2000 4Runner - Shuddering problem

[MattSFO]

I have a 2000 4Runner with 158K miles on it. Been a great truck with little trouble over the last 12+ years. Recently, the truck has developed a shudder. Initially, it was intermittent and confined to low RPM (<1000 RPM) situations usually right after ignition. The problem would go away after a few minutes of driving. I took the truck to the dealer and they could not find anything or reproduce the condition.

Yesterday, however, the problem worsened significantly. While driving at speed the shudder developed and the Check Engine blinked a few times. The problem went away and then reappeared about a half hour later. This time the Check Engine light stayed on continuously for the remaining hour of driving and it blinked a couple times as well.

Today, I drove the care back to San Francisco from Napa. The Check Engine light was lit the entire time, but the truck ran fine. Then, I parked it at home for a few minutes while I unloaded the truck. When I restarted the 4Runner, the light was off.

I am thinking the issue is related to ambient air temperature. The problem has been most severe in hot weather (90 degrees plus) in Sacramento and Napa. It seems to go away when I return to the cooler and damper summer climate of San Francisco.

Given that, I am thinking it could be a sensor problem (maybe mass air flow sensor) vs. an issue with the transmission/torque converter. Any thoughts her would be most appreciated. Thanks!

[Joe W]

I is a plus that the check engine light came on. Now there is a code stored in the computer that most parts stores will hook-up a computer and read the code(s) for free and recommend a fix... as opposed to a trip to the dealer. One can guess about the primary cause but why when the computer can do this for you

[MattSFO]

Thanks Joe. Unfortunately, I took it in today to figure out the error codes and the log history in the computer had been cleared. Not sure why that happened because no one had touched the battery or anything else electrical since the Check Engine light came on over the weekend. So, I am back to Square One.

[jdmccright]

I would check your idle air control (IAC) valve or the engine coolant temp (ECT) sensor. Faulty readings from these can cause hard starting and rough idle.