I just replaced the o-rings on my injectors (88 Trooper, 2.6), and now I have that lovely Isuzu surging idle. Once the truck is warm, the surging starts, every time I stop. It will sit there and bounce between 1000 and 2000 rpm, run up to about 2500 and then drop to 1100. If I blip the thottle, it will drop to the usual 900. I have had this problem in the past but it has been intermittent at best, and it seemed to be cured when I replaced the vacuum lines. I am pretty sure that I have the vacuum lines routed correctly, but I just can't be sure. My vacuum diagram is gone from the hood, and I can't be sure I have the hoses routed proplerly. The surging was not an issue prior to the o-ring replacment. I have recently replaced the vacuum lines, so I know there are no vacuum leaks. If anyone has a picture of that vacuum diagram, I would greatly appreciate it.

I can scan the one out of the chiltons manual or take a picture of the one under my hood, if no one has gotten one for you yet, but can't do that until tonight or tommorrow morning.

But two things.... check this link, some good info on trouble shooting the idle speed, explains why it does the bouncing, an idle fuel cut by the ecu to drop it below 1250 if it goes to high and has some good trouble shooting.

http://www.asashop.org/autoinc/feb98/techtips.htm

Also if your coolant is low, it can cause that thermal tree on the top of the thermostat housing to heat up more and think it is over 200 degrees causing it to open. blipping the throttle will rush water over it and cause it to cool down and close.

Rody

Were the Vaccuum lines a pain to replace? I've got what I think is a similar problem. CEL & code says RPM control is high. Heard a whistle one day which I figured is a vac line but haven't tracked it down. Idles high in N takes a dive when I shift to D.

I was going to offer the same thing..
scan the pages from my Haynes & Chilton and email it. I'll bring my books to work tomorrow just in case no one gets to you sooner.
--jeremy

Yes, the lines are a pain. The two on the bottom of the throttle body are the worst. Also, be very careful taking them off of the thermal switch. Old hard crusty lines can be a pain to remove, and the plastic on the thermal switch also gets brittle with age. Why do I know, I broke my thermal switch. Fortunately a little JB Weld and I was good to go (don't worry, I put the thermal switch in hot water to make sure it still worked. Some of the lines are a real pain to get to. Since I had no digram, I did them one at a time. It made a big difference on how the trooper ran. Many of my old lines were hard and cracked on the ends, and I had some big leaks. I used to get the throttle surge all the time before I replaced the lines. I will have to double check all the lines. Thanks for the help on the digram. I should print it and laminate it and then tape to the bottom of the hood. I was kind of ticked the body shop didn't replace it when they put the new hood on.

So let me get this straight, the air regulator is the piece on the bottom of the manifold? It has I believe two large hoses on it and sensor that is connected by a plug that looks like a fuel injector plug? Impossible to get to without removing the tire and going in through the fender well? So if pinch either the line on the throttle body, or the large line on the common plenum (with a warm engine) the idle should not change?? It might be important to note, that my high idle at cold has not worked for at least 100k miles, this is controlled by this valve, yes? I will also check the thermal valve on the thermostat housing. The coolant is up, but I have recently developed a leak, might have something to do with a radiator with 309K miles on it. Thanks for the help.

Also, is it possible your TPS (Throttle Position Sensor) is off just a little? I had idle problems like crazy and so I replaced most of the vaccum lines, cleaned out the plenum, put new gasket on, cleaned out Throttle Body, put new gasket on.

Then I adjusted my TPS and now the idle is closer to normal than it ever has in its 1.5 Years in my hands.

Enlighten me: how does one adjust the TPS? Can it simply be loosened and repositioned? I have nursed my Trooper along for nearly 100k miles. I bought for $175 with just over 200k and a blown head gasket. It has been a trusy steed, but some of these quirks really drive me nuts! I like the EFI, it is a lot more efficient that a carb, but sometimes it can be pain to keep tuned. I suppose it is just a learning curve. And to think I was just getting good with carberators and now I am back to square one with the EFI.

jeepfriend,

check your email, i scanned in the two versions from the chiltons manual, and sent it to the email in your profile. it opens fine in paint, is pretty clear. pretty big though, 1.1mb jpeg.

rody

Thanks man, that will be a big help, now and in the future. I need to buy that chiltons manual. I borrowed a copy one time, and it was pretty helpful. I think I have the surging cured. I found that I had put the clamp, on the large hose on the bottom of the common chamber, a little crooked. So a portion of the hose was not clamped securely. I straightened the clamp and added a zip tie for a little extra security. On the way to work this morning, no surging (and I pushed in the clutch many times just to check for the surging). It is amazing how vacuum sensitive the 2.6 is. It could not have been leaking that much from a crooked clamp, but it does seem to be fixed. So the valve on the bottom of the intake is responsible for the higher idle at warm up? I would like to get this fixed, it would be nice to not have to wedge my CD case between the pedal and the floor, to keep the Trooper running when I scrape the windows in the morning.

You're killing me... a cd case... that's good stuff. yeah, that one under the manifold is responsible for warmup high idle, probably got stuck. Love how it's so conveinient to get to. Glad to hear you might have cured it.

Rody