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Old 10-10-2017, 04:21 AM   #1
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High idle - new information

Hi everyone

I have had a high idle problem for at least 3 years now. It's gotten worse. As I can't do an emergency brake like this during the vehicle inspection, I really have to fix that now.


The facts: 1988 Camaro, TBI, Vin E. My idle (park or neutral) won't drop after falling from over 2000 RPM to ~1250 RPM during the first 30 seconds. So that's when the IAC does it's job and seems to do it alright. After that while the car is warming up idle will go up further. Sometimes it will be around 1500, then up to 1700 or so. That causes the car to push while braking. I also have a worse mileage (has risen from about 14 to 16 l/100km, although it's not too bad). When in gear idle is around 1100-1400 RPM.


What I have checked / what I know so far:

- Put in a new IAC - no change.
- Pulled vacuum lines and plugged the ports - no change. Didn't look at the brake booster though.
- Air filter is only 2 years old.
- PCV valve was replaced about 3-4 years ago.
- My intake manifold is leaking.
- My injectors are spraying way too much fuel (my mechanic told me). The car is running even with one injector disconnected.
- My CTS seems to be fine.
- My ignition parts (rotor, spark plugs, wires) have never been serviced.
- I have never changed anything on my car, so all is stock. I've never changed or tried to change anything to the ignition timing.
- There doesn't seem to be dirt or anything in the TBI. The valves seem to close fine.
- I have a new MAP, O2 and TPS ready to hand. Not sure but think I have tried the new MAP already, but didn't make a change.


So yesterday I tried my new serial-USB-cable to read all the sensor values during the warming up in park position (only did the first 5 minutes). I can give these information:

- Idle started at 2000, then after 30 seconds was at 1400. Then fluctuating between 1225 and 1250. After 2 3/4 minutes slightly rising and fluctuating between 1275 and 1400.

- TPS voltage always stayed at 0.68. While accelerating (2625 RPM) at 1.15. It's not 0.54 as it should be, but okay as the ECM should recognize 0% under 1.25. While accelerating it has be higher... there seems to be something wrong.

- Cooling water temperature correctly rising from 60 to 130 degrees after 5 minutes.

- Battery voltage between 14.3 and 14.4

- Was in Open Loop until 105 degrees have been reached, then Closed Loop.

- Vaccum always was between 20 and 21.5 HG. At 2650 RPM it went down to 17 HG.

- IAT Temp started at 63 and went up to 72 degrees. Seems to be okay.

- IAC Position... was wondering about the high values at the beginning. Started at 158, then down to 128 (20 seconds), then falling slowly and constantly to 17 after 5 minutes.

- O2 sensor: Started at <500mV, then fluctuating a bit higher, around 550mV for 50 seconds, then suddenly dropped to 300 and fluctuating between 350 and 400, then again down to about 250, fluctuating around 300, then slowly dropping until the end of Open Loop after about 3 minutes to 200mV. In Closed Loop the values rise and fluctuate between 500 and 850. After accelerating and again in idle it dropped to <100 for a second or so, then again between 500 and 850.

- BLM and INT remained at 128 during Closed Loop. In Open Loop both were fluctuating slightly around 140. During acceleration BLM remained constant at 140, INT went down to 111. That was when the "Injector Sync Mode" said ASYNC.

- Rich/Lean showed lean most of the time, occasionally "rich" was showing for a second.

- MAP voltage... started at 1.0, then down to 0.8 after 15 seconds. Then fluctuating betweeen 0.75 and 0.9. During acceleration up to 1.45.

- MAP pressure... started at 30, then dropping until >26, then for a moment slightly fluctuating around 26, then again a bit lower till 24.74. During acceleration up to 35.


Questions:

- Someone told me that the ECM meters air based on manifold pressure. How does it do that? Only by changing the IAC? Or is there another option to get more air in?

- If I want to replace my TPS, will I have to adjust it? Because my service manual says nothing about adjusting it, only "making sure TPS pickup lever is located ABOVE tang on throttle actuator lever" and in another spot: "On all engines, the TPS is not adjustable. The ECM uses the reading at idle for the zero reading, so no adjustment is necessary." But I've read a lot about adjusting it...

