Hey folks. So my 99 3.4 has been pinging when accelerating up inclines in the 20-30mph range, as well as on level ground when accelerating hard (feels hard in the 4runner, not really that hard for your average car) into the 2300rpm range.

I have tried multiple fixes to address both this, and a rough idle/stalling that was plaguing me for a while but has since resolved - fuel filter, spark plugs & wires, cleaned MAF, throttle body, IAC valve. I have tried higher octane gas, fuel injector treatments, did the seafoam treatment.

I had it in the shop this week to get timing belt replaced (157,000 miles, yikes I probably got lucky) and asked my mechanic to drive it around to experience the pinging. His first guess was vacuum hose leak. He told me he did find a small hole which he fixed and claimed he didn't hear the pinging any more when I picked the truck up tonight.

Driving home from the shop I was able to hear pinging in the exact same spots - level ground and on an incline. Called him back and his next suggestion is to have one of his guys who just works on car computers do a computer reset which he claimed can clear up a lot of idle, timing, etc. issues. He charges $90 for that reset.

I have read other threads about possible culprits of pinging - clogged cat, O2 sensor.. Has anyone had their computer reset and had it resolve anything? Just wondering if it's even worth doing before I keep trying other fixes.

Thanks in advance.

Since lately i've been doing a lot of reading, "pinging" from what I've read is due to lack of fuel and too much air - running lean.
Maybe fuel pump isnt supplying enough, injectors or FPR is off. Especially since you specified on an incline when you're asking the motor for "more".

Try and pull the plugs and see how shes burning.

EDIT: I've read even plug gap's being off can cause pinging

What exactly do you mean about the gap being off? Is it a brand thing or a plug by plug thing?

I went with NGK wires and think I did OEM plugs when I replaced them but can't remember exactly.

The anti knock sensor should retard the timing before you can even hear pinging.

Does it sound like marbles in a can?

You can "reset" the ecu by disconnecting the negative cable from the battery for 30 seconds or maybe removing the EFI fuse under the hood.

Also, maybe take the mechanic for a ride to hear the noise.

The gap I'm referring to is the distance between the electrode

I had this problem also. Did everything I could to fix it. Ended up being the MAF sensor. Replaced it with a denso off Rockauto for $75 and hasn't pinged since. Are you getting any trouble codes?

MAF sensor could be my next try. Have never gotten any codes from her. Was yours throwing a code?

Yeah mine was throwing the P0171

So in addition to pinging, now I'm back to the rough idle which I haven't had in about a year. I'm sure most know exactly how this goes but when sitting in gear with the brake on, the rpm needle just bounces then recovers every few seconds, threatening to stall. So I end up keeping one foot on the brake and the other slightly on the gas to keep revs up. Crazy how many things that could cause this and all I've done to fix it. Is it likely or even possible that it could be a bad O2 or MAF sensor when I have never had it throw a check engine light? Just trying to figure out my next attempted remedy that's worth trying.

Are you relying on the light alone, or have you actually checked for codes? Are you 100% sure that the light is working?

Cannot confirm whether the light is working or not. I have seen it before but not in a couple years. But, my mechanic checked for codes last week and he didn't see any.

Turn the key over but don't start the engine. The CEL will be on. If you don't see it, your bulb is out.

My MAF went bad with no CEL. But I did drop it from 4 feet on solid concrete lol.

Try the vacuum leak check - to date this check has found every vacuum leak I've had to diagnose, every time.



If no leak, it's for sure a fuel delivery issue. Main culprits would be MAF (measures amount of air coming in and adjusts fuel), injectors (might be clogged or internals are fried), or the fuel pump itself.