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Old 08-07-2006, 06:32 PM   #15
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Fast Idle

OK, one more question before I tackle the TBI gasket. The Haynes Manual shows a top view of the TBI with the 2 injecters removed. I don't plan on removing my injectors. There are 3 bolts, roughly in a triangle, that hold the TBI in place. However, my TBI does not look EXACTLY like the one pictured in the Haynes Manual. My air filter, that mounts on top of the TBI, has 2 rods about 4 inches apart with wing nuts that hold it on. These rods go through the filter housing and are attached to the TBI in about the same location that 2 of the TBI mounting bolts are supposed to be. The bottom of the rod bases are formed like a bolt head and look like they could be bolts that screw out. I haven't tried them, but if these are not 2 of the TBI mounting bolts, then I am stumpt!! Comments please. Bill
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Old 08-07-2006, 07:15 PM   #16
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Bill, your TBI mounting bolts/nuts should be at each corner of the assembly, for a total of 4. The injectors should each have a pinch-clip plug that holds the wires on them. Unsnap the throttle cable, unscrew the two fuel lines (supply and return), unplug the throttle position sensor and IAC, and unscrew the four mounting bolts. The unit should come up off the intake manifold.
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Old 08-07-2006, 10:49 PM   #17
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Hello lebolewis ,

you are correct in your assumption on the IAC .It is an idle air control motor.
It is controlled by the computer (PCM) and does not move freely and do not
try it with the IAC out and plugged in to the wire harness ,turning on the key
as the pintle will be commanded to close by the PCM and the pintle will come right out ,you will need a new IAC.Vacuum leak is most likely the cause as
has been stated here and any of the above can do it .This is where a scan
tool comes in handy ,but it should be easy to find otherwise.

Scott
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Old 08-08-2006, 08:37 AM   #18
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Fast idle

OK guys, this is TBI gasket day! I will first do the testing with the WD40 and see what happens. If I get no indications of a vacuum leak (engine slows in RPM), then I will see if I can buy/borrow a Propane Torch and test with that (engine speeds up). If I do detect a leak, then I've got to see if my local Auto Parts places have the correct replacement gasket, before I remove the TBI. Don't want to be stranded with no truck and no gasket! To be continued......... Bill
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Old 08-08-2006, 09:52 AM   #19
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It won't be necessary to check it both ways. If the gasket it the problem you'll know with either test. ---Pieman
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Old 08-08-2006, 10:00 AM   #20
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Quote:
Originally Posted by scottanlily
Hello lebolewis ,

you are correct in your assumption on the IAC .It is an idle air control motor.
It is controlled by the computer (PCM) and does not move freely and do not
try it with the IAC out and plugged in to the wire harness ,turning on the key
as the pintle will be commanded to close by the PCM and the pintle will come right out ,you will need a new IAC.Vacuum leak is most likely the cause as
has been stated here and any of the above can do it .This is where a scan
tool comes in handy ,but it should be easy to find otherwise.

Scott
Scott, what is a "scan tool"? Bill
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Old 08-08-2006, 11:06 AM   #21
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Yikes! No Idle Adjustment - Fast

A scan tool is a (here it get indimidating) computer interface that lets you read the fault codes stored in the fault register in the engine computer. There is a register in the engine that stores failure codes when the computer detects something wrong. With this device (if you have spent enough money for one) can look at the output of selected sensors(02 sensor, throttle position, rpm, water temp to name a few). The most imporntant is the block learn number. This is a calculation of all the imputs from the sensors and determines the amount of gas the engine needs. Some later models also had an open time display. The block learn number will tell if the computer is calling for too much fuel(leaking gasket is causing an air leak creating a lean condition) or rich (leaking injector causing a too rich condition). I don't remember what the middle block number is, I'll have to look it up if you are interested.
Scott correct me if I'm wrong, but I believe that the OBDII didn't start until 1996. If that is the case, the OTC 2000 scanners (OBDI) can be purchased off Ebay. The last two I bought were less than 60.00$(I wanted a spare).
Beginner
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Old 08-08-2006, 02:14 PM   #22
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Sometimes you local auto parts place can scan your code in their lot. AutoZone around here does it for free. If course, they would have a hard time finding the ports on our 86 345 and 71 Beetle.
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Old 08-09-2006, 02:58 AM   #23
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Hello lebowlewis,

Well Beginner said it exactly ,that is what a scan tool is ,further ,its a hand held machine ,with a connector cable that plugs in to a connector under the
dash on most vehicals.
Beginner ,very good there with the" block learn "as that one thing confuses
even the up to date techs sometimes.You are correct 0BD II in 96 ,the best thing that could happen to computer diagnostics ,thats where we get in to
full data stream info ,misfire history ,02 sensor readings, pre cat and post cat
trans data ,evap controls ,on and on .My first scan tool was a monitor 2000
then the 4000 , they came out with the 4000E enhanced ,I have just upgraded from the genisys to the latest version with CAN protocal and
the most up to date information and capability .These units are a must
for anyone wanting to work on there own vehical .I have to have one for
my shop ,remember the codes and the datastream go hand in hand .I still have the old 4000 and the 2000 ,in case I have an 80s car to check out.You might want to get the 4000E Beginner, The 2000 is a very basic scan tool ,but still can be very useful .The genisys unit and the updated version
can do so much more ,but are very costley and primarily for obd ll and the latest cars and trucks. Also ,OBD l was 1995 year only ,thankfully.

