How do I kill this automatic function?

[bennylava]

I have an 87 TBI 350 silverado. Which seems to pick and choose at random, when its going to engage that weird, higher RPM engine warming function. Its when the engine will idle higher, in some kind of seemingly unnecessary attempt to warm up... better? Faster?

I'm told that it has something to do with the cold, but it doesn't always do it when its really cold outside. It does it when there is... like an average temperature change. Here in TX I do not need the function. And its malfunctioning.

It won't do it in the summer, unless we get one of those rare cooler nights. Then it may do it. But as a general rule in the summer the truck won't do it. Its in the spring and the fall when its the worst. In the winter it doesn't really do it much either, although there are times when it will. Today I was sitting in the drive thru, and it was idling at 1500 rpm. I've seen it go to 1700 when its doing this. And its hard to get it to stop. It just decides all on its own when its going to stop, but this is usually after I've been driving for 10-20 minutes. Its really annoying and I'm sure people around me are wondering why my truck is making so much noise.

So how do you kill this ill conceived function? I don't need it, and I don't ever want to see it again. I just want the truck to always start up and idle the same.

[homemade87]

There is a temp sender that the computer sees to know when to enrich and bring the idle up . This sender may be out of calibration in those temp zones you are talking about .

Also you may want to look into the air idle control . It could be dirty or malfunctioning .

I don't think you can do away with this function . It has to work together as a whole .

If you get the problem fixed it will work as you want it to .

[geezer#99]

Could be your a/c circuit controlling the idle.
My 84 did the same thing. I simply unplugged the compressor on the a/c so it wouldn't cycle on/off and the idle never changed anymore.

[bennylava]

Originally Posted by homemade87

There is a temp sender that the computer sees to know when to enrich and bring the idle up . This sender may be out of calibration in those temp zones you are talking about .

Also you may want to look into the air idle control . It could be dirty or malfunctioning .

I don't think you can do away with this function . It has to work together as a whole .

If you get the problem fixed it will work as you want it to .

Do you happen to know where this sensor is located? Perhaps just replacing it would help. Its probably from 1987 so it could have gone lousy by now. The truck does have new coolant temp sensors. Well newer. IIRC I replaced them about 5 years ago.

[Desert1957]

Originally Posted by bennylava

Do you happen to know where this sensor is located? Perhaps just replacing it would help. Its probably from 1987 so it could have gone lousy by now. The truck does have new coolant temp sensors. Well newer. IIRC I replaced them about 5 years ago.

"New" doesn't always mean functioning correctly. Coolant sensor should be in the front of the intake near the thermostat housing.

Coolant temp sensor is separate from this sensor.

Make sure your cooling system is working normally, low coolant temps will effect the sensor making the computer think the engine is still cold.

[homemade87]

As Desert said , its right in front of the throttle body . This is the one the computer sees . The one in the rear of the head on the pass side is for the gauge .

Which one did you replace .


Cadillac has a good point . Check to see if any codes are set . There is a way to check with out a scanner with the flashes of SES light . May give us a direction to go .

[bennylava]

Originally Posted by homemade87

As Desert said, its right in front of the throttle body. This is the one the computer sees. The one in the rear of the head on the pass side is for the gauge.

Which one did you replace.


Cadillac has a good point. Check to see if any codes are set. There is a way to check with out a scanner with the flashes of SES light. May give us a direction to go.

Now I'm questioning if what I replaced was on another truck I used to have. An 81 lol. So I guess I'll scan the codes (I have scanner) and if nothing I'll replace...whichever one it is.

So to be clear, the one that governs the function I'm complaining about, is right in front of the throttle body? No wait, I went back an reread and desert said its a separate. Anyone know the exact location of this sensor, or otherwise how the computer gets the information to turn up the idle?

[cadillac_al]

It may even have a code stored to tell you what is out of spec.

[chris989]

Originally Posted by bennylava

I have an 87 TBI 350 silverado. Which seems to pick and choose at random, when its going to engage that weird, higher RPM engine warming function. Its when the engine will idle higher, in some kind of seemingly unnecessary attempt to warm up... better? Faster?

I'm told that it has something to do with the cold, but it doesn't always do it when its really cold outside. It does it when there is... like an average temperature change. Here in TX I do not need the function. And its malfunctioning.

