My wife's '99 4runner 3.4 has always been kind of hard to start. She's been complaining of pinging and last night she comes home with a CEL. I scanned it and it's a PO171 which is a lean condition.

Trying to do the math to make a good guess where to start first. The first two that come to mind are MAF and fuel pump. Did some searching and the general consensis is it's the MAF sensor. I cleaned the maf about a year or so ago when I did the spark plugs. The fuel filter is not that old. Maybe two years on it.

I know a bad maf can cause pinging and PO171 codes. I don't think they can cause long crank starting though. This leads me to suspect the fuel pump the most.

Does this sound correct?

The Throttle Position Sensor was the cause of my P0171 though I didn't notice any pinging.
Its fairly easy to test with a multimeter though I'd look at the MAF and your vacuum lines 1st.

Check your fuel pressure.

Thanks. That's good advice. First, inspect/clean maf and inspect all vacuum lines. I had not considered the TPS. I can see how that could cause pinging and PO171 if you have the throttle opened a certain amount but the TPS is reporting a lesser amount. The fuel delivery could be less than the required amount.

Also check your EFI fuse, it could be the culprit to a hard start. Yet as 19963 .4 stated, check the pressure first.

Are the 02 sensors original?

Yes, that would be a good thing to do short of just replacing the pump. A quick search says it's not an easy task to check the fuel pressure on these engines. On some cars with high mileage (ours has 180k), it's recommended to replace the pump as preventitive maintenance.

Thanks. I know the post cat sensor is new. Not sure about the pre cat one. I'll check but I was thinking it can't be that because of the pinging. That to me says it's something actually leaning the mixture and not a sensor mis-reporting. Seems to me the sensor is sensing what is actually happening. Does that sound correct?

I cleaned the MAF (turns out it had been 30k miles since I had done it) and cleared the code. I also replaced this EFI fuse. I was surprised how bad it looked when I removed it. Much corrosion and pitting. 4runner seems to be running fine now. Starts up quicker too. Thanks.

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