Van idles ok, but when I raise rpm to around 1500 it starts surging real fast. Ant ideas

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.

Cars are design to run at a higher idle at start up to warm them up quick. There is a sensor that reads water temperature and tells your car's computer how fast to idle. Your RPMs seem slightly high but not out of the norm. Does idle ever drop to around 600/800 after about a minute? If not, your engine temperature sensor maybe defective.

fast idle speed screw, works off the fast idle cam which the choke adjustment sets, it works together by linkages. This is the raised idle speed setting you need to keep a cold engine running. First you set the idle speed by the idle speed screw with engine at normal operating temperature. Then you set the linkage up so the cam is on a raised step, throttle will be held on that raised step. then you can turn the idle speed screw to get idle at about 1500-1800 rpm. Now when you start engine cold, choke will set the fast idle cam on that raised step- when engine starts and runs it should be running at your fast idle setting. That's how it supposed to work, you just have to get everything adjusted right. I hate carburetors, they never stay adjusted right. Considering their complexity and small mechanical parts, no wonder.

surge, great post, what engine displacement.
open hood (my answers are USA only) look up, see big white
sticker that is the engine vacuum and type engine sticker)
surge hot or cold? engine.
if it surges hot, that means :
1: ISC system out of control , it job is to stop surge and 5 more things.
2: the engine is way lean and cause ISC to loose control

just 2 reasons, and can be 50 things. wrong.
is the CEL lamp out running> if not, pull the DTC codes and post them. (all)
as a mech ,we find out which it is.
(i make sure my engine can hold closed loop at idle , if not and lean it will surge. (may)
we make sure the ISC works ok (not sticking, clean it)
and then test to see , that if by my forcing it closed, by hand (ask)
i can get way below 800 RPM. most do 500 but 600 is ok.
if rpm stays above 800 closed, that means you have huge
vacuum leak or TV blackage (too thight throttle cable?)

finding vacuum leaks can be horrific, task .
there are many tricks (and tests) to do this, ask.

see that logic above, If I the mech, can not drop rpm below 800
by hand, then no ISC on earth can. not now or ever.
and proves the induction has huge air leaks
or some dolt set the spark timing 20 degrees advanced.
see it.
so as always , a tuneup is first, then as always , i always check timing,and for proper advance rates.
advances engines at idle race way too fast and the iSC will just go NUTS.

ISC = Idle speed controller , that valve that has wires.
the IAC is a thermal device and no wires and it too can stick open
when the IAC sticks open the ISC goes , yes, nuts,
nuts can be surge (ECU is hunting it)
or just racing way too fast hot, say 1500 rpm.
a slow RPm can be a stuck open EGR (50k service point)
lean will cause too low.
too rich , misfires and too low
the ISC is the last thing to work right, all else must be good.

what does your CEL lamp do?

PS: most cars, if the ECU/PCM enters Limphome, it cuts all idle controls. again, the CEL lamp. glowing while running.../????

I'm assuming the truck runs ok once it is warmed up. Sounds like you need to make some adjustments. The cold idle speed is set too high, and the choke is opening too fast. The cold idle should be around 1500 rpm and the choke should take at least 90 seconds to open depending on air temp.

I would suspect the IAC (idle air control valve) first. Probably has a lot of carbon build up. Hope I helped, TJ

Look for a vacuum leak (lines and intake), Is the engine light on, were any codes present? A faulty EGR or IAC could cause the problem too. Check the throttle cable for any restrictions.

Certainly sounds like the o2 sensors have become contaminated and are not acting as fast as they used to , or are supposed to.

Check your EGR or your Idle control Valve. This can cause a problem with your irratic idling