My 97 4Runner with 3.4l V6 started missing at high speeds when I ran her at 90+ mph one day. I read the forum about the Bosch Platinum spark plugs. I took them out and replaced them with Densos from the dealer. I also changed the Spark Plug wires. They are Bosch also but they were under warranty at AutoZone so I went with them. I measured the coils with an Ohmmeter and all of them were in spec.

Since then, the truck runs fine while cold but once it warms up, it misses when I'm trying to take off. Do you guys think it may be a temp sensor or something?

BTW, this 4Runner has 217,000 miles on it. I just changed the timing belt, water pump, belts, and hoses about 5 months ago. The Alternator is new (rebuilt) also.

Any help is appreciated.

Thanks,

Isiah

 

Check your injectors. Also make sure you dont have a h/g leak or a cracked head

 

Have you looked under the sofa for your missing engine?

 

It also could be a bad coil pack ... your engine should be throwing a code, get it checked and see if the misfires are coming from the same wire/ coil pack

 

i'd suggest checking under the hood first, but the sofa is a good guess too

 

I checked the coils. They measured fine. How should I check the injectors?

 

Haha...You beat me to it.

 

Well, I knew someone was going to do it, so I figured it might as well be me.

 

 

Has the truck ever run correctly after the new parts were added?
If not, I think you can connect the dots.

 

The truck runs a little better with the new parts. It was missing really bad before the change. Now, it's only when it warms up.

My dots won't connect. What should I look at next?

I'm going to Seafoam the engine and clean the injectors in hopes for some results.

 

I would switch out the wires to NGK or OEM as well since you have never gotten the truck to run correctly with the Bosch wires. If you had the timing belt done recently you should probably also have someone check the torque on the crank pulley because if that did come loose then you'd get all sorts of random missing.

 

Oh, your talking about those parts. It has run great since the timing belt, water pump, etc.

It started missing last week and I did the plugs and wires and it didn't go away.

I'll check the torque on the pulley but I'm sure that's not it. It missed before I did the timing belt but stopped shortly after.

 

I think I figured it out. The O2 sensors are in open loop until the truck warms up. That means the ECU isn't looking at the signal. The truck runs fine then. However, once warm, the O2 sensor data is considered by the ECU. Since mine are bad (217,000 miles), that could be the problem.
I also read that the O2 sensors and MAF are ignored by the ECU on Wide Open Throttle. However, if the TPS is bad (mine may be) the ECU doesn't exactly know when WOT is. I may go ahead and replace that too.

 

guessing and throwing parts at a car isnt the right way to fix it. Do some proper diagnosis and figure it out. If you can't diag it then take it to someone who can

 

Why 90mph? Were you just having a lapse in good judgement?

 

90 mph because I had to get somewhere quick.
I've done it before. Didn't think it would make me skip and miss all the way to the market. LOL

Anyways, I've ordered the O2 sensors and the TPS.

 

Alrighty, I replaced both O2 sensors (I was getting poor fuel economy anyway) and I took a stab at the TPS but that didn't fix the problem.

I'm going to take it to the dealer or an independent but I have one last question. Can an ignition coil measure correctly with an ohmeter and still be bad?

 

yep. I have seen coils ohm out ok but they just don't work. If the problem started after you put the new wires on it the first time, I would try putting your old ones, the ones you took off to begin with, and run it again. sometimes those aftermarket wires just can't cut it.

 

X2

The way you check a bad coil pack is by moving it around and see if the misfire code follows.

I hope you've also been following this thread too because much of your diagnosis will be very similar:
https://www.yotatech.com/forums/f2/c...ighway-128206/