MAF Sensor Question

Hey everyone, thanks for the add! On my 1998 Tacoma I bought a couple weeks ago I lost throttle response when driving. It's idling rough and when you press the gas pedal it barely moves the RPMs then drops back down to idle RPMs. It does change the RPMs in neutral though. It will also move about 5 mph but that's just from idle RPMs.

I tried cleaning the MAF with MAF cleaner but no luck. It was dirty though. I'm considering replacing it but did read in this forum that it's best to use OEM. What is the part number for the denso oem MAF sensor for a 1998 with a 2.4 engine? Also does anyone have a wiring diagram I can use to check the current MAF sensor with my meter? If you guys have any other ideas on what else to check too I would greatly appreciate it.

 

Is there any particular reason you suspect the MAF or did you just randomly pick a part?

 

The symptoms seem to match the symptoms of a bad MAF sensor. I wanted to verify it with my meter but didn't see the procedure or wiring diagram on how to test it. I'm a commercial HVAC Tech so I'm familiar with troubleshooting, I would always rather test then be a parts changer. Just have to learn a little more about this truck and how to test the parts.

 

Based on those symptoms are there other more likely things to be wrong? Do you know the procedure for properly checking the MAF sensor? I would really appreciate the help from someone who knows these trucks better, I'm really not sure at this point what the problem is

 

I'm no expert in MAF problems.

The 96 repair manual gives a test. I'm not sure it's different for 98. Back probe 2 of the terminals (VG & E3) with a voltmeter, turn ignition on, blow air into the MAF and see that the voltage fluctuates. Thus doesn't sound like a very conclusive test.

There seems to be a lot of discussuon of MAF problems, so search around. I wonder if checking the live data with a scanner shows anything in particular for a failing MAF, like fuel trims that are way off.

 

Did they have CEL and codes in 1998? Wouldn't a MAF problem throw a code?

 

Yes they do have the OBII System

OP just what code or codes are you getting ??

Gotta Have at least a code reader

 

It had a code that said need to replace thermostat before it did this. Since it isn't moving over a crawl I haven't taken it to check for new codes. Is there one you recommend to buy? I'll try searching the forum today

 

It can be one of many things but start with getting the codes read cause we are all just stabbing in the dark with guesses. If you unplug the MAF it will go into limp mode but should run better than how you describe it's running if the MAF is bad. This will throw a code for the MAF as well but should run rich and stable-ish.

 

I had a 1998 Extra Cab with 22RE. I also found the "O" ring was bad that seals the idle speed screw. Photo attached. You can get a new O ring at Ace Hardware.

 

code PO171 was MAF for me in a '96 3RZ. Went through a few other things like the fuel filter, but when I replaced MAF, everything went right again. It wasn't nearly as bad of a condition as the OP described- mine was just a stumble off-idle at intersections.

 

30k maintainence routine

 

Well I plugged the code reader in and it said no power train DTCs are present. I didn't even look at the CEL when it came on because I assumed the thermostat would still have it on. After that I unplugged the MAF sensor and started it up. It showed the DTCs for the MAF sensor and ran better. Plugged it back in and now it's running normally again. At first after taking it out it had some poor acceleration/hesistation but it was actually accelerating. After about 5 minutes it was back to running normally again. No check engine light and I double checked with the scanner. Still no DTCs after I reset the MAF code. The last two times I tried it after it started doing this it didn't run right. I'm not sure if it's an intermittent problem or if unplugging the MAF did something

 

I would still clean the MAF with MAF Cleaner and disconnect the - battery cable for 10 min.

 

I cleaned the sensor this weekend but never disconnected the battery. Is that required for it to start reading properly?

 

It just resets the ECU so it will relearn how to run with a clean MAF, and it should clear any codes

 

Does disconnecting and reattaching the MAF do the same thing?

 

There is a way to test the maf with a volt meter, by backprobing a couple wires. Basically it should be at a steady voltage at idle then smoothly increase as you give it more throttle. Don’t remember exact volt maybe 0.5 at idle then increase to 4-5v with rpm. As long as it’s not jumping around volt wise it should be good.

 

No