huh, surely taking the EGR off a running engine would have some very noticable effect if things were not clogged. on the pre-93 intakes the EGR travels through a small passageway cast into the wall of the plenum and exits just behind & below the TB:

you can see how carboned up mine was after 100k. note the hump of the passageway going to the EGR mount.

there is also a 19mm plug bolt right next to the EGR - pulling that makes it easier to inspect/clean that end of the path, while obviously pulling the TB is the only way to check out the exit end.

although I don't think that would explain a low idle. when you manually depress the EGR, it stumbles/stalls because you are opening the loop & pulling in exhaust at low rpm, correct? so a really low idle, if EGR related, would point to the valve(and path) always being open.

Very handy. Thanks for the photo. I was trying to envision where the
port for the exhaust air would end up. This picture takes all of the mystery out of it.

The passage must be corked up good and tight. While I had the EGR off I figured I'd take off the 19mm bolt (while running of course) to see if the chamber was clogged, but it was clean... and still no change in the engine speed. The angle does not look tool friendly. I remember when the transducer port clogged I had to use a drill bit to break up the carbon. Hope that's not the case with this.

I don't think the EGR relates to the low RPM problem. I discovered the EGR as a by product while trying to think through the low RPM. I'm still leaning to a defective temp sensor so I'll take the readings and go from there. I've bypassed the aux air valve which didn't change anything, replaced all the gaskets and triple checked the vac hoses. The air bypass to adjust engine speed in the throttle body is clear. The screw to adjust the idle does change the idle speed, but I run out of threads before I can get to 700rpm. I did not change the position of the throttle stop. I figure the throttle is designed to be completely closed at idle. Adjusting the stop would open it, throw off the air and require adjusting the TPS. I can achieve the same thing adjusting the cable but that's not how it's supposed to work.

I tried advancing the timing a couple of degrees. Performance improved but the ping was too much so I backed it down. It could be that the throttle body is just worn out. I'm not known for working the gas pedal (I pick a speed and stick with it), but when you get near 450K in mileage I suppose everything gets loose enough that even small leaks could add up to enough to cause a problem. I'll keep all posted.

You definitely will get an increase in idle speed if you adjust the mechanical stop. I 'tweaked' on mine a bit and noticed no adverse effects.

Re: the EGR, mine was plugged and I checked all the various passages until finally got to the port where it goes into the intake plenum, just past the throttle body. It's on the floor of the intake passage. I was able to pull back the throttle body enough to get a wire into the passage and clean it out. It was full of gummy deposits. If you can find no other obstructions you may want to check there. If it's blocked badly you'll barely be able to see it.

BTW, lack of EGR can cause pinging in itself. You'll want to get it fixed regardless, as EGR lowers combustion chamber temps and Isuzu exhaust valves sure don't need any more heat!
HTH...........ed

Yes, I would get an increase in speed if I adjusted the screw stop, but the increase would be a function of the butterfly plates opening. That would change the relationship of the TPS and the minimum air settting. I'm keeping it as my last resort option, but really determined to find the solution.

I'm hoping my EGR inlet problem turns out to be as easy as yours. I have notice an increase in engine temps with hi-way driving so the point on combustion chamber temps is on the mark.

I posted over in the thread Pucci opened about relocating the aux air valve some info on an MUCH MUCH easier location to measure the ECM temp sensor... check it out...

I measured mine this evening after driving home from work. Engine DEFINITELY up to temp in this heat/humidity! I was reading 248 ohms. Last night when the engine was cooler (but not "stone" cold, still probably 90 to 100 degrees) I was reading 1.25 Kohms, so it seems the sensor is not my problem. I also did the test with the AAV that Pucci outlined, and I don't believe that's the problem either.

I'm leaning toward a crudded up throttle body, or dirty injectors... I'm planning on pulling the TB this weekend when I adjust the valves and re-torque the bolts on my new head and cleaning it out real good...

C/YA!
Jeff
(exit 109)

Talk about unintended consequences... Using Pucci's photo and Ed Mc's suggestion on the throttle body, I unbolted the TB, pulled it back, took out the 19mm bolt and after 15 minutes of prodding with a piece of #12 wire and blasts of cleaner (Valvoline synthetic carb &throttle body: dissolves carbon like no other) a lump of junk floats out the 19mm drain.
OK! Bolt it all back and fire it up. Barely enough RPM to keep it running, but the push test on the EGR valve confirms I've got my EGR circuit back.

So now I take it for a test ride. Seems good, hesitation is diminished, but as I drive the temp guage climbs; past the quarter mark where I'm used to seeing it, past the halfway point, past the 3/4 mark and settles
just about 7/8 up the scale. Figuring "this can't be good" I drive home, pull in the drive and lo and behold not only is the RPM up, it's way up,
about 1500. I adjust the screw to bring it down, check the timing and it's off (almost TDC) so I reset it for 12 degrees BTDC. Then check the thermal air valve on top of the stat housing and sure enough it's open. That explains the RPM. I go for another test ride. Temp climbs again, but this time settles at 3/4. I've had enough for the night.

