8-1991 Isuzu Trooper 2.6?

DSUZU said:

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

Click to expand...

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 ??

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

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.

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.