What causes manifold on a car to get red hot

The idle is completely computer controlled, it is not adjustable.

well gee, there are 50 reasons.
did you scan the PCM yet, if not ,why not?
when the idle surges, that means.
NO RPM ranges stated, if super low rpm check EGR.

1: engine lean and ISC dead, or cant handle the huge engine power drop..The PCM can even make this worse!, buy hunting the ISC to find spec, idle and failing... to...
2: or any of 50 other things causing huge engine power drop and PCM can't maintain idle controls.
super lean burn.(bogging)
super rich burn, misfire for 50 reasons.

i cant hear your engine,nor feel it, or see it shake from gross misfiring.
no can i drive it and see/feel power loss,
can I?
asking net bunny's this (blind as bats)
is "OVER THE TOP" no?
so here , ill toss the dice for you
and guess gross misfiring.
ever get a tuneup this decade, if not bingo , no?

and the others...

http://jeepdied.com/Misfire101.html

link even has the 50 cause list, to show the futility of guessing!
we do 1 to 10 tests. and find it.
for sure.

as you can see EFI systems are complex.
gue$$ is not only expensive but can net you 2 problems easy.

Sounds like possible MAF sensor or Positive crankcase breather valve may be dirty or blocked , have known a dirty air filter to cause similar effect also .

Your cat is clogged and backing up pressure causing your manifold to get hot,will crack.

running to rich

clogged cat.

you seem to be snatching at straws. that is ok. many do.
panic sets in.... its a machine and all fail.
You have dangerous high idle speeds, this is dangerous.
why not seek help. any mech can find this, Any!

The car has EFI , and idle controls.
A/Cs sets faster idle , by about 200 rpm ,
800 hot , to 1000 hot (in general)
The car has an idle speed controller that is failing.
there are other ways for this to happen, all complex.
1: intake manifold air leaks.
2: some dork, spun the distributor guessing at timing, fire him.
3: ISC bad. (or IAC) electric idle or thermo idle controls
4: throttle linkage jammed. (cruise, throttle or A/T kickdown)
5: or Toyota disease, the floor mats are hitting the throttle (dumb)
there are more..
it takes tools to fix cars, and know how. do you have tools?
that includes gauges.
guessing is expensive.
ask any mechanic to look, its not costly for just a look.

this car EFI, or CARB, ill toss COIN, EFI gas.
what 4 cylinder, name it there are 7 used.
I'll now toss my coin land on GAS 4 cylinder engine. (in usa?)
is it racing too fast hot
or RPM too low hot.?

we cant guess what your statement above means.
but
the exhaust manifold cracks will cause the 02 oxy sensors to LIE,
to go lean (0volts ) this cause the fuel injection
to go RICH, (cause and effect closed loop rules)
and can idle too slow. (see that word SLOW)
the wrong word you used, after reading this vast times.

"NOT idle at very low rpms"
i decode this to mean?
NOt idle at proper low RPM (800 hot)
or spec 800 rpm , is more clear
that means the idle races hot.
this word is in all books on cars. engine RACES




IF true RACES it's not :
the exhaust crack, but can be if engine EFI slams in to limphome mode, do the flash codes show 12?
you never did those did you , bad idea skipping that. Google isuzu diagnostic jumper and read.
it's not he fuel tank ever,. not RACING.

what can cause any map based engine to race
well frankly LOTS:


but can be reduced to: (physics +)
1: throttle cables jammed. no slack. bad.
2: throttle valve jammed (gunk below it does that)(in the throttle body)
3: all vacuum leaks, (put huge list here, ask)
4: ISC or ICA valves stuck open
5: engine not reaching and holding 180f will cause #4 above to fail, naturally. bad thermostat. cause.
6: someone hacked your TB. (ask)
TB = throttle body.

vacuum leaks is an all day wall of text post
i refuse. but do have links to them.

If the cat is cherry red as you say it is I would check the firing order or timing they may have crossed plug wires this will cause the exhaust manifolds to get red hot and glow let me know if this heled you and good luck.It definitely sound to be timing related or crossed wires.

The most common cause of this is a air pocket in the cooling system, If you've done a coolant flush, changed a hose, radiator, etc..Im not saying that every honda that has a surging idle has this problem but I've worked at a honda dealership for over 10 years and I see this quite often. Let the car idle with the cap off for a while and if that still doesnt do it, jacking up the car as high as you can on the left side while its idling works too..theres a 25 tool thats basically just a funnel that stops this problem if you do alot of your own mechanical work.