Alright, so with all these information, what would you suggest to do next? Can you see something wrong with the sensor values? I really appreciate all your help.

Thanks,
Thomas

Last edited by Thomas Stahel; 10-10-2017 at 08:46 AM. Reason: Celsius to Fahrenheit
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Old 10-10-2017, 08:43 AM   #2
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Re: High idle - new information

I'm not a TBI guy, but I can help with a few things.

1. If you can, use Fahrenheit, not Celsius, I think most on this board talk in deg F.
2. You should fix your intake manifold leaks. Depending on how bad it is, it can definitely effect your ECM's idle ability.
3. The BLMs are only relevant in closed loop, not open loop.
4. You need to adjust the TPS whenever replaced. The IAC may need a reset procedure when replaced.
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Old 10-10-2017, 08:52 AM   #3
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Re: High idle - new information

Okay, number 1 is done.

2) I need another intake manifold, mine is cracked next to where the thermostat goes. If I have a major leak there, wouldn't also the vacuum be lower? Are there no values that would show that there is a leak?

3) As the BLMs have risen along with the idle in Closed Loop, I thought that would be something worth mentioning.

4) Okay, I think I did the procedure that I found here on the forum when I replaced the IAC for testing purposes. Well normally the idle should be lower when replacing an IAC without the procedure. In my case it made no kind of difference. Also I think my IAC should be okay because the counts that I got were down to 17 after 5 minutes. Still idle wasn't changing according to the decrease of IAC counts, except in the beginning during the first 30 seconds.

Thanks,
Thomas
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Old 10-10-2017, 09:03 AM   #4
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Re: High idle - new information

Sure thing!

Was the vacuum read at proper idle RPM?
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Old 10-10-2017, 09:09 AM   #5
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Re: High idle - new information

What do you mean by "sure thing!" exactly? Sorry, I'm not a native English speaker ;-)

The vacuum was read during the warming up in park position (5 minutes). It was always between 20 and 21.5 HG. So that was while the engine idled between 1225 and 1400 RPM. When I accelerated to 2400 RPM it went down to 17 HG. But as from what I read on the internet these values should be on the okay side, though they could surely be higher.

I have to add that I currently have no vacuum reservoir connected, but that was long after the high idle occured.
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Old 10-10-2017, 09:12 AM   #6
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Re: High idle - new information

You thanked me for helping you. I replied with "Sure thing!" meaning I am glad to help out.

Ok, yes then, vacuum looks good.

Have you checked for vacuum leaks?
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Old 10-10-2017, 09:19 AM   #7
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Re: High idle - new information

Oh, ok ;-)

So, wouldn't the vacuum be bad / worse, if the intake leak was bad?

I pulled the vacuum lines and plugged the ports at the TBI, well except for the brake booster. Now it could still be a leaking TBI somewhere, e.g. where it's mounted to the intake manifold. I wonder if the ECM can increase fuel when there's a leak somewhere and thus too much air. But is there a way for the ECM to determine too much air? I think this could only be sensed through bad O2 and MAP values which should be seen in my data given above.
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Old 10-10-2017, 09:25 AM   #8
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Re: High idle - new information

Brake boosters can be a big leak. You need to check that one too.

The engine will suck in uncontrolled air (leaks) and the MAP will see lower vacuum than expected at a given throttle position and try to compensate with less IAC bypass.
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Old 10-10-2017, 09:42 AM   #9
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Re: High idle - new information

Hm, okay I think I'll have to check the MAP values with engined turned off again. Because my values seem a bit low. They should be around 1-2 Volts while idling. And mine are around 0.8. They are not a lot too low but I don't know how much influence this has on the idle RPMs.

