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Discussion Starter · #1 ·
I have a hose coming up from the IAC valve but is not connected to the throttle body. See second pic where you will see the hose with the bolt at the of it.
The throttle body has an adjuster screw on top.

I have a 1988 trooper 2.6 and i dont think the throttle body that is on there is correct. Which year is mine from?

Can i just swap the correct throttle body or do i need to replace the upper intake manifold as well?
 

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Discussion Starter · #2 ·
Update; i was reading theough some posts and i may have a later model throttle body, maybe a 94? Can someone identify please?

Since i have the IAC at the bottom of the manifold, does that mean i have the correct manofold for my year?

What should i do? It obviously will not idle when cold.
 

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You have (at least) the upper plenum and throttle body from a later model (1993 and up) 2.6. The advantage (?) is the later intakes had larger diameter runners. The disadvantage is the later (round) throttle bodies flowed less CFM than the earlier two barrel throttle bodies (according to Jerry, our local REAL Isuzu expert - the main one). What color re your injectors? The originals were a tan color, from my experience, the later ones were red. They take different injectors. The injectors go in the lower intake and can't swap from one manifold to the other. Dennis
 

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Discussion Starter · #4 ·
You have (at least) the upper plenum and throttle body from a later model (1993 and up) 2.6. The advantage (?) is the later intakes had larger diameter runners. The disadvantage is the later (round) throttle bodies flowed less CFM than the earlier two barrel throttle bodies (according to Jerry, our local REAL Isuzu expert - the main one). What color re your injectors? The originals were a tan color, from my experience, the later ones were red. They take different injectors. The injectors go in the lower intake and can't swap from one manifold to the other. Dennis
I just checked. The injectors are tan in color.

What do i do with the IAC hose? Where does that connect to now? Did the 93 and up have iac hose routing?
 

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I don't remember exactly what the late 2.6 used. Where does the OTHER hose go to? IIRC one hose goes from the intake to the IAC (under manifold). The other hose goes from the IAC to the air intake tube between the air filter and the throttle body. Dennis
 

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Discussion Starter · #6 ·
I don't remember exactly what the late 2.6 used. Where does the OTHER hose go to? IIRC one hose goes from the intake to the IAC (under manifold). The other hose goes from the IAC to the air intake tube between the air filter and the throttle body. Dennis
So yes, i have one hose coming from iac to the bottom of the manifold and the other hose comes up through manifold and is plugged with a bolt. That end would have gone to the pipe on the throttle body which seems to be from 93 and up model as you stated.

How do i confim what year the TB is from?

How do i resolve this?

Sorry lots of questions and problem solving here.
 

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Okay. I just checked. Page 49 of my build thread shows what you need. There is a nipple at the bottom center of your intake plenum (upper chamber where the throttle body goes). A hose is SUPPOSED to go from this nipple, to the IAC, to the air intake tube. The older throttle bodies had a nipple on the throttle body. Dennis

EDIT / update The plugged hose should somehow attach to the air intake tube. Your throttle body is a 1993 - 1997
 

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Discussion Starter · #8 · (Edited)
Okay. I just checked. Page 49 of my build thread shows what you need. There is a nipple at the bottom center of your intake plenum (upper chamber where the throttle body goes). A hose is SUPPOSED to go from this nipple, to the IAC, to the air intake tube. The older throttle bodies had a nipple on the throttle body. Dennis

EDIT / update The plugged hose should somehow attach to the air intake tube. Your throttle body is a 1993 - 1997
When you say the tube is supposed to go from IAC to air intake tube, do you mean for the 93 to 97 TB?

I confirmed a tube going from iac which is at the bottom of lower phlenum to the nipple at the bottom of upper phlenum

See pics

First pic shows the tube from iac valve.

Second pic: should the sensor (blue) be there and should there be vaccum lines coming from there? To where?

Third pic shows the intake tube..should i add a T and route that hose from iac that is blocked with the bolt to the T ??
 

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Last picture: it appears to be an earlier tube (but they may be the same). Hose on the rear goes to crankcase VENT nipple on valve cover. Hose on FRONT is (should be) the one that leads to the IAC. On the older 2 barrel, the hose hooks to the throttle body on a nipple that is mounted on the INCOMING air side of the throttle plates.
The blue "thing" that is broken off is the thermo vacuum valve. This allows no vacuum when cold. When warmed up, it allows vacuum to the EGR transducer (IIRC, your EGR is removed). Note that when my EGR tube broke and I had to disable my EGR syatem, I got WORSE gas mileage than before the tube broke. After replacing the tube, my gas mileage went back to normal. On older, non compensating CARBED engines, the EGR system was a power robber and gave worse gas mileage. On EFI systems the system is designed to have EGR, so it compensates for it.
From the pictures, it appears your vacuum hoses are aging and cracked. This usually causes a higher or erratic idle. If someone adjusted the large mixture screw on your throttle body to compensate for this, that could also be part of your problem. In adjusting that screw, I advise only making a 1/4-1/2 turn at a time. Drive it, see how it works, readjust as necessary. In = lower idle out = higher idle. Dennis
 

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You have the same throttle body as I do on my 1993 Rodeo, I'll get you a picture, you have the wrong air intake tube for the throttle body.
 

