1990 2.6 idle problem

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1990 2.6 idle problem

Postby 90turbo1 » Wed Jun 25, 2008 11:30 am

so I just got the newest trooper of mine running and it runs very well

except for this

when you start it it idles about 900 rpm to 1000. (on dash tach)

then you go drive a bit and when you come to stop sign and push clutch in the idle will hang around 2k and sometimes bounce up and down a bit and settle at about 1500 rpm it continues to run great. if you blip throttle it will return to normal.

valves are adjusted properly (intake .008 exh .009) cap rotor wires plugs great condition. no leaks, all new vacuum lines.

thanks
1988 trooper II, 2.6L 5 sp
1991 Trooper II, 2.8L 5 sp swaped to a 3.4 at liest I can drive it now!!! but far from finished
1997 Rodeo, 3.2L 5 sp. Waiting on title :roll:

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Postby isuzufool » Wed Jun 25, 2008 11:36 am

First thing to check is that the throttle plate is closing all the way like it's supposed to. I have had mine stick periodically and cause similar issues. I have even added a helper spring to get one of the plates to close fully. The little linkages on these throttle bodies leave something to be desired after they get old! But oil it a bit and see if you can't add a spring to the upper valve plate like I had to.
'89 pickup, 2.6L with .040 over pistons, MUA5 tranny, calmini header, custom air intake, 2.5" exhaust, 3" lift, stock axles, 33" regal trailblazers, aussie lockers, 217k miles and counting, 80k on engine
'88 Trooper II LS, 2.6L automatic (still a work in progress)
'05 F-150 crew cab 5.4L V-8 with custom exhaust and SCT Livewire tuner/monitor :-)
'00 Rodeo LS, 3.2L automatic

CV shafts are made for breaking, right?
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Postby mattfromtelevision » Wed Jun 25, 2008 11:53 am

My '89 does this, but only under these circumstances. I start it cold, drive approx 10 minutes, and when approaching a stop sign, put in the clutch, and slow down, the Troop gives 4-5 rpm pulses, then stops and never happens again until the next time i start it from cold.

I've been going back and forth between Coolant temperature sensor and IAC. I think I can hear my IAC spinning, like I could in my old Talon, that had obvious idle issues.
'89 Trooper LS 2.6 5sp
32"x11.50"
3" Lift
Aussie locked front
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Postby 90turbo1 » Wed Jun 25, 2008 2:34 pm

THANKS, i was going to clean the tb and lube it today, also the spring is a good idea.

where is the iac located
1988 trooper II, 2.6L 5 sp
1991 Trooper II, 2.8L 5 sp swaped to a 3.4 at liest I can drive it now!!! but far from finished
1997 Rodeo, 3.2L 5 sp. Waiting on title :roll:

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Postby ZuCruTrooper2 » Wed Jun 25, 2008 2:54 pm

Well Matt, I can save you a little headache--the 2.6 does not have an idle air control valve.

Clean and lube the throttle body and replace the throttle cable. Mine used to do that every time I stopped until I replaced the cable. Once in awhile when it's super freaky hot, it'll do it occasionally.
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Postby isuzufool » Wed Jun 25, 2008 5:17 pm

JOHN, what do you mean it does not have one? I know it does not have one like most newer vehicles, but it does have that iac valve that is supposed to be fully open at cold start and then slowly close on a timed interval as the engine warms up. You know, the one under the intake manifold.
'89 pickup, 2.6L with .040 over pistons, MUA5 tranny, calmini header, custom air intake, 2.5" exhaust, 3" lift, stock axles, 33" regal trailblazers, aussie lockers, 217k miles and counting, 80k on engine
'88 Trooper II LS, 2.6L automatic (still a work in progress)
'05 F-150 crew cab 5.4L V-8 with custom exhaust and SCT Livewire tuner/monitor :-)
'00 Rodeo LS, 3.2L automatic

CV shafts are made for breaking, right?
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Postby m-79_grenadier » Wed Jun 25, 2008 6:07 pm

isuzufool wrote:JOHN, what do you mean it does not have one? I know it does not have one like most newer vehicles, but it does have that iac valve that is supposed to be fully open at cold start and then slowly close on a timed interval as the engine warms up. You know, the one under the intake manifold.


I think what you are talking about isuzufool would be the auxiliary air regulator or AIR for short. 8)

Some of these use collant lines to determine the time of opening but the 2.6s is controlled by the ECM. A faulty one of these (if the little clock spring goes out) can cause hard starts, and high idles. It is possible to readjust these but Ive never done it before. Theres a little bolt with red sealant on the underside that winds the clock spring on the little flapper valve to determine when it should open. Im sure you could readjust it but getting it to poen at the right time with the temp of the engine is the trick. Ill check my factory manual and see. 8)

The IAC valve on the 2.6l is a manual adjust screw on the throttle body. Unlike the TBI systems where this scerw is electronically controlled by the ECM and plays a major part in the operation of the motor, the IAC in the 2.6l works similar to a regular mixture screw on a carburetor. Only that instead of the mixture being changed like in a carb the whole amount of incoming air is changed to adjust the idle speed. In the TBI systems the screw is electronically controlled and adjusted by a servo, determining the idle speed of the motor from the ECM.
-Vince
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Postby isuzufool » Wed Jun 25, 2008 10:18 pm

YEAH! That's what I was trying to say! :lol: I did know that these engines don't have an iac like most newer engines (of any make).
'89 pickup, 2.6L with .040 over pistons, MUA5 tranny, calmini header, custom air intake, 2.5" exhaust, 3" lift, stock axles, 33" regal trailblazers, aussie lockers, 217k miles and counting, 80k on engine
'88 Trooper II LS, 2.6L automatic (still a work in progress)
'05 F-150 crew cab 5.4L V-8 with custom exhaust and SCT Livewire tuner/monitor :-)
'00 Rodeo LS, 3.2L automatic