But the fact is, as it seems, that the vacuum is not too bad in idle, so RPM should be around 1000 and not 1250-1400. So I still don't get it... if I have an intake leak, vacuum and MAP values should be off to explain my high idle and amount of fuel...
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Old 10-10-2017, 09:46 AM   #10
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Re: High idle - new information

Personally....I would fix the intake leaks first, then go from there. Chances are that's where the idle issue lie.
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Old 10-10-2017, 09:50 AM   #11
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Re: High idle - new information

Thanks for your opinion. Always before I do something I need a logical explanation. So I still don't get how a possible bad intake leak goes together with my values that don't seem too bad. If I had such a big leak, why isn't my vacuum lower? And how can the ECM determine (apart from the O2 and MAP sensors) too much air so that it dumps that much fuel through the injectors?

As I understand, in Open Loop (that's when my RPMs are still about 300 too high), only CTS and MAP are used to control fuel through the injectors. So as the CTS values are perfect, it could only be the MAP values that tell the ECM to raise the amount of fuel. But they don't seem too bad. So if no value can tell the ECM to raise the amount of fuel and there was too much air from a leak, the RPMs would go too low instead of too high because of too much air and too few fuel. So something has to make the ECM or the injectors to dump more fuel in...

Last edited by Thomas Stahel; 10-10-2017 at 10:23 AM.
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Old 10-11-2017, 03:22 AM   #12
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Re: High idle - new information

Most cars here that have the idle stop screw cover removed should have this done. If not all of them because people shove a torx driver in there and start turning without knowing what there doing including me.

Even if this does not fix it at least its done.

The IACV is set properly within this procedure.
Its called...

"Setting Minimum Idle Speed".

1)Jump the A to B terminal under the dash in the ALDL Terminal as seen below.
2)Turn the key on but do not start it
3)You should hear a slight ticking coming from the IACV.
4)What 45 seconds then unplug the IACV with the ignition still on.
5)Disconnect the EST wire and remove the jumper.
6)Start the car.
It may be necessary to hold the throttle open slightly to prevent the engine from stalling.
Allow the engine to reach normal operating temperature.
7)Connect a tachometer. I used a digital timing gun with RPM feature.
8) Adjust the minimum idle speed using the throttle stop screw.
9) My Chilton’s says set it to 700rpm in park on an 89 TBI 5.0 auto.
10) When done shut the car off and reconnect the EST wire.
11) Plug the IACV back in.

Take it easy on the car for the first day or so.
Drive it normally on the street and highway to allow the ECM to re learn the new parameters.
The car will feel better and better as you do this.

If you use a paperclip as a jumper be sure to remove the very thin and hard to see plastic coating on it.
If you have to remove the air-cleaner assembly to get to the IACV conection be sure to cap off the open port on the front of the TBI if you remove that hose.

Last edited by Ron U.S.M.C.; 10-11-2017 at 03:37 AM.
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Old 10-11-2017, 09:34 AM   #13
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Re: High idle - new information

Does the IAC ever go to zero steps? If not then the high idle isn't being caused by a vacuum leak. Although there still can be a small leak as the IAC hasn't been extended far enough to bring the idle down.

The TPS auto-zero's in the '8063 ECM, so no need to adjust it. The .68V base setting of the TPS is OK.

At what coolant temperature does the engine typically run? This is important as the '8063 ECM won't hold an idle speed until the engine is almost up to temperature. Until that time there is a max cold idle speed. And a max warm idle speed.

These values are typically 1400 RPM (cold) and 1100 RPM (warm).

And notice that the engine coolant sensor (CTS) reading is important. As the ECM uses it to decide what is an acceptable idle speed.

Any chance you left a jumper or 10K resistor across the ALDL terminals A & B? Doing so will affect the idle speed.

RBob.
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Old 10-11-2017, 04:09 PM   #14
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Re: High idle - new information

@Ron: As I wrote: I and noone else have ever changed anything on the car, least of all at the Idle Speed Screw. So I think that is not the problem. And I don't think it would be a good idea to mess around with that as long as you don't know where the high idle comes from. I'd just be fiddling around with the wrong "buttons" maybe...

