Are we having fun yet??

[swervin ervin]

I'm having so much fun, I can't take much more.

Trying to get the van running right and it's about to woop me. It's TBI and I'm quickly learning what makes it tick. My biggest problem is I can't get it to idle at the proper rpm. It wants to run at around 1200 rpm all the time at idle. The idle speed is computer controlled with absolutely no mechanical way to adjust it. Let's see, here's what I've done.

Rebuilt the throttle body, new IAC valve, new TPS, new fuel filter, new O2 sensor, tried another ECM from the junkyard, new Prom for the ECM, etc.

Bought a Chiltons manual and started reading everything I could find on TBI fuel injection. Tried every test I could do with a digital volt meter. Nothing helped the idle. I was having a problem with a rough idle when it was cold, but did fix this, but not the speed.

After reading a bunch, according to what I could find the biggest problem with a idle too high is a intake air leak. Well, seeing as how I had a oil leak at the back of the intake, guess what, it's off. I'm going with new intake gaskets, new valve cover gaskets, and oil pan gasket.

I'll get this thing running right if it's the last thing I do.

Have I mentioned I hate TBI???

[pkbinplano]

Did you try squirting the intake down with carb cleaner to try to detect a leak ? Just a thought

[apstguy]

All I remeber hearing about them is that the butterfly valve seals or something go bad causing bad mileage. That is a weird problem. Is there a MAP sensor on it? Those go bad on newer motors frequently. Replacing all the sensors hooked up to it is all I can think of. You can try new fuel injectors (last resort - $$$)

[swervin ervin]

I hate to replace things like this, trying to fix something. But, I don't know of any other way to do it. If new intake gaskets don't fix it, it's back to the drawing board.

What really ticks me off is some previous owner thought if a check engine light comes on, you are supposed to take the bulb out of the dash so you can't see it. Duh. What kind of way is this to fix something??

It really gets me some of the stuff you see when you buy older trucks. Some folks just don't have a clue how to actually fix problems.

Sensors?

Here's the list of them all.

Engine Coolant Temperature Sensor
Oxygen Sensor
Manifold Absolute Pressure (MAP) Sensor
Vehicle Speed Sensor (VSS)
Throttle Position Sensor (TPS)

Along with other things, such as the Idle Air Control (IAC) valve. It's a complicated mess. After many years things get unplugged and removed. All this stuff must be working in order for it all to work right.

Just today, I found the Engine Coolant Temperature sensor was unplugged. This has a ton to do with everything in the whole system. This is the way the ECM knows how much fuel and timing the engine needs.

One thing is for sure, if I replace every dang switch and sensor on it, I'm bound to fix something.

I don't know about any butterfly valve seals. Didn't see any when I had it torn down. I guess if the throttle shafts get worn, it would probably kill mileage, since it would be getting more air and the ECM would automatically give it more fuel to compensate.

[gchemist]

HMMMM, maybe I can help the carb guru.
I got this information on setting the idle from this site. http://www.california.com/~eagle/howell.html

SETTING THE IDLE
This is a simple but critical adjustment covered briefly in the Howell instructions that at first I did wrong because I did not under stand the sequence of the adjustments.

The computer adjusts the idle depending upon RPM, throttle position, temperature and other conditions. The computer controls the idle using a small stepping motor that adjusts the idle air control. What this procedure does is to run the stepping motor to one end of its' travel and then you manually set the warm engine idle as a starting point to give the stepping motor enough range of control for all conditions.

The following setup procedure must be followed exactly: ( I did not understand this)

Warm up the engine
Turn off the key and stop the engine
Place the jumper between the A and B connections on the diagnostic connector.
Turn on the key but do not start the engine
(the stepping motor will now go all the way to one end of its' travel and you will be able to hear it clicking when it has reached the end)
Remove the four conductor cable from the idle air control stepping motor
(the stepping motor is now positioned and removing power will let it stay there during adjustment)
Start the engine
Adjust the idle speed screw located near the throttle control to set the low idle speed
( set the RPM so the warm engine will idle with out help , should be about 650 RPM)
Turn off the key and stop the engine
Replace the stepping motor connector and remove the jumper from the diagnostic connector

The engine should now start and run on idle under computer control. You should not have to help the computer make the engine idle and the engine should not stall when you remove your foot from the gas peddle. My engine idles at about 1000 RPM under open loop computer control.

[swervin ervin]

Thanks for info Gerardo, but been there, done that. I done this adjustment exactly like that.

This is not to set idle rpm, it's to set the minimum idle rpm. In other words, this is the absolute lowest it will run. The TPS on my TBI is non adjustable. I think some of the later years had adjustable ones. The IAC valve has no adjustment. Only thing you do when you replace it is drive it to around 40 mph. This resets the ECM and it will automatically adjust for the new IAC.