Starting it up today I have to keep my foot on the gas to keep it from dying (does this sound like the aux air or what?), but after a few minutes it settles to it's usual 400 RPM and the temp gauge stays at the 1/4 mark. Driving to work the temp starts the climb and settles at 3/4 on the gauge. I stop and confirm the thermal air valve is open and RPM's are up to the 900 RPM I adjusted it to the night before. I pull in to work and grab the handy infra-red temp scanner (it's nice to have toys available) thinking that 1/2 on the temp gauge (cools off quick once I'm off the hi-way) has got to be too hot. It reads 185 degrees on the thermostat housing. I read the exhaust at the EGR tube: 660 degrees. I read the common chamber 135 degrees. Nothings too hot.

So... Somebody correct me if I'm wrong; the normal warmed-up operating mode for the 2.6 I-TEC is >180 coolant temperature with the thermal air valve open. I'm thinking the introduction of 600 degree exhaust gas (via the EGR valve) to the common chamber probably tweaked the sensor reading up, but not outside of normal. And what would be too hot?

Anyway, I seem to down to a cold start idle problem so I'm back to the
aux air versus the temperature sending unit. Maybe I should just crack open the wallet and replace both seeing as they've been in place for 16 years
<img src="/forums/images/graemlins/smile.gif" alt="" />

If the valve on top of the Tstat opened, it indicates OVER heating... I believe that should normally be closed.

The test for the ECM temp sensor is EASY... but you would need an el cheapo Radio Shack ohmmeter to do so.

If on a cold start, your aux air valve is OPEN, i.e. strong vacuum at the hose end near the TB, and that vacuum goes away in like 5 minutes, then that valve is most likely OK.

If you are running hot enough for the valve on the T-stat to open, you've got other problems you need to find and resolve.

How's the condition of your radiator ?

C/YA!
Jeff

Having read this whole thread a couple of times, I would run a compression test. The totality of the symptoms is beginning to sound like a bad head/head gasket.

I'm keeping it as my last resort option, but really determined to find the solution.

You seem to be totally averse to adjusting the stop, but you are also taking a shotgun approach to this problem. You got to have a plan, man. Finding the EGR problem was only by accident. It was good to find it, but it was ancillary to the inital problem.

Get a manual. I don't have mine with me right now, but the throttle stop is set to some specific gap, using a feeler gauage. Then, set the TPS. Again, another quick and easy thing to do, again, it requires some feeler gauages.

Then, set the idle speed using the air bleed screw. Again, making sure the passage is clear. After that, pull the vaccuum canister purge line, plug it and then set the timing. Rechecking the idle speed and then the timing to make sure they are correct.

Once you are there, then you can start chasing the other gremlins. I think you have a combination of timing and idle speed issues to work out. The temp spike can easily be a function of timing on the 2.6. I would even suggest looking for other vaccuum leaks or bad vaccuum lines.

Finally, start dealing with the aux air valve. Check the lines. Heck, plug them and see how it runs. If it runs better (after being warm) then maybe the valve is bad. I do have to say, I have never heard of one going bad. I have had lines pop off or maybe they crack (massive vaccuum leak, instantly) but AFAIK, the valves are relatively bomb proof.

Good Luck,
Michael

"You got to have a plan, man."

Yeah, but the plan isn't working. This all started back in the Spring readying the beast for inspection. It's had a low idle for a while but I figured a tune-up was in order and having read the number of posts with intake gasket problems I figured I'd change the intake side gaskets while I was at it (200,000 miles had passed since it was last done). Did it all by the book (Haynes) adjusted valves, changed out plugs, cleaned everything ('cept for that EGR passage I didn't know existed) set the TPS while I had the throttle body off (using your very good instructions from a previous post, Michael), put it all back together and... low idle. I blew enough carb cleaner through the air bleed passage to confirm there's nothing blocking it. I just can't get the RPM's
past the 450 mark even with the screw backed all the way out. Without the RPM's at the right level I can't set the timing correctly so I approximate. I think what I'll do is removed each vacuum tube that hooks into the common chamber and plug it to see if the engine speed changes. I replaced all the rubber tubing two years ago, but I've always been suspicious of all those little pneumatic switches mounted on the fender walls.

Oh, and I passed emissions; very low hydrocarbons (72), average CO
and just under the wire on NOx. I'm pretty sure the NOx issue was a function of the plugged EGR. I've got no indications of a head gasket problem (no milkshake in the oil pan, no brown globules floating in the radiator, no steam out the tail pipe), mileage is excellent; If I could just get past this low idle and slight stumble on accleration I'd be happy. I'll agree the aux air seems bullet proof. By-passing it on start up changed nothing. Plugging it when warmed up also changed nothing so the pointer goes back to the temp sensor.

And the drive in this morning the temp guage stayed at the 1/4 mark...might have had something to do with the fact it was 70 degrees outside instead of 90 degrees... Thank you for confirming that thermal air valve "open" means "Too Hot". It didn't seem right adjusting the engine speed with all this air bypassing the throttle plates.