@RBob: Well, after 5 minutes I stopped the engine so as not to disturb the neighborhood ;-) After 5 minutes IAC was down to 17 steps. But the high idle is also during the warming up. About three years ago it was below 1000 RPM in park, which it should be because otherwise I can't pass the emission test. So 1250 to 1400 in park is quite high and it gets higher when the engine warms up although the IAC is dropping all the time. So I guess I should at least recheck and replace all the vacuum lines. I also have a new EGR, MAP and AGR, so I can try replacing these as well. But still, my vacuum value is at 20+ HG. If this value is okay, why should there be the smallest leak? And even if there was one why should it have such an impact on idle?

What do you mean by "at what temperature does the car usually run"? Normally when warmed up and driving on the highway (120 km/h) it's about 170 to 200 Fahrenheit. But the temperature rises erratically, sometimes up to 240 Fahrenheit, especially while driving in the city. I have a problem, maybe concerning the thermostat and I lose quite a lot of coolant and I drive a lot with really very little coolant, but I've driven the car for like 8 years with this condition. So I don't think this could have anything to do with the high idle.

I've used wires to read error codes earlier, so I don't think anything is left inside the terminal.

I don't understand why I can't determine what makes the injectors dump so much fuel in the engine as my mechanic says. Shouldn't the reason be seen in the sensor and ECM data?

Thanks,
Thomas
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Old 10-11-2017, 05:24 PM   #15
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Re: High idle - new information

Quote:
- My intake manifold is leaking.
Leaking what?

Quote:
- My injectors are spraying way too much fuel (my mechanic told me). The car is running even with one injector disconnected.
- My CTS seems to be fine.
I don't understand why I can't determine what makes the injectors dump so much fuel in the engine as my mechanic says. Shouldn't the reason be seen in the sensor and ECM data?

km/h) it's about 170 to 200 Fahrenheit. But the temperature rises erratically, sometimes up to 240 Fahrenheit, especially while driving in the city. I have a problem, maybe concerning the thermostat and I lose quite a lot of coolant and I drive a lot with really very little coolant,
OK, major problem here. With a low coolant level the CTS won't report the proper engine temperature. Really need to fix this first.

The resulting low coolant temperature being reported will cause the "too much fuel", and cause the high idle.

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Old 10-11-2017, 07:26 PM   #16
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Re: High idle - new information

[QUOTE=Ron U.S.M.C.;6175562]Most cars here that have the idle stop screw cover removed should have this done. If not all of them because people shove a torx driver in there and start turning without knowing what there doing including me.

Even if this does not fix it at least its done.

The IACV is set properly within this procedure.
Its called...

"Setting Minimum Idle Speed".

1)Jump the A to B terminal under the dash in the ALDL Terminal as seen below.
2)Turn the key on but do not start it
3)You should hear a slight ticking coming from the IACV.
4)What 45 seconds then unplug the IACV with the ignition still on.
5)Disconnect the EST wire and remove the jumper.
6)Start the car.
It may be necessary to hold the throttle open slightly to prevent the engine from stalling.
Allow the engine to reach normal operating temperature.
7)Connect a tachometer. I used a digital timing gun with RPM feature.
8) Adjust the minimum idle speed using the throttle stop screw.

Ron
Can you recommend a timing gun to buy. I do not have any type of device and it would be a good thing to have.
Thanks
Bob
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Old 10-12-2017, 01:19 AM   #17
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Re: High idle - new information

@RBob:

I had a laptop connected to the ECM and the CTS values were completely fine as I wrote above. At the moment the coolant level is good, it's only from time to time that the level drops. And as I also wrote: I've been driving the car for 8 years now with this exact problem (low coolant, overheating) and I've only had the high idle since about 3 years (slowly becoming higher).

My intake is leaking coolant at the back part of the manifold. You can see red color there and under the car you get very little drips of water around the oil filter, not sure if it's from the manifold. And at the front of the manifold it's leaking oil, not visibly leaking. If I clean everything up I need to drive a bit to build up oil there.

BTW: I'm not allowed to drive the car at the moment until I have had my car shown to the vehicle inspection.

Last edited by Thomas Stahel; 10-12-2017 at 01:25 AM.
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