Bad thing about all this is, if/when I get it fixed, I won't have an idea what in the hell fixed it.

[apstguy]

Definitly get a new MAP sensor - those need to be replaced every once and a while to make sure it doesn't completly fail. That is what controls alot of the air/fuel mixture.

[swervin ervin]

Originally posted by apstguy
Definitly get a new MAP sensor - those need to be replaced every once and a while to make sure it doesn't completly fail. That is what controls alot of the air/fuel mixture.

On the list for tomorrow when I put it back together. New MAP sensor and coolant temp sensor. Might even get a new EGR valve. I'll fix this thing if it takes my last penny to do it.

I've been doing some more reading. It amazes me how the dang thing was even doing as good as it was. No wonder they pulled the check engine bulb. It was on all the time.

[73stepside]

did you check the iac motor? those little things get ver looked and sometimes go bad.

[old Rusty C10]

dont wanna discourage ya, but i got rid of a 2002 Venture cause iut wouldnt and the dealers couldnt get off the check engine light

[apstguy]

Have you checked the trouble codes Swerve? (not that is much use with the old engines) Might give you a hint - just use a paper clip or short wire.

[Lester]

Just curious.

If you are going to swap intake gaskets why not just swap manifolds, distributor, carb and add a pressure regulator?

Surely you have nearly enough spare parts laying around to do that.

Seems like you'd be way ahead.

Not to mention your sanity.

Insanity... doing the same thing over and over again with only one result possible, but expecting something else to happen.

Lester.

[swervin ervin]

Well, finished with the intake gaskets and valve cover gaskets. What a pain in the arse. I've never seen so much crap on top of a motor in my life. You think the carb motors have a lot of crap, that ain't nothing. Still has a high idle. From all the sources I have, this is a real good sign it's getting too much air.

So far I've replaced,

O2 sensor
TPS
IAC valve
Coolant temp sensor
Rebuilt the throttle body
Replace the ECM with one from a junkyard
New Prom
EGR valve
MAP sensor
Done every adjustment you can with a digital volt meter, and still it has a high idle. No more sensor to replace, except the EGR solenoid, but this don't have anything to do with a high idle.

I picking at straws now. I going tomorrow to the junkyard and get another throttle body. I checked mine and it has some play in the throttle shafts. Nothing execssive, but again, picking at straws here.

Reason I've not pulled any codes is because there wasn't a bulb in the dash for the check engine light. I'm also going to get some more bulb sockets to replace the check engine light the PO took out. I'll pull the codes tomorrow to see what's what.

Not giving up by any means.

[73stepside]

if the egr diaphram has ripped or torn, it will cause a vacuum leak.



edited cuase i can't read everything. solenoid won't cuase that. the one and only time i had a high idle with a fi vehicle was when i forgot to install the pcv after changine the valve cover gasket. doesn't help at all.

[swervin ervin]

Great news, at least for me. I fixed it. HOORAY for me.

Now don't ask me what exactly fixed it. Today I went to the junkyard and picked up a throttle body. I also picked up a gauge cluster, one with gauges instead of lights, out of a 88 van. So, I took the throttle body apart and cleaned it. I put all my stuff on this one because I felt like the old one had too much play in the throttle shaft. I installed the gauge cluster and got everything hooked up. The plug was different so I had to solder each wire to my wires in the dash. Same color wires, just arranged different in the plug. Also had to buy senders for it.

Anyway, fire it up and notice right away, the service engine soon light was blinking rapidly. It did seem to run a tad better though. So I shut it down and remove the ECM. I put my new prom in the old ECM. Fire it up and bam, it idled as smooth as silk, and not high. No check engine light or anything.

I have no idea what part fixed it. I think at first, if I had found the coolant temp sensor unplugged, it may have saved me a bunch of trouble and money. I don't know for sure if this was the fault or not. The new (used) throttle body may have helped too. I used two mounting gaskets just in case something was warped. I do know the ECM I got at the junkyard wouldn't work, even with a new prom.

I am very glad this is over. It's been driving me nuts. One thing about all this, every thing is new so maybe it will last awhile without messing up again. I learned a lot about TBI too. I never had a idea how complicated these things were.

Also got rid of some oil leaks in the process. Still got a oil pan gasket to put on, but this is a piece of cake compared to the rest of it.

Have I mentioned I hate computers on trucks?

Mike

[Russell]

lol, glad you got it going, I wouldn't even want to try to figure out how to fix a modern truck with an onboard computer...

I love the simplicity of my 1980

[apstguy]

Whoo ho! Finally! Now if you could fix my wipers! lol replace all the parts and still not right. TBI is nice until something goes wrong.