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Old 08-19-2006, 08:39 AM   #57
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Originally Posted by garry
Bummer I have the same problem and was looking forward to you having a fix. My problem came with the RV. Logged over 5,000 miles with the fast idle.
The part I hate most is putting it in gear, I know that has to be hard on the transmission plus stopping with a fast idle is hard on the brakes.
I still suspect a vacum leak. I did have a broken vacum line that caused the AC to blow on defrost all the time but that wasn't enough of a leak for the fast idle. The other reson I suspect a vacume leak is it takes very little to have the AC to go into the low vacume mode. It will change from dash air to defrost or AC compressor cuts off under a medium load.
TB gasket checks OK but I haven't changed it out I don't like throwing parts until I have a better handle on the cause and not the symptom.
Ain't this fun ????????????
Best of luck and please keep us posted.
Garry
Garry, my empathy is extended to you. Have you checked all the different vacuum driven items, one at a time, that connect to the TB or intake manifold? That's pretty simple and easy do do, in most cases. And it's a way to eleminate things with certainty. A golf tee makes a good plug for most or the vacuum ports. If you find the trouble maker, the engine will idle normally when you do. Bill
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Old 08-19-2006, 10:22 AM   #58
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Tbi idle control....

actually, there is one (at least on the 350 TBI's..). I remember when I did my Astro engine swap (v6 to 350 v8), that there is a screw in the front driver's side of the TBI. However, you must drill out a silver plug to get to it (as you look at the TBI from the front bumper, look on the driver's side of the TBI facing you.

Good luck!
Marc
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Old 08-19-2006, 01:09 PM   #59
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EGR Valve

Terry, I set out to check the EGR valve and ran head-on into "nothing is ever easy", again! I am finding that my 94 GMC 454 engine has several engine components located where they are positioned on 95 and newer engines (like that Electronic Ignition Plug). What's that all about......they have done that just to confuse me! I looked for your typical EGR valve, with the vacuum connection, ect., and found NONE! Got out the Haynes book again and discovered several versions of EGR valves were used, depending on the year. My 94 has the EGR valve version like what is supposed to be on the 96 thru 2000 models, according to Haynes. And, it is located nowhere near where they say it is! It is the type called Linear EGR Valve. Located just to the left of the TB and connected to the intake manifold by two bolts and a gasket and with a 5-pin electrical connector. No vacuum connections what so ever, nor exhaust connections. I guess that is all concealed inside the engine block. Haynes says any trouble with it is usually manifested by rough idle. Since that is not my problen, I assume the valve is good.....but, there could be a vacuum leak in the gasket at the mounting base! I will check that with the WD40 when the engine cools down a bit. I will also check to see if there is a hidden idle adjustment, as Marc suggests, in post #9. More later......... Bill
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Old 08-19-2006, 04:51 PM   #60
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Quote:
Originally Posted by lebolewis
Terry, that Carb cleaner is corrosive stuff!! Are you certain that it will do no damage to the engine? Even with a manifold gasket leak, how does the Carb cleaner get into the combustion chambers and cause the engine to speed up? Bill
If it's bad, a little spritz is all it'll take. You shouldn't need to hose down the inside of the engine, I have done this with no problems.
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Old 08-19-2006, 09:11 PM   #61
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Bill ,I had mentioned to you about the throttle plates being shut ,I had said
all the way ,but really there needs to be a bit of opening obviousely,and my
mentioning it was to help with the checks your doing .My point was that if they are being held open somehow too much .Did you have a chance to block the IAC opening?The EGR linear type is all electrically actuated ,the most
common problem with them is a small piece of carbon stuck in the pintle,
which happens all the time on 4.3 V6 astros ,mostly ,it would as you said
idle rough ,not fast.you have Im sure pinched off the brake booster hose?
unless you have hydro boost (no vacuum booster).Well keep us posted ,
and I will get back to you this week unless you locate the trouble sooner.

