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Air Flow Meter


lbinh
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I have a 1993 ES300 with 170K miles. My problem is stalling at idle. Car runs very good except at idle. Car has Air Flow Meter and not Mass Air Flow sensor. No engine light or codes.

I first cleaned the IACV valve with intake cleaner and no help. Then, I just replaced the IACV with junkyard one last week (stalling still there) no help. Then, I cleaned the throttle body with intake cleaner, brush and rag. I ran some Seafoam in the brake vacuum hose. Next, I ran an aerosol seafoam intake cleaner thru TB while engine was on. I added seafoam to fuel tank. All still no help. Fuel filter (1yr), spark plugs(1yr), wires(1yr), cap/rotor(1yr), AFM (used junkyard part, installed about 3 years ago), new air intake hose, new air filter have been replaced recently.

I think I can rule out the IACV valve since I just replaced it with a used one. Do you think it might be the used junkyard AFM acting up that is causing the idle stalling? I unplugged the harness and the engine would stall. I replaced the harness and started the car up again and it held idle at 500 rpm. Then, I drove the car and back to stalling at idle it went.

Also, could it be the EGR valve and modulator be causing the idle stalling? Can the engine be running slightly too hot cause the idle issue? The weather is getting hotter here in Houston. Maybe a new thermostat and coolant flush help? I am about to vacuum (my mouth)test the EGR valvle and modulator if I can remove it. I will clean it once it is off. I am really thinking it is the AFM since I played with the harness and it gave some results. Is there any way to test the AFM and could that be causing the stalling at idle? Thanks for your help.

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First things first.

(w/ an assist from Haynes)

Have you tried to increase the idle speed by adjusting the trottle cable?

You may want to replace the fuel filter, again, cheap fix.

Damp or damaged distro components?

Faulty emissions valve (s) (there are like 4 of them on the emissions rail on my '94, this includes checking out the egr,which if stuck open could cause it to stall)

Faulty spark plug cables (what brand did you use last year?)

Vacuum leak -- intake manifold, fuel injectors, vacuum hoses (spray her down w/ wd 40 and see if the stalling stops for a while.

Valve clearances off?

AC idle up failure? (does this happen w/ AC on and off?)

And of course last, pull the plugs and check for abnormal residue, then check the compression (if all else cks out ok).

LL

Not sure air flow meter malfunction would cause stalling at idle.

How can you tell if it hasn't thrown a code? Is the cel actually working?

I'd wonder about compression as well, given it's at 170k mi.

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First things first.

(w/ an assist from Haynes)

Have you tried to increase the idle speed by adjusting the trottle cable?

You may want to replace the fuel filter, again, cheap fix.

Damp or damaged distro components?

Faulty emissions valve (s) (there are like 4 of them on the emissions rail on my '94, this includes checking out the egr,which if stuck open could cause it to stall)

Faulty spark plug cables (what brand did you use last year?)

Vacuum leak -- intake manifold, fuel injectors, vacuum hoses (spray her down w/ wd 40 and see if the stalling stops for a while.

Valve clearances off?

AC idle up failure? (does this happen w/ AC on and off?)

And of course last, pull the plugs and check for abnormal residue, then check the compression (if all else cks out ok).

LL

Not sure air flow meter malfunction would cause stalling at idle.

How can you tell if it hasn't thrown a code? Is the cel actually working?

I'd wonder about compression as well, given it's at 170k mi.

The CEL light works. It goes on then off during ignition. It never stays on. Valve and compression tests are beyond my skills. :wacko: It stalls with AC on or off. Wires (blue colored) and plugs are NGK or Denso I believe. Need to verify that. I will check plugs for residue. Cap and rotor have never been wet. Will check the connections.

I will check EGR items next. If that doesn't work then I will replace the fuel filter again even though the car runs fine at all speeds (even WOT) except when it idles then it stalls.

What does WD-40 actually do when sprayed and does it hurt any rubber or plastics? I will try that after the EGR check. I will check the PCV valve but I doubt that effects idle speed. Also, I read in some posts that adjusting the throttle cable does not do much since the car's ECU controls the idle.

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Spraying wd 40 tends to seal a vacuum leak temporarily. I once soaked the strange gasket inside the idle air control valve in wd 40 and it swelled up to twice its size! A day later it had shrunk back to original.

Your are right, that the ecm does control the idle. So either ecm is getting bad info leading it to reduce idle rpms Inappropriately, leading to stall, OR the ECM can't adjust the idle because the cable is too slack.

Tightening up the throttle cable a few turns, might just work. It's really easy and costs nothing. If it doesn't work, you haven't lost anything, and if it does....

One rule of thumb I always follow when trying to troubleshoot a difficult problem like this is to do things that are cheap and easy first, moving onto harder and more expensive things once the simple stuff has been tried.

LL

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Great tips Lexis,

I am not sure what it gonig on but since the weather has changed to cooler weather or the intake cleaning I performed fixed the idle stalling issue. the car has been normal for 4 days now. Timed coincidentily with the cooler weather. The Seafoam in the intake brake booster, seafoam in gas tank, and aerosol Seafoam intake cleaner thru the throttle bottle while engine was running might of also did the trick. That may have freed sticky valves, restored proper compression, and cleaned the EGR components. I will post later if the problem is fixed or that this wass temporary and the issue returned. Let's see how the car does when weather gets above 90 for a longer period.

:cheers:

Thanks for the great help Lexis.

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  • 3 months later...

I think the extremely hot Texas summer has done a number on my car. The stalling issue has come back and now I have transmission issues.

First, I cleaned the TB, intake, and added Seafoam to the gas and that did not help the stalling like a few months ago. I pulled the CEL DTC codes of 24 and 31. DTC code 24 is the Intake Air Temperature sensor. DTC code 31 is the Airflow meter. Does anyone know where the IAT sensor is? I think it maybe inside the AFM meter also. That would explain why I get both the codes 24 and 31. I will try to install another junkyard AFM meter.

And now the tranny issues. I changed the ATF fluid but issue still there. I can't accelerate from a standstill with any power and when it finally does get up to 20 mph or more then the tranny shifts fine. I pulled the O/D codes of 62 and 63. Code 62 is Solenoid #1 and code 63 is Solenoid #2. Does anyone know exactly where they are and is it easy to replace?

Thanks in advance.

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  • 4 weeks later...

I just gave my 94 sc300 with 50,000 miles to my sister-in-law. She started to have stalling problems recently and it's been fooling everyone. But here's an idea: I sold Mercedes for over 35 years. I sold a friend an older E300 which constantly fired the check engine light. It skunked every MB dealer from NJ to Fla and back. The warranty company finally quit paying the claims when the cost went over $5000.00. It turned out to be the wiring harness. Those old wires get corroded and quit flowing the proper voltage which the ECUs depend on. After hearing about dealers wanting to replace trans, ecus, maf, I have no doubt it's probably in the wiring. Just a thought. I haven't seen anyone even mention it. Look into it.

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