position are stupid

[Musikmann]

Doctor J, thanks for your additional information. I think I'll print this and show it to the shop guy. I haven't checked the radiator flujid level yet but the car is still idling better than it was just after the new AFM was installed.

[Doctor J]

The computer may learned new settings and adjusted mixture accordingly(but fuel trim voltage may be shifted).
I saw the 96 Mazda Protege with huge crack in the flexible hose between AFM and throttle body; the computer corrected the mixture (car runned ok) but set the code.
Changing the hose ($75 back in 2005)) fixed the problem

[Musikmann]

Idle was still inconsistant and I stopped by the Toyota dealer. The shop foreman worked me right in and at least this time I could demonstrate that the idle was rough to one of the techs. The 2 of them looked under the hood and drove it into the shop.

Their solution was to adjust the throttle intake. The foreman told me to expect the idle RPM to be higher and to watch it for a couple of days. Then he asked about what fuel I was using. I told him Shell 93 octane and he said Kroger's (local grocery chain that sells fuel) owns Shell, which I think is unlikely, but they evidently have some sort of marketing agreement. Anyway, he said they have seen several Toyotas that were refueled at the Kroger's near them and said to avoid them. OK, so I will use Exxon next time.

I drove it for about 30 miles at highway speeds, mostly to run out the tank of possibly "bad fuel" and the idle at warm seemed better after the run. I will see how it behaves tomorrow.

But the kicker is they charged me about $30 to fix what they might have screwed up in the first place. Forman said "I have to pay the tech for his time and that throttle intake adjustment was not easy".

Hell, what happened to dealer warranty work? I'm paying the extra money so I have recourse. This whole scenario is making me mad.

[Doctor J]

I am so sorry, but I never run across the term "throttle intake adjustment " when working on 2nd gen Camry.
The throttle body has an idle speed adjustment (which changes the RPM but not the mixture); throttle stop screw (which should not being touched) and throttle position sensor which is adjustable but will set a code 51 if idle circuit is open with throttle released. Again, if this adjustment is messed up the engine will die at acceleration or deceleration, but usually will idle normal.
I the first thing to do before touching any adjustmenty screw is to read the fuel trim value (+ on Vf, - on E1, instrument set at 10 VDC scale, engine at idle warmed up; reading should be steady between 0 and 5 volts, 2.5V target).
Many people working in the dealership are lacking elementary automotive literacy!

[Musikmann]

Well I hope they didn't mess with the throttle stop screw but I'm afraid they might have. He said something like "that's the one we never touch".

So far a fresh tank of Exxon seems to have made no difference. But I stopped by an Advance (where the AFM was sourced) where I know the manager. He took a long look and his best guess is my symptoms are ignition related and he would do a tune up. Further he said that my spark plug wires are the factory originals and I am at 72,000 miles on the plugs. He said do the distributor and rotor at the same time.

Does this sound reasonable?

[white90dx]

Originally Posted by Musikmann

Well I hope they didn't mess with the throttle stop screw but I'm afraid they might have. He said something like "that's the one we never touch".

So far a fresh tank of Exxon seems to have made no difference. But I stopped by an Advance (where the AFM was sourced) where I know the manager. He took a long look and his best guess is my symptoms are ignition related and he would do a tune up. Further he said that my spark plug wires are the factory originals and I am at 72,000 miles on the plugs. He said do the distributor and rotor at the same time.

Does this sound reasonable?

Wow, yeah. The complete ignition system (minus coil) should be replaced about every 60k miles. So you'll want new plugs, wires, cap and rotor. NGK for the plugs, OEM for the rest.

What made you suspect the AFM in the first place?

-Charlie

[Musikmann]

Sorry but I overlooked this: the hose between the AFM and throttle body was cracked and they replaced that when they swapped the meters.

[Musikmann]

Hi Charlie,

And thanks for the input.

The AFM was the dealers dignosis. I had a guy check the air filter for me and while doing that he ripped the wires out and, as far as the dealer was concerned, destroyed the damn thing.

As soon as I can find the money I'll have the tune up done.