Scott
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Old 08-19-2006, 09:24 PM   #62
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Quote:
Originally Posted by scottanlily
Bill ,I had mentioned to you about the throttle plates being shut ,I had said
all the way ,but really there needs to be a bit of opening obviousely,and my
mentioning it was to help with the checks your doing .My point was that if they are being held open somehow too much .Did you have a chance to block the IAC opening?The EGR linear type is all electrically actuated ,the most
common problem with them is a small piece of carbon stuck in the pintle,
which happens all the time on 4.3 V6 astros ,mostly ,it would as you said
idle rough ,not fast.you have Im sure pinched off the brake booster hose?
unless you have hydro boost (no vacuum booster).Well keep us posted ,
and I will get back to you this week unless you locate the trouble sooner.

Scott
Scott, he has Hydroboost, and I was thinking more along the lines of a leaking base gasket for the EGR valve. I am also thinking maybe his throttle linkage or cruise control unit was holding the throttle plates slightly open, like I think you mentioned a while back.
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Old 08-19-2006, 10:20 PM   #63
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Haven't had time to check it all but it's not the TB gasket.
The idle does slow down from 1200+ to around 1000 rpm once the engine starts to warm up. The cruse control also will give WOT if engaged and I think that may be part of the same problem. Just need more time and some way to do the testing in less than 100 deg temps.

Garry

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Old 08-20-2006, 08:16 AM   #64
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Quote:
Originally Posted by scottanlily
Bill ,I had mentioned to you about the throttle plates being shut ,I had said
all the way ,but really there needs to be a bit of opening obviousely,and my
mentioning it was to help with the checks your doing .My point was that if they are being held open somehow too much .Did you have a chance to block the IAC opening?The EGR linear type is all electrically actuated ,the most
common problem with them is a small piece of carbon stuck in the pintle,
which happens all the time on 4.3 V6 astros ,mostly ,it would as you said
idle rough ,not fast.you have Im sure pinched off the brake booster hose?
unless you have hydro boost (no vacuum booster).Well keep us posted ,
and I will get back to you this week unless you locate the trouble sooner.

Scott
Scott, I plan to check the EGR gasket today and I will also plug the IAC hole and see if the engine stops running. Seems like it should stop unless it's getting air from somewhere!! The challenge is to find something that will completely plug that odd shaped hole and not be sucked into the intake manifold! One of the first things I checked was the accelerator cable and the cruise control cable and they are slack when at idle, so that is not the problem. I have already visually inspected the throttle plates and they look like they are closed almost all the way. I also tried putting a little "closing" pressure on them with my hand, when at idle, and the engine sputtered and started to stall. I think they are OK and not part of the problem. More later........ Bill, the budding expert on fast idle problems! ......and just about everything else, too!
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Old 08-20-2006, 09:24 AM   #65
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I have been following this thread since it started. Bill, hang in there! When you get this issue resolved you will know more about you engine then you ever wanted to!
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Old 08-20-2006, 12:18 PM   #66
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Quote:
Originally Posted by lebolewis
Scott, I plan to check the EGR gasket today and I will also plug the IAC hole and see if the engine stops running. Seems like it should stop unless it's getting air from somewhere!! The challenge is to find something that will completely plug that odd shaped hole and not be sucked into the intake manifold! One of the first things I checked was the accelerator cable and the cruise control cable and they are slack when at idle, so that is not the problem. I have already visually inspected the throttle plates and they look like they are closed almost all the way. I also tried putting a little "closing" pressure on them with my hand, when at idle, and the engine sputtered and started to stall. I think they are OK and not part of the problem. More later........ Bill, the budding expert on fast idle problems! ......and just about everything else, too!
It looks like you found the problem, the throttle plates are not closing properly. When you pushed them closed, the engine sputtered and almost stalled until the IAC could open and provide idle air. Fix the throttle plates so that they close and you should have your problem fixed.
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Old 08-20-2006, 12:39 PM   #67
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OK guys, I removed that air cleaner housing and filter again, for the 673time!!

