EToy

Hey folks. I've got a head scratcher that is likely going to be a pain in the arse to pinpoint. I apologize in advance for the long post, but I want to incite ideas with data, so please stick with me. My 2000 4Runner runs completely fine until the very hottest days, and it's now left me stranded a few times.

It seems like on those extremely hot days (think 90 or hotter) and when either driving hard up and over mountain passes, or driving slow and crawling on forest service roads, the engine gets heat soaked and something starts acting up.

The first thing I notice is the pedal suddenly is completely unresponsive, and the tachometer shows RPMs drop completely down to say 400 RPM, and then bounce back up and start seeking continuously. When this happens all power from the engine just stops, almost like you cut power to the engine completely. Keeping pressure on the throttle will result in the engine suddenly surging and the RPMs going back up as it suddenly regains power. If I stop and let it idle, the RPMs will seek wildly from ~500 - 2K. If I put it in low gear and keep the RPMs pretty high I can usually keep it going, but as soon as I slow down and let the RPMs drop, it will sputter and eventually stall completely. Trying to restart it continues to get harder and harder until it won't turn over, or it won't make enough power to keep RPMs up and just keeps stalling.

I have had this happen while going super slow, crawling, as well as had it completely stall while driving 65 on a really hot highway.

Every time I've had it happen, I let it sit for at least an hour or more and let it cool, and I can usually get down the road for an hour before it seems to get heat soaked again and starts acting up. Most times I've been stranded, I've ended up waiting until evening sets in when it starts cooling off, and then have been able to make it home with zero issues at all. Purrs like a kitten like normal.

It sometimes throws a P0171 (too lean) code when it happens, which leads me to believe it's something with fuel delivery. I haven't been able to get a live scan of data coming from the computer when it's happening, but now have a scanner with me to try to get some insight when it happens again.

Here's what I've tried so far:

• Cleaned MAF sensor with sensor cleaner
• Checked Throttle Position Sensor according to FSM
• Thoroughly cleaned Throttle Body and IAC
• PCV seemed suspect according to FSM details: Replaced

Since it's so hard to reproduce the problem, it's been extremely hard to troubleshoot. I hooked up the OBDII scanner today and took a baseline just to have some data and had two readings coming back that seemed off, but I don't know enough about fuel trims and fuel maps etc. to know if it might indicate anything. See attachment and the values for "Long Term Fuel Trim B3" which is 0, and the "Short term fuel trim B1-S2" which is 100%. Would those indicate something not getting a proper reading/value from a sensor? This snapshot was taken while the vehicle was just sitting idly after it had been run to normal operating temp.

The second photo is the freeze frame from when the P0170 was last triggered when it happened.

I'm going to be criss-crossing the state a lot in the coming weeks for hunting season, and getting stranded (even temporarily) in the desert is disconcerting. Any input and help from the gurus is valued and much appreciated!



OBDII Values sitting at idle after reaching normal operating temp

Freeze frame for OBDII values from last time P0171 was triggered when it was having issues.

moto809

I'm not going to say I know your issue, but over the last few weeks since I completed my 3.4 swap into my 93 I can tell you the P0171 code is about the most useless diagnostic code ever created. The list of things that can cause it is mind boggling.
What you're describing, however, sounds almost like a MAF sensor. When I first got my swap running, I had the MAF sitting loosely in a piece of hose, and if it got out of line at all the throttle would become completely unresponsive until the engine bogged out and died. I don't know if a bad MAF will mimic a misaligned MAF, but it might be worth looking at. It houses the IAT sensor as well, which might explain why it only happens when it's extremely hot.
If you know anyone with a 2000 to 2004 3.4, maybe you can do a quick swap just to check. If I remember right, 96 to 99 MAF is pinned differently, so that would not work.

EToy

Thanks for the reply Moto. Yeah, I initially tried pulling the MAF out of my '97 and doing a quick test swap to the '00, and the engine didn't like that at all. At this point, the MAF is definitely high on the hit list of things to possibly replace. I've cleaned it thoroughly (including the sensor way down there) as a start, but need to run a full battery of FSM diagnostic test to see if anything shows up. The big problem is that it seems to function just fine until everything gets super hot, which is going to be hard to test under those conditions.