After 150-200 miles, spits and sputters on

Visit the on-line store, know as reliable-store, they have the repair manuals. I'm sure you will get the solution of your problem.
1998 2002 Isuzu Trooper Service Repair Manual INSTANT DOWNLOAD 1998 1999...

which engine, ill toss coin, land on v6
check fuses first.
wont crank? that grrrrr grrrrr grrrrr sound
jumper cable start it yet, why not?
or put in a known good charged car battery?
or using any battery charger charge yours?
or buy a new battery, (if rich)

if it cranks and wont start?
check spark x6 (scan it yet?)
if sparks ok try test fuel!
if test fuel fails 100% see bad belt below.

EVER REPLACE THE CAM BELT?
if not and over 60k on the last one
the belt is doomed, living on borrowed time.
got the V6?

ok what engine is there,? gas or diesel, ill guess, gas.
that symptoms Gob smacks me as, timing errors.
is the cam belt ignore for 6 years. (6x 10k per year, is 60k mile)
that is all part of a tuneup, or doing necessary service on the engine.
the belt slipped,
if you had check spark timing ,it be way off, and that belt caused that.

gen 2, trooper have this line up,
3.2 L 6VD1 SOHC V6
3.2 L 6VD1 DOHC V6
3.5 L 6VE1 DOHC V6
3.0 L 4JX1 TD I4
3.1 L 4JG2 TD I4

i ask every time, and not one ever can figure out whats under the hood. sadly.

the last 2 are diesel...

if you disclose engine that tells the spert, what EFI system is there.

P0401 is EGR problem
P0300 is a cylinder 3 misfire.
Replace EGR valve and do a full tune-up.

Hi

It could be numerous things so please accept this is a partcial solution, just for some idea's for yourself.

Firstly the I would check the EGR valve also known as the exhaust gas recycler valve, this reburns fumes from the engine to improve power and to lower emmisions. very often is the cause. you can clean this with carburetter cleaner and I would recomend you try this before buying another as they are not cheap. What engine isze is this? get back to me and I should be able to tell you the location of the part and how to remove it.

With EGR faults you lose lots of power and the car feels like a lemon, maybe 50 mph tops. its a good indicator if this is how it has been, also lots of black smoke wehn under load.
Hope this helps
Regards
Dan

The throttle body is coated with a sludge resistant material. If you cleaned it all out you are actually hurting your engines performance, because the throttle body resists sludge which in turn protects your throttle plate and bore. You may want to check your egr vacuum regulator, for the cause of your problem.

Close the EGR, check whether still noise is there.
If so EGR regulator has to be replaced

Change the car spark plugs, for sure you solve youre problem. Maintenance, less that $25, for a set of 4 !! God bless !

it may be the problem but if you havent done it already you may want to change the plugs and wires first before buying an expensive egr valve

sounds like it needs a good tune up or mass air flow