90 sidekick idle

[diesel (Glenn)]

My wife has a 1990 sidekick 1.6 8v that does the usual fast idle when cold then idles down and starts to surge from 800 up to 1500 and will do this all day no matter how hot it gets.

[Bex]

Welcome to the forum!
First, confirm that your check engine light is on with the key on, and then off once the car starts. And exactly what your car does from cold start - your car should rev to about 2000 rpm, then within 5-10 seconds, drop 500 rpm to about 1500 rpm, then slowly drop down to 800 rpm warm steady idle. You need to confirm that your car actually heats up to proper running temp (do you have great heat in the car??) Basically what is happening with your car is that the ECU is hunting. It always tries to regulate so that you have the proper air/fuel ratio, but if you have any vacuum (air) leaks, - any vacuum hoses that are leaking, any components that are not seated properly that allow more air in, etc., the idle will go high, then the ECU tries to drop the idle to proper rpm, and is unable to keep it there, due to the vacuum leaks, etc., so the idle keeps surging.
You can first start by pinching your vacuum hoses with a pliers - you should not get any reduction in idle in any hose, but if you do, this means that you have an air leak on that component/hose.

[xxx]

x2
surge is 1 of 2 things
1: motor is lean, and eCU cant raise idle due to gross lean. (ecu opens ISC motor fails to speed up) {or ECU drops ISC and motor fails to slow down ."ENOUGH !!"
2: or ISC failure. (on 8v vacuum leaks)

ISC failure is not bad ISC, its a system, in which all parts work together,

what i do is add propane GAS running , if the surge stops, it was lean.
if not, ISC failure.


my bad idle page covers all 3 generations
see that here.
the 89s is the most hard to fix. (old, + can't unplug isc + no isc air hose , pain)

I got a bad idle , cold or hot engine!

as with all EFI.
does the coolant get to 180F and hold , ? real degrees, not guessing?
the ECU goes nuts, below 158F (it sticks in cold start mode. like drive a carb car with the choke on , all day)
that us first check. besides the obligatory, CEL on key on, CEL off running, (posted, 10,000 times, now)


BTW , the 89 ISC can hunt, that is , if it loses control of idle, it will hunt, to find 800 rpm HOT.
it can only do 2 things, give up. or hunt for 800.. its just a software servo

what i do is kill the iSC, and see if i can get 400-500 RPM ,
if not, you have a big leak.
one common leak is the mid TB body center gasket cracking and sucking in and causing, IAC leaks. (ports in side TB ) age related.
and many more air leaks. (huge list on my page and step by step tests to find EVERY ONE)


the first 89 I say hunt was the DP stuck open, hot, ( DP extracted after 30 seconds hot start)
this is classic 89 failure.

does your DP retract? that is the first step ,(after hot test)

does this device retract?

test 1: does it?
http://www.fixkick.com/IDLE-AIR/Dash-pot.html

[diesel (Glenn)]

Well it was a hole in the small vac line by the cowl the hose is about 1.5 inches long.
We thank you very much wife is now off my back.

[Bex]

Yes, part of the functions of this forum is marriage counselling, and we are glad that we have returned another couple back to their wedded bliss!!! Glad that you got it sorted.

[xxx]

vac line by the cowl (fire wall has the MAP)

the line from H3LL, the MAP, the most important hose on any kick.
x10 the bad effects. too..

car is old, and hose dont really last that long, not at all....