Scott
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Old 08-09-2006, 03:10 AM   #24
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Hello swebster ,

The BAR, beaure of auto repair, has clamped down on auto zone about the free diagnostics ,as they were then selling parts ,only going by the trouble code,which for instance ,insufficiant EGR on a toyota ,they would sell an
EGR valve .Most always ,the EGR back pressure transducer is the problem.
The diaphram goes bad .So people were putting on these parts ,and the light came back on ,etc .They were told they were not an auto repair dealer
and could not be diagnosing vehicals .If they just did a code check for a
customer only ,that might be allowed .Many people like the idea ,at least
they know the code ,and what it could mean ,many did not like the same
problem still being there after buying the recommended parts.Same for
o2 codes ,a rich code stored ,can be a dirty air filter ,not the 02 itself.
A lean 02 code ,vacuum leak on a TBI airstream motorhome for example.
The IAC data would show on that motor home ,that the IAC is commanded
to be fully seated /extended ,showing that the computer is trying to get
the idle back down .So information is your greatest tool !

Scott
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Old 08-09-2006, 08:25 AM   #25
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Fast Idle

Update - not much happened with the vacuum leak yesterday. It was my Birthday and I had to do the obligatory lunch with sisters, etc., so all I accomplished was purchase the gasket. Had to order it, not in stock, from O'Reillys. The local GMC Dealer didn't have one in stock, either! After looking at the new gasket, I can see only one place, around the edges, where the width is about 1/4 inch and that would be the most likely place for a failure. That's the first place I will check with the WD40. Everywhere else around the gasket, it is about 1/2 inch thick, or more, to the outside. ......To be continued......Bill
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Old 08-09-2006, 03:51 PM   #26
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Quote:
Originally Posted by lebolewis
Update - not much happened with the vacuum leak yesterday. It was my Birthday and I had to do the obligatory lunch with sisters, etc., so all I accomplished was purchase the gasket. Had to order it, not in stock, from O'Reillys. The local GMC Dealer didn't have one in stock, either! After looking at the new gasket, I can see only one place, around the edges, where the width is about 1/4 inch and that would be the most likely place for a failure. That's the first place I will check with the WD40. Everywhere else around the gasket, it is about 1/2 inch thick, or more, to the outside. ......To be continued......Bill
Well, @#$%^*! , just as I feared.....I did the WD40 thing all around the TBI gasket and found no indication of a vacuum leak! NOTHING! That gasket was floating in WD40....I then sprayed all the vacuum hose connections to the TBI and the rubber hoses on them to the end and NOTHING! This is typical for me, NOTHING is ever EASY! I didn't try to check the intake manifold gasket because it is so extensive and covered with so much stuff.

Now, here is what I am thinking. Could my idle speed be NORMAL for this big engine?!! I did some more checking and found that after the engine is hot, the idle speed in neutral is 1000 RPMs, measured by the Tach in the inst panel. It drops to about 900 RPMs when in gear. Then it drops to about 800 RPMs with the AC on, Hi fan, front and back, and head lights on. Can anybody tell me what the NORMAL idle speed is for this engine under these conditions?

Also, we have an AutoZone here. If they offer a "free" diagnostics, would this confirm that my engine idle RPMs are too high and that I have a vacuum leak? Bill
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Old 08-09-2006, 06:02 PM   #27
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Autozone will hook a scanner up to your vehicle, and read the codes. I think idle should be around 850 in neutral, I will check Alldata tomorrow morning, and post here if it is different, if no one else has made a definitive post in the meantime. BTW, did you ever unplug the vacuum line to the brake booster? Does your coach have vacuum boost, or is it Hydroboost?
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Old 08-09-2006, 08:01 PM   #28
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Quote:
Originally Posted by overlander63
Autozone will hook a scanner up to your vehicle, and read the codes. I think idle should be around 850 in neutral, I will check Alldata tomorrow morning, and post here if it is different, if no one else has made a definitive post in the meantime. BTW, did you ever unplug the vacuum line to the brake booster? Does your coach have vacuum boost, or is it Hydroboost?
Terry, my brakes are Hydroboost, gets it's boost from the Power Steering Pump.

I called AutoZone to inquire about a "free" computer code scan. They will do it but their equipment will only scan 1996 models and newer. No help here, my GMC is a 1994.

Bill
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