It won't do it in the summer, unless we get one of those rare cooler nights. Then it may do it. But as a general rule in the summer the truck won't do it. Its in the spring and the fall when its the worst. In the winter it doesn't really do it much either, although there are times when it will. Today I was sitting in the drive thru, and it was idling at 1500 rpm. I've seen it go to 1700 when its doing this. And its hard to get it to stop. It just decides all on its own when its going to stop, but this is usually after I've been driving for 10-20 minutes. Its really annoying and I'm sure people around me are wondering why my truck is making so much noise.

So how do you kill this ill conceived function? I don't need it, and I don't ever want to see it again. I just want the truck to always start up and idle the same.

Download WINALDL free of charge. just buy or make a cable and then you can data log in real time and take the guessing out of it.

[andyh1956]

My 93 model was doing the same thing. Changing the sensor didn't help me. what did help was cutting the ends offa the grounds at the thermostat housing & crimping new ends on. Then get all the grounds on the manifold stud that has the neg bat cable on it. Fixed mine.

[4x4k30]

Originally Posted by andyh1956

My 93 model was doing the same thing. Changing the sensor didn't help me. what did help was cutting the ends offa the grounds at the thermostat housing & crimping new ends on. Then get all the grounds on the manifold stud that has the neg bat cable on it. Fixed mine.

most of the new temp sending units come with a new wiring pigtail to use and most up the time its just the wiring connection that causes problems

[chris989]

Benny,

Have you found the problem? I can say that without data logging you may never find it.

Here are a few things that will cause high idle. without reading the computer you will have to guess.

plastic shift indicator at the base of the steering column is broke or cracked and the truck thinks it is in gear when it is not

02 sensor to far from the manifold and not going into closed loop ,needs heated 02

temperature sender for the computer is off and reading cold.

possible vacuum leak.


TPS set wrong.

here are some screen shots of the program. you will find your problem in one minute. If you want to PM me i can walk you through it.

My TBI idled high and i wasted a lot of time and money guessing. My issue was the shift indicator and 02 sensor.



sticking IAC.

calling for AC by default.

[andyh1956]

Hey! I didn't know that TBI went to closed loop! Learn new stuff ever day!

[DieselSJ]

I have the same issue occasionally with my R30. Plus keep getting a EGR code and been chasing that with new parts. Just bought an ALDL cable. I'm done going at this blindly. Ordered it from here - http://www.aldlcable.com/

[bennylava]

My truck also has a problem with the EGR. Wonder if its related in some way to the issue...

[Edahall]

Once the engine is warmed up and idling normally, unhook the wires hooked up to the IAC valve. Now the idle will be set. Yes, you'll have to apply some gas pedal pressure during cold start ups but that's not hard to do and get used to. Plus, it prevents others from driving it.

[bennylava]

Originally Posted by Edahall

Once the engine is warmed up and idling normally, unhook the wires hooked up to the IAC valve. Now the idle will be set. Yes, you'll have to apply some gas pedal pressure during cold start ups but that's not hard to do and get used to. Plus, it prevents others from driving it.

Thanks Ed I'll give it a try. In your experience does this somehow... kill the problem I was talking about?

In my experience it idles fine when its cold. Again I'm in TX, and we don't really have cold winters. When it doesn't go into high idle mode on a cold day, it still idles fine. Maybe a bit lower than normal, but its a fuel injected truck and I usually just drive off anyway and its well on its way to warming up.

[Edahall]

Originally Posted by bennylava

Thanks Ed I'll give it a try. In your experience does this somehow... kill the problem I was talking about?

In my experience it idles fine when its cold. Again I'm in TX, and we don't really have cold winters. When it doesn't go into high idle mode on a cold day, it still idles fine. Maybe a bit lower than normal, but its a fuel injected truck and I usually just drive off anyway and its well on its way to warming up.

Just give it a try and report back. Make sure you disconnect the wires to the IAC while the engine is idling.

[chris989]

Originally Posted by DieselSJ

I have the same issue occasionally with my R30. Plus keep getting a EGR code and been chasing that with new parts. Just bought an ALDL cable. I'm done going at this blindly. Ordered it from here - http://www.aldlcable.com/

Benny,

Listen to the wisdom of Dieselsj, You will spend nothing but money and time throwing darts at it.