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See how the section just before the TB has a hose fitting? Right where the ignition coil wire to the distributor is on yours. I'd advise taking Dennis' advice and changing all those hoses too. It's really difficult to find bulk generic hoses that will do the job, one thing you can harvest off a later V6 (every Isuzu at every junkyard is a V6 in my experience) is sections of hoses that are the exact right size and cut them down to approximately the same shape/curve.
 

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If I had that problem I'd probably Dremel out a hole through the piece you do have, use the closest to the right diameter brass fitting from home depot's plumbing department and JB weld it into the hole. You'd have to be extremely lucky to find that plastic tube and that's pretty much how Isuzu did it anyway mine really wants to slide in and out.

Imagine that the hole in my wrench handle is a hole you just put in that intake tube and you'll get the idea.

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Discussion Starter · #13 ·
Thanks guys. I really appreciate. Glad to have such a supportive and resourceful community of enthusiasts. I will provide an update once i get that completed. I am planning on pulling the manifold and replacing gaskets and yes vaccum lines, duel lines etc. Not sure but this thing must have been sitting for a while.
 

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Shadesh. I just figured this out today and I've thought about it every day for about a month. What we both have is a late 1993 and up federal/non-California throttle body swapped onto California trucks. The California version of the single/round throttle body would have a completely different EGR valve, about 5 other EGR parts, and a different back pressure transducer that's red plastic on top black plastic on bottom. Mine has the right intake tube because my truck came with it for the late 1993+ CA version of the round/single throttle body, your truck doesn't have the right plastic air intake tube because your truck came with the old 2bbl/oval throttle body. Luckily your truck has the right back pressure transducer for a vacuum operated EGR and you probably don't have a bunch of extra EGR components mounted to your valve cover to confuse you, that your computer wants to talk to like on mine. If you search "straw trick egr" on here you should find everything you need to run the EGR with what's on your truck provided it works, just know you can't trust the vacuum diagram under your hood and you'll probably have to experiment to find the best way to route your vacuum lines. You'll want your EGR set up pretty close to how it's discussed in the posts where the "straw trick" is discussed, your IAC hoses routed like they are on my hood diagram, and the rest as close as you can get it to your own hood diagram, that's a good starting place at least. Attaching my hood diagram and some measurements on the hose to your IAC, it's not going to run right with that bypassed.

Mine was running pretty great with the EGR valve and it's 5 other components that are still on the truck bypassed completely and my Rodeo's computer has more than one connection to the EGR system, shouldn't be too big of a problem for you. There's a lot of posts on here about cleaning your EGR valve and testing that the EGR Back-Pressure transducer functions (very likely that it's no good). I blew a head gasket when one of the coolant hoses off the bottom of that throttle body cracked, there's 2 of those and 2 vacuum ports on it, the vacuum ones are smaller.

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Discussion Starter · #15 ·
Hi Timmay, Thank you for your insight here. Appreciate you taking the time. I read through and still digesting.

In your diagram, where is the IAC valve? I dont see it. I was yold i could plumb the hose coming up from IAC, that would have connected to a nipple on the original oval TB, to the air intake hose close to the TB.

It sounds like i ha e the correct back pressure transducer and EGR for CA?

I will read up on the "straw trick" write up as well and repoert back.

Here are some pics of Egr, transducer etc.
 

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IAC valve is located UNDER the intake manifold. Very difficult to get to. Dennis
 

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I had my valve cover off until last night and I have yet to reassemble everything else. I should be able to get you a picture this afternoon of how it's in there. In 1993+ CA version of the throttle body they had an electrically operated EGR valve opposed to the vacuum operated EGR you see on your truck, which is where the extra VSV, vacuum tank, orifice, solenoid, etc. come in on my diagram at the top. Your truck probably had none of that. You will probably need a "thermal valve" as well as the back pressure transducer to have your EGR configuration "correct", it's not the three port thermal vacuum valve (which you also need and it's impossible to get get them) which would be plugged in to the top of the thermostat, this one is a two port F connector and I believe the plastic on it is blue, and it would also be under your intake manifold in the vicinity of the IAC.
 

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The IAC's location is where I thought the ECM/Idiot light connected engine coolant temperature sender was after the first half hour I looked for it (very similar connector), but on mine at least, it's even deeper under the intake and more impossible to get to without pulling the head and intake.
 

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Discussion Starter · #19 ·
View attachment 123764

See how the section just before the TB has a hose fitting? Right where the ignition coil wire to the distributor is on yours. I'd advise taking Dennis' advice and changing all those hoses too. It's really difficult to find bulk generic hoses that will do the job, one thing you can harvest off a later V6 (every Isuzu at every junkyard is a V6 in my experience) is sections of hoses that are the exact right size and cut them down to approximately the same shape/curve.
I think I understand now.. so that fitting on the hose fitting closest to the TB is what takes the hose from the IAC, correct? I will try to find a round hose fitting too so it fits better on the later TB which has the round port. Thank you sir.
 

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Discussion Starter · #20 ·
Can someone explain what should be coming out of here and where should it be going to? Or do I not need it now because I have a later model round port TB? I circled the part in red.

Can I use the Acedelco part as a replacement (if I still need it for my 1988 Trooper 2.6) or I need to find the specific one for my year/make/model?
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