my 2.8 idles at 1500 rpm and surges between 1500 & 1000 , also getting 15 mpg. What do you guys think? , vacuum leak or egr valve problem .

it got a 2.8?

It would not be egr, because egr does not work at idle. also if it was a vacuum leak it would be a steady high idle. so my sujestion would be chek out the IAC control. could be dirty or just plain bad.
Don

second the Iac valve check.

High idle on the Fiero 2.8 is classic for a broken or cracked EGR tube. It normally fails right at the top where it attaches to the underside of the intake.

JazzMan

You can do the classic "idle air bleed hole smother" by putting your finger over the
idle air hole just behind the rubber intake. I know the intake is a bit of a pain to remove,
but when you get it off, you can see the small idle air hole just before the butterfly.
Put your finger over the hole and if the motor dies, you don't have a vac leak (from my
experience anyway). I guess you could just put the palm of your hand over the end
of the whole throttle body too, just haven't thought of that till now.
NOTE: If you have "office boy hands" you might get a slight hickey.

quote Originally posted by TennT: NOTE: If you have "office boy hands" you might get a slight hickey.

lol, I am going to try that to nite. Mine idles around 1500 and 1000 to. I replaced the egr so I know its not that. I just need it to go throw inspection. I am rebuilding a 3800 right now so I will switch them soon. Thanks for the helpful tips

Mine does the same thing...always has and only has 9k on a rebuild. Replaced all the sensors and everything else w/ not change. I figure it is the bigger cam that I put in. Engine runs awesome cept for the high idle. No harm there.

Frank

Mine also has idle problems that seem to be unstopable. I just tell people its a hot rod.

Heres what I always do, works like a charm. Take a suitable object, I like to use a tidycats cap, anything that will slip snugly over the throttle body will work, tape it down if neccesary. Before putting it on, drill a small hole in it, and thread in a threaded nipple. Put it on the engine, then regulate your air compressor down to say 15psi. Connect it to the nipple with a vavle, and partialy open the valve. Listen for air leaks, and/or spreay the engine with soapy water. Ive found a ton of air leaks this way.

A friend of mine had a 2.8 doing the exact same thing. We replace his distributor and it fixed it.

quote Originally posted by 86GT3.4DOHC: Heres what I always do, works like a charm. Take a suitable object, I like to use a tidycats cap, anything that will slip snugly over the throttle body will work, tape it down if neccesary. Before putting it on, drill a small hole in it, and thread in a threaded nipple. Put it on the engine, then regulate your air compressor down to say 15psi. Connect it to the nipple with a vavle, and partialy open the valve. Listen for air leaks, and/or spreay the engine with soapy water. Ive found a ton of air leaks this way.

WOW...I never thought of doing that. Very good idea.

Frank

If everything is working properly, no exhaust leaks, no EGR leaks, and
the engine is properly tuned, you can go through the IAC system.

Idle is controled by the IAC valve (idle air control) via the computer and
is not adjustable.

You can go over the system if your not happy with where it is idleing.
Proper idle for the V6 is roughly 900 RPM.

The set screw in the throttle body is for minimum air flow through the
throttle plate which is often misunderstood as the idle screw. Any tweaking
of the throttle stop screw will give the ECM fits. The ECM wants to be in
control of the idle and is not happy when it can't control it. If the normal
learn limits of the ECM are exceeded, they will be reset to nominal, causing
an erratic idle.

The IAC and associated passages need to be clean to work right. Remove the
IAC carefully. You can clean it (the nipple) using carb cleaner and a small
brass brush or rag. At this time also clean the throttle palte. Once clean,
install the IAC back in the throttle body and reconnect the IAC wires.

For the ECM to properly control idle, the throttle stop screw must be set
for "minimum air". This is a process that sets the idle with the IAC fully
extended. To fully extend the IAC, jumper ALDL pins A and B together (just
like when you check codes) and turn the key on, but do not start the car.
With the key on, not running, and in diags mode, the ECM will keep trying to
fully extend the IAC. After 30 seconds or so, pull the IAC connector off the
IAC *before* doing anything else. This will capture the IAC fully extended.

Now pull out the jumper in the ALDL, and start the car. Typically the
"minimum air" idle speed is in the 500 RPM range. I find the car can bearly
run at 550. So as long as you can get it to idle on its own between 600 &
700 your good. Set the idle using the throttle stop screw. (The engine
should be fully warm to do this.) Now shut the engine off and reconnect the
IAC wires. The ECM does not know where the IAC present position is, so pull
the ECM fuse (or disconnect the battery) for 20-30 seconds. (This will cause
a complete ECM reset of all learned parameters, including the learned IAC
ones. Then reinstall the ECM fuse.