If you want to stop all IAC functions do as edahall suggested or set the IAC to zero this way.

1) With the IAC valve connected, ground the diagnostic (ALDL) terminal (same as you would do to flash trouble codes thru the check engine light).

2) Turn ON the ignition, but do NOT start the engine. Wait at least 30 seconds. The IAC will go to zero.

3) With the ignition still on, disconnect the IAC electrical connector. This will leave the IAC at zero and with no connection it will remain there.

4) Remove grounding of the diagnostic (ALDL) connector and start the engine.

5) Adjust the idle stop screw on the TBI.


If your IAC is working right it is nice to have. It adds counts for power steering, ac engaged, cold starts, when in gear.

I can't urge you enough to take advantage of the free (donation) software. There is most likely more going on than you will know and a little more MPG will pay for the cable.

good luck.

[DieselSJ]

Got my cable yesterday. It came with a CD that had more than a dozen different scanning/logging programs. I loaded up winaldl and went for a quick drive.

- I have CEL flags that weren't registering when I grounded the pins on the connector and read the flashes. The only code that showed up was for EGR. I also have codes for TPS low voltage and ESC.

- My knock counts are out of control. I'm seeing counts of several hundred on each cycle. Actually it cycles between just a few counts and several hundred.

- Confirmed that my temp sensor is reading correctly.

- IAC operation seemed fine

- I am slightly lean everywhere. This was expected due to the high-flow cat and 3" exhaust that I added. It seems to be within the parameters that the computer can handle though.

Hooked up the timing light and found that my initial timing (with plug disconnected) is sitting at about 10 degrees and is bouncing around. Didn't have time to adjust it. While I wouldn't think 6 degrees of extra timing would really hurt on a sub 8:1 compression engine, the combustion chamber might just suck enough to detonate anyway. Need to investigate further to determine if timing scatter is due to bad/failing ESC or timing chain.

[chris989]

Originally Posted by DieselSJ

Got my cable yesterday. It came with a CD that had more than a dozen different scanning/logging programs. I loaded up winaldl and went for a quick drive.

- I have CEL flags that weren't registering when I grounded the pins on the connector and read the flashes. The only code that showed up was for EGR. I also have codes for TPS low voltage and ESC.

- My knock counts are out of control. I'm seeing counts of several hundred on each cycle. Actually it cycles between just a few counts and several hundred.

- Confirmed that my temp sensor is reading correctly.

- IAC operation seemed fine

- I am slightly lean everywhere. This was expected due to the high-flow cat and 3" exhaust that I added. It seems to be within the parameters that the computer can handle though.

Hooked up the timing light and found that my initial timing (with plug disconnected) is sitting at about 10 degrees and is bouncing around. Didn't have time to adjust it. While I wouldn't think 6 degrees of extra timing would really hurt on a sub 8:1 compression engine, the combustion chamber might just suck enough to detonate anyway. Need to investigate further to determine if timing scatter is due to bad/failing ESC or timing chain.

you might be lean because of the advanced timing. I think it calls for TDC with the wire disconnected. I think the computer advances it up to 42 degrees at light cruise?? I will have to open a bin file to double check.

a few hundred knock counts is nothing to worry about. it is normalish. just starting the engine will cause some.

What motor do you have? My TBI is stock at 9.4-1

[DieselSJ]

Originally Posted by chris989

you might be lean because of the advanced timing. I think it calls for TDC with the wire disconnected. I think the computer advances it up to 42 degrees at light cruise?? I will have to open a bin file to double check.

a few hundred knock counts is nothing to worry about. it is normalish. just starting the engine will cause some.

What motor do you have? My TBI is stock at 9.4-1

Engine is a 87 TBI 7.4.

Doing more investigating and this engine does not have a knock sensor or the ESC circuit. So I think the knock counts are a BS number since this system has no way to sense for a knock. Looking at the logs it appears that the number just increments from 1 to 255 then resets.

It looks like part of my problem may be a bad ignition module which is causing the Code 42. Ran through the diagnostic chart last night and ended with the result of bad module, so I have a new Delco unit ordered.