Why does manifold get hot while running on

running to rich

clogged cat.

Timing Problem

That will ruin the exhaust converter
& oxygen sensors also

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.

When you get in running, check you fuel pump pressure, also check for the proper operation of the fuel pressure regulator.

While you're at it.....hook up a vacuum gauge to a manifold vacuum source and see what kind of reading you get.

Fast idle could possibly be a intake leak. Probably should expect to get a normal reading of between 15 & 20 inches of manifold vacuum.

First of all you have to check emissions, if you have smoke of some sort being emitted then it suggests an incomplete combustion is taking place.
To solve this first you would need to install an ignition booster ( ~250$)
and about the idling its normal for 4age to idle around 2k rpm but If you want to control the idling speed then you can tighten the screw just at the T.V.I.S (intake manifold) at the top right hand side of the unit.
To get better idle speeds you may want to run synthetic engine oil instead of mineral oil due to the viscosity remaining somewhat same (at room and hot temperatures) with synthetic oils.
finally have your A.F.M (Air Flow Meter) or M.A.P(Manifold Absolute Pressure) sensor checked and then finally get the computer tuned at a dyno facility through your mechanic and for the computer to be programmed for higher fuel efficiency.
If you want to go further however have copper spark plugs installed.
Cheers.
I own an AE92 FXGT. Its a sweet ride however mine is the 1988 corolla.

Aside from having a faulty fast idle valve, you may have a leaking intake manifold gasket.

try the throttle position sensor

your fast idle problem might be caused by your coolant temperature sensor not getting a good flow of hot coolant. The sensor is mounted up on top of your throttle body. Here's a test: after you have just made a trip, put your fingers on the area where the coolant temperature sensor is. It should be very hot, but I suspect yours will be only lukewarm. Unless that sensor gets hot, your computer will stay in the "warmup" mode forever. Your idle speed will not be controllable, your fuel mileage will be poor and your engine will run a little hotter than normal. The coolant flow needs the throttle body to pass fluid freely and also your interior heater core is part of that flow, so that can't be obstructed either. The coolant flow ports are very narrow and sometimes they get a piece of gasket sealer caught in the throttle body. Get some air and blow it out. Good Luck, friend.

Check for a intake manifold leak, we had some problems with seals used on the upper section of the intake on your engine, get a can of carb spray and spray it around the intake, see if the engine reacts, if it does you have a leak.