FIRST thing I tried was plugging the "Bean Hole", the IAC port on top of the TB where the IAC gets it's air. Getting that odd shaped hole 100% plugged is not easy to do!! After several unsuccessful attempts, I finally tried a Wal-Mart plastic bag, waded part of it it into a small ball and stuffed it in there! Shazam! That works! The engine slowed considerably, but didn't completely stop. I had to hold on to the plastic ball for fear that part of it would get sucked into the intake manifold, so I couldn't get around to see my Tach to read the RPM, but I would guess about 500 RPMS. Keep in mind that 500 RPMs is only about 100 RPMs slower that what's suppose to be normal. When I removed the plastic wad, the engine speed went way up, because the IAC was commanded wide open by the computer. Then the computer closed the IAC, part way, until the idle speed was again 900 RPMs. What does this confirm? Two things, I think. 1) The IAC definately works and follows the command of the computer. 2) the computer thinks that an idle speed of 900 RPMs is OK and adjusts the IAC to keep it at that speed. Now that would suggest that it is NOT a vacuum leak!! For example, if there was a small vacuum leak somewhere and you plugged it, then the Computer would just open the IAC a little more until the idle speed was again at 900 RPMs! RIGHT? Seems to me that is what the computer is now doing. What that then suggest is that it is some other non-vacuum device sending the computer the wrong info that makes it think that 900 RPMs is OK. Right? And I think that I have checked all of the other sensors and they checked good. I havent actually checked the coolant resistance at operating temperture, did it when it was slightly warm, it supposed to be about 200 ohms. I will do that again at running temp, to be certain. Now what does that leave? ......the Computer itself!! That sucker could be the trouble maker! Hold those thoughts and I will come back later.

The SECOND thing I did was check for a vacuum leak around the EGR base gasket. I sprayed WD40 all around and got no indications. NOTHING! At this point I have to say that the WD40 test is a bit questionable in my mind. Why? Because when I sprayed a lot of WD40 directly into the IAC Bean Hole, and that goes directly into the intake manifold, I get a very brief increase in engine speed, not a decrease as was earlier indicated by the person that suggested the WD40 test. The increase only last for about 1 second, and it's gone. Now think about a small vacuume leak around a gasket. You are only going to get a tiny bit of WD40 in there and the engine increase will not likely be noticable, if at all. That's what I have concluded. The unlit propane torch with a small pointed flame orfice sounds like a much better way to verify leaks. That propane would likely speed up the engine a lot! Any comments by those who have tried this?

Some facts: Idles at 900 RPMs in neutral. 700 RPMs in gear with AC on (that's about 100 RPMs faster than normal). So, whatever the cause for the fast idle, it's a small thing....not a big thing. That's why it's so hard to find! I'm still looking.

Oh, There is indeed an idle adjustment on my TBI as Marc suggested in post #9. Can you believe that?!! I can see a threaded stop on the accelerator side, up against the stop on the accelerator where it is attached to the rod that holds the plates in the TB!! The adjusting end of the threaded adjustment is sealed with lead on the front of the TB. It's probably set during the mfg of the TB and then sealed. Not sure I really want to tamper with that! What do you think? Bill
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Old 08-20-2006, 01:20 PM   #68
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Quote:
Now what does that leave? ......
the base timing of the engine.

john
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Old 08-20-2006, 02:43 PM   #69
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the base timing of the engine.

john
And he already checked that, it was perfect. WD40 will INCREASE the engine speed if sprayed into an intake, as it is mildly flammable. I used it for starting fluid for my old 6.9/7.3's that I have had in the past.
Anyway, if you eliminate everything it isn't, what is left should be what it is...
94-95 was the last of the TBI engines, and the last of the pre-OBDII engines, so there shouldn't be a whole lot more in the way of engine controls to check out.
It could be:
Mechanical--
Vacuum leak
Base timing
Binding/stuck throttle linkage
Throttle plates gummed up
Fuel pressure
TPS adjustment
Electrical/electronic--
Broken or corroded wire (power or ground)
Bad connection
Bad or out of range sensor
PCM misprogrammed, or incorrect, or going south

It could be a couple of other things, too, but this is a brief list of the usual suspects. I know you have checked many of them, how many have you not checked out yet?
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Old 08-20-2006, 02:56 PM   #70
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And he already checked that, it was perfect.
according to the "book". haynes manuals have been known to have errors in them!

i would look for an emmissions sticker under the hood and see if it is the same 4 degrees or not. my '88 ran at 0 degrees. worth looking into!

john
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