CV shafts are made for breaking, right?
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Postby Kearney » Wed Jun 25, 2008 11:34 pm

I've been having this problem too for a long time.
'89 Amigo 2.6 XS 4WD 5 spd 221k
'01 Audi A4 2.8 AWD Quattro auto 85k
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Postby 90turbo1 » Thu Jun 26, 2008 11:45 am

removed and cleaned tb and installed a new base gasket, checked hoses and all fittings, none are leaking. reassembled, now it will hang around 1500. adjusted idle back down to 900rpm and it will stil creep up. must be passing air past the adjuster, I will remove it and change orings on that tonite
1988 trooper II, 2.6L 5 sp
1991 Trooper II, 2.8L 5 sp swaped to a 3.4 at liest I can drive it now!!! but far from finished
1997 Rodeo, 3.2L 5 sp. Waiting on title :roll:

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Postby ZuCruTrooper2 » Thu Jun 26, 2008 1:57 pm

Check the hoses on the a/c idle bypass solenoid. Switch their positions real quick and see if that helps any. They could be on backwards very easily and they are position dependent.
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Postby 90turbo1 » Wed Jul 02, 2008 5:04 pm

there is no ac fitted to this trooper, would it still have that solenoid??

and where would It be located??

thanks
1988 trooper II, 2.6L 5 sp
1991 Trooper II, 2.8L 5 sp swaped to a 3.4 at liest I can drive it now!!! but far from finished
1997 Rodeo, 3.2L 5 sp. Waiting on title :roll:

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Re: 1990 2.6 idle problem

Postby TroopDawg » Sun May 02, 2021 1:36 am

This post has really confused me and what i think i know about my trooper. I have a 91 2.6 itech with Nd mua5.. it has an IACV (idle air control valve) located under the intake. It plums in between the intake and the throttle body. It is fully open when cold and closed when hot. It almost acts like a chocke. It is controled by the ecm. It will fluxuate a little flap valve to regulate air as it warms up and as you drive. It also has a red screw in it but ive never adjusted it or know how to.
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Re: 1990 2.6 idle problem

Postby giusedtobe » Mon May 03, 2021 4:15 pm

TroopDawg wrote:This post has really confused me and what i think i know about my trooper. I have a 91 2.6 itech with Nd mua5.. it has an IACV (idle air control valve) located under the intake. It plums in between the intake and the throttle body. It is fully open when cold and closed when hot. It almost acts like a chocke. It is controled by the ecm. It will fluxuate a little flap valve to regulate air as it warms up and as you drive. It also has a red screw in it but ive never adjusted it or know how to.


Troop this is an old thread and they are confusing Gen 1 trooper engines with later Isuzu engines. (maybe 2.6 but who knows) Either way I think the IACV either works or it doesn't. There is a video on youtube by john showing how to test these. If you can remove it (I know its a bear) the test is easy to do. Now there might be a a point where the hole might be too big when warmed up and I couldn't tell what that might be but IMO they work or they don't. Mine has some odd idling behavior on occasion that usually causes me to over adjust the idle screw. I think what it really boils down to is vacuum leaks in the intake or elsewhere for high idling. As for the slow idling, mine's done that too. I think the old TB is guilty of some of this stuff. So far it has not been enough of a trouble for me to the point to try to fix it. Only thing I did to the TB in rebuild was clean it as good as possible without tearing it down.

Regards,
Alan

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Re: 1990 2.6 idle problem

Postby DSUZU » Mon May 03, 2021 4:29 pm

Again, this thing is getting spread around like Corona. It is and will confuse folks.
FWIW: The IAC / compensator (the one UNDER the manifold) starts out open (cold) and slowly closes as it's INTERNAL heater warms the spring (just like an electrical choke). It is NOT powered through the ECM.
There is also a fast idle valve that is (usually) located on the right fender. It is controlled by the ECM and A/C controls. Dennis
1991 LS Trooper 2.8 V6 5 speed conversion (Sold)
1989 LS Spacecab 2.6 5 speed 4x4 manual hubs, Rodeo torsion bars, extended shackles, 2" lift, K&N air filter (drop in), dump bed conversion, burgundy interior change, warn brush bar. Engine is bored .020 oversize and upgraded to 1994 pistons, head and EFI system.
Previously owned: 1987 Trooper II LS, 1989 Trooper (parts only), 1994 Trooper 3.2 Auto, 1997 Rodeo 2.6 5 speed, 1993 shortbed pickup 2.3 (project - sold) 1992 Rodeo 4x4 LS (parts car, devoured by Spacecab needs) plus some 70 plus other non Isuzu vehicles over the years. 1994 Amigo devoured to provide head and EFI system.
Heavily damaged by engine compartment fire while driving on March 24th 2018, condemned by insurance company and taken on March 30th 2018 :cry:.

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Re: 1990 2.6 idle problem

Postby TroopDawg » Mon May 03, 2021 4:55 pm

Great info! I dont believe i have the fast idle valve on the passenger fender... i dont have AC. If thats the silver culindar looking valve that atarches to the thermal valve on the water housing... mine is removed.

Near that area though... are a few wires and i have no idea what they go to... heres a photo
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Re: 1990 2.6 idle problem

Postby MotoMike » Mon May 03, 2021 8:32 pm

Those wires do not look "factory" at all? :scratch:
1988 Trooper XS 2.6L Auto Trans 200k
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Re: 1990 2.6 idle problem

Postby TroopDawg » Mon May 03, 2021 8:40 pm

I capped them. Im not sure if they are factory or not. They lead from the passenger fender and through the firewall
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