Turn the key on, wait 10 seconds or so, and turn the key back off. This will
now reset the IAC to a known key-off "park" position. Now start the car. The
engine should idle properly under control of the ECM. There are some learned
values, such as an IAC offset for A/C, etc that need to be learned, but this
will happen under normal driving conditions. I suggest driving the car right
away under all conditions. Stop & go, steady cruising over 45 mph, full
throttle, and so on. Pull over a few times and turn the car off, then
restart it. The IAC can only learn X amount of counts with each run
position. If everything else on the engine is in good condition and
operating properly it should be around 900 RPM after coming to a complete
stop with slight variations and improve over time.

Mine is almost rock solid at 925 RPM.

Thanks for everyone's suggestions. I wonder if the screw has been adjusted on the throttle plate where should it be "reset" too, or at. Half way down the hole, all the way up, or all the way down (screwed all the way in)? I hope that makes sense.

If the cap's missing off the screw adjustment throttle stop then it's probably been messed with, likely trying to bring the idle down because a broken EGR tube raised the idle.

To set the idle correctly requires monitoring the IAC stepper counts via the ALDL cable, it's not really something that can be done otherwise.

JazzMan

quote Originally posted by JazzMan: To set the idle correctly requires monitoring the IAC stepper counts via the ALDL cable, it's not really something that can be done otherwise. JazzMan

Really?

I guess you missed my long and detailed post.

I wrote that over a year ago and post it when I feel it might help somebody solve their 2.8 idle promlems.

Remind me next time to not bother because it's something that can't be done.

skybax, I think and I hope you may have solved my problems. In fact, after reading your post about setting the throttle stop screw a light bulb just went off in my head, and I think I'm beginning to understand this thing. My car is an '87 GT and it's been sitting since 1995. My father drove it in 1995 and I don't remember any real troubles except for an unstable and fast idle. After getting the car out of storage, it needed a fuel pump, screen, filter, and the injectors cleaned. I was pleased that it started right up, however, it wasn't running good. Since I wasn't the one driving the car before, I don' t have much to compare it too, which is when I found this forum. I have been researching here quite a bit over the last few months, but just decided to register. I have learned a lot so far, there is some good knowledge on this site ! The car had an EGR code and TPS code, I replaced both of those, including the EGR solenoid, but it still idled bad. I have read that it's "the nature of the beast" but I can't help but think there must be a fix. For grins I replaced the IAC, MAP, coolant temp sensor, ignition coil, it even got a new distributor after it "mysteriously" would quit for no reason on the highway, but immediately restart (before you even stopped sometimes) and after the restart run fine like nothing ever happened. Well I got it reliable enough to take it to it's new home, I drove it from Orlando to CIncinnati last week, and now that it's "home" i'm doing some more work on it. The throttle is sticking at idle. I removed the throttle body to investigate the sticking and the IAC bore, still trying to cure the surging idle. The throttle cable is free, and I noticed the throttle plate closes completely, almost wedging itself in the bore, I also noticed the idle stop screw was backed out several turns, literally 1/8" away from touching anything. I know the idle is controlled by the ECM, but I figured the screw wouldn't even be there if it wasn't supposed to do something, which is when I found your post. I'm confident if I open the throttle slightly with the screw, it won' t bind anymore, and I'm praying that will also fix my surging, maybe with the throttle completely closed and NO air geting throught it, the IAC can't compensate that much. In any case, I'm glad I learned something else today, but I can't test it since the fuel tank is out.

My fuel gauge wasn't working, I was happy to hear you can still get a sending unit from GM , but over $400 !!! so I removed mine, and cleaned the wiper and it's working again, however my tank is so rusty, I'm afraid to put it back like that, anyone know where to buy a fuel tank? Have you heard of cleaning them with toilet bowl cleaner? My neighbor suggested that, he said it will eat the rust like crazy.

[This message has been edited by BBriBro (edited 06-04-2005).]

just for my two cents, my 2.8 used to have high idle, i was using 87 octane...switched to 89 and it lowered to about 1000 rpm where i believe it should be around. it WAS idling at 1500...so if youre using 87, theres an idea.

The most common cause of high idling is a vacuum leak. Here's a safe way to find a vacuum leak. Get a spray bottle and fill it with water. With the engine cold, start it and start spraying all of the vacuum hoses, the EGR tube and around the plenum. If the engine slows or stall when you shoot water in one spot then check those lines for breakage or splits. A fine water spray mist usually won't hurt the MAP sensor, electrical connectors, dist module or EGR solenoid but it's a good idea to try and avoid spraying these anyway. Another way to find vacuum leaks is the smoke test, but you'll need a smoke generator to fill the plenum and a light to watch for escaping smoke. This test is always done with the engine off. .

I agree with the "most common" causes of a high idle, but sometimes they are not so easy to troubleshoot. The factory service manual suggests a "quick test" by entering diagnostic mode, (forcing the IAC closed) then disconnecting the IAC, and starting the car, it should not idle above 800 RPM. If it does, then there is a leak that the IAC cannot compensate for. In my case, I found the throttle stop screw backed completely out, by several turns, my car would not idle at all without the IAC, the throttle was completely closed. I don't have anyway to monitor the "counts" of the IAC but I bet it was completely out of spec.