Toyota Repair: Skipping at idle..., toyota tacoma prerunner, clearance problems

Question
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Followup To
Question -
Hi Ted,
I have a 98 Toyota Tacoma Prerunner 4cyl 2.7 Auto 160k miles; it now skips intermitently at
idle: runs smooth for a period of time 3-5+ seconds; then the idle drops off for a split
second -- engine sounds as if it is going to stall; smooth idle returns again and repeats...
Any ideas where I should look for the problem? I changed the plugs and wires about 10k
ago.

Thank You,
Ivan
Answer -
These engines have a tendency to develop valve clearance problems, it could be a tight
valve, have the compression of the engine checked and do a valve adjustment, the valves
will burn and start to leak if they are not adjusted right, another possible problem may be
the idle speed control valve located on the throttle body, it may have to be cleaned.
Is there a check engine light on?

Ted -

Thank you for the feedback: I just cleaned the throttle body, changed the wires (just in case
the others were bad), checked-regapped the plugs, and cleaned the mas sensor. By the way,
you mentioned the 'idle speed control valve', is this part of the throttle body mouth?; I
cleaned the 'butterfly' device device holding it open and placing a rag underneath - using a
toothbrush and reaching in as far as possible, cleaning out everthing afterwards using a
clean rag.   All in all, the problem still persists; I discovered that the "burping" is not specific
to idling.  I raised the rpm's, placing a popcicle stick in the throttle mechanism, to about
1500-2000 rpm's; the intermitent skip-burp can be heard in the exhaust.  In addition, after
cleaning out the throttle body, the truck seemed to have a bit extra power, or at least
seemed the same, now, after driving another thirty miles or so, the truck seems to have lost
power.

Does this indicate your original assumption? -- valve clearance problems (I didn't assume
you could adjust valves on today's modern vehicles).  And if so, and thank you once again
for your patience with this question :), Is it safe to drive the truck for a few more days? -- I
have an appointment to bring it in for service in two days; it might be another day or two
until it actually gets worked on.   

Cheers,
Ivan

Answer
If you can hear the popping noise in the exhaust there is a valve problem, have the compression tested first and if any of the cylinder compression is low try having the valves adjusted, as I said before there may be a tight valve, these engines have a strong tendency to develop this condition, if caught in time, an adjustment is all that is needed, if the valve has been without proper clearance for too long it may have burned already to the point where a cylinder head removal and a valve grind/replacement may be necessary.