Surging Idle seems to be a generic symptom of 4ZE1 motors provoked by any number of underlying problems. It is difficulty to distinguish between the problems when they throw such similar symptoms, so beware applying solutions directly that worked for others without troubleshooting your particular motor.

I have seen very similar cyclic revving/surging present from as varied causes as worn/out-of-adjustment throttle body, dirty MAF, tired air solenoids, out-of-adjustment throttle stop, and more. Worse yet, this condition seems often to be transient, presenting only in certain ambient temperatures, under certain engine temperatures. <img src="/forums/images/graemlins/rolleyes.gif" alt="" /> Frustrating! <img src="/forums/images/graemlins/baby.gif" alt="" />

I think many folks end up frustrated by this every-occasional general symptom, and wind up just coping with it until it fades away... That's not to say it isn't worth trouble-shooting, but it can be a bugger to find the actual cause.

Randii

Ahem, we're talking about the 2.8 here. <img src="/forums/images/graemlins/nana.gif" alt="" /> But I agree with you that one's problem and cure isn't necessarily the next person's problem and cure.

Richard <img src="/forums/images/graemlins/patriot.gif" alt="" />

D'oh! <img src="/forums/images/graemlins/scared.gif" alt="" />

Anybody know how to bench test the "EGR Control Solenoid" on a 2.8?

Chilton calls it an "Electronic Vacuum Regulator Valve" and lists the following for testing:
1] unplug connector,
2] disconnect throttle body to solenoid vacuum line,
3] apply 15 in. of vacuum. vacuum should hold - if not replace,
4] apply battery voltage to solenoid terminals. vacuum should drop - if not replace.

Mine fails step #3 in the above. But a new one ($45, in an extended search) behaves exactly the same, straight from the box. ???

Ended up taking back the EGR solenoid. If a new one was exhibiting the same "fault" that my Chilton/Haynes books were describing, I started suspecting that the book(s) was wrong since the book had already steered me in the wrong direction on testing the coil. And the Chilton manual would also help me in making a really stupid mistake (more later).

When I tested the coil per the book it was out of spec. AutoZone said it tested OK, but test obviously couldn't test under load. I decided to go ahead and replace my coil. This got the engine running OK when it was cold. As soon as it warmed up, all engine power was gone and it wouldn't hold an idle at all.

So started checking all the sensors I could find. As JohninLV mentioned, my Thermac valve was leaking. Just a little bit. Replaced that and went ahead and replaced about half of the vacuum connections (they looked brittle).

Engine once again started right away when cold. As it warmed up, engine started losing power. Was missing and backfiring quite a bit. Sounded like timing was way off. It was set at 8-9* and ECU was bumping it up to 18* or so. It sure sounded like timing though. Started thinking about firing order, and looked again at diagrams in Chilton (Haynes doesn't list). The Chilton maual shows the 2.8 to be a four clynder... Since I'd already found a couple of errors in the books I did a search here and sure enough - the firing order of the distributor is in the opposite direction of what books shows. Shuffled around the plug wires and the engine was purring!

Now I was making progress. Reset the IAC, readjusted the idle stop screw (warm idle at a very constant 805rpm), and rotated the TPS so I got an exact .5volts at no throttle. Engine is running far better than it ever has. Top-end is lacking, but I'd expect it with this engine and it's restrictive airflow.

I really need to get a Helm book for this thing. I don't trust the Haynes and Chilton ones anymore. I'm way too rusty at engine work (been almost thirty years since I removed a carburetor) to be chasing ghosts and troubleshooting my frickin' manuals. I'd hoped to find a definitive cause of our problem by methodically replacing/adjusting a single item at a time. But since most all the troubleshooting was done with the firing order all screwed up, makes it hard to know what actually fixed it. Major "D'oh" here... <img src="/forums/images/graemlins/cheers.gif" alt="" />

Gary - thanks for the follow up. My 90 2.8 has a cyclic idle when cold for about 15 seconds 500 - 1000 rpm. Then holds some what steady ~700 - 800 rpm, but slightly rough. When warm, idle is at ~1000 and has a slight "bump" or miss.

I have the same manual you have and I am glad you gave a heads up. I have not had a chance to trouble shoot this issue due to other issues. Helm manual will be ordered today. - JL

Found this post and Im gonna give it a try. I replaced my IAC a while ago (? years) and never reset the minimum air. It seemed to run fine though. Recently at cold start up it..how shall I put it? gasps for air and barley wants to idle. Very much like before I replaced it years ago. I would like to take the IAC out and see what it looks like (possibly gummed up? I don't know.

I have several questions before I tear into this thing.

1. Is it certain that I have a Idle adjustment screw on this rig? (which just needs to be uncovered)
2. In step 3 it says ground the diagnostics terminal (ALDL connector) but I do not know how to do this. Can someone explain further?
3. In step 7 it says remove the plug but the other post that I have read on here and the one at the s-series.org site say the TB must be removed to do this. Can someone clarify this for me please.

Also, the pics of the TB on the .org site seem to be different than mine or maybe I just cant tell. I did a search for it on this site but could not find any pics. I seem to have mixed luck doing searches on here sometimes it works other times it does not. I KNOW this subject has been gone over a million times but I just cant seem to find more info on it here. I saved a post from 2004 on cleaning the TBI and reseting the TPS http://www.4x4wire.com/forums/remli...mp;amp;Thread=532904&Main=532849
But after reading it again I am even more confused because it goes on to say that the instructions given are for a 3.2 or 3.4 ..... so basically I have no idea where to start. <img src="/forums/images/graemlins/confused.gif" alt="" />
I mean I know that I need to adjust the minimum air for certain because I'm gonna have to remove the IAC to check/clean it and as as I said I did not do it when I replaced it before...Alhough I am in CA this rig is Federal if that matters anywhere in this issue. I was reading in another post..related to this whole process that mentioned some difference in the CA and Federal rigs..I don't know..Im tired and cant think straight..heck when I'm wide awake I cant think straight.. Anyway as always any help is greatly appreciated.
Thanks,
J.P.