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Jay

Cold Brakes & High Idle?

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1 minute ago, 2seater said:

Yes there is a speed sensor in the transaxle. Now that you mention it, if you watch IAC counts, they will generally increase when the engine is running following an increase in throttle so it can smooth the transition back to idle when the throttle is released. In other words, it acts like a dashpot on a carburetor to keep the throttle from snapping shut.  

I just reviewed the IAC ES09 in the driveway.  Idling at 750-800 rprm.  IAC value at 78

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2 hours ago, Jay said:

However, once I start rolling the idle goes to 2,800-3,200 rpm.  If I sit in the driveway idle is rock steady at 725.  I put it in drive with foot on the brake and revved the engine to 1800 rpm.  Engine rpm smoothly drops to 725.  So this only happens when I am rolling.

This make sense. The only time the IAC can be controlled with override ES09 is when the transmission selector is in Park or Neutral. I imagine that is a safety feature. I'll bet as soon as you put the transmission in gear and the speed sensor starts producing a signal the ECM takes over the control of the IAC again.

 

You are making progress in troubleshooting this problem.  I think you have proved that the idle problem isn't caused by a vacuum leak.  The question is, is the ECM raising the RPM so high... and if so why is it doing that?

 

Here is what I would do next.  When the engine RPM has went to 2000 or 3000 for no apparent reason, go into Diagnostics->ECM Data->ED22 and see what the count is for the IAC. If the count is high you know the ECM is commanding the IAC to increase the RPM. If it is lower than normal or 0 you will know the ECM is trying to slow the idle down because something else is making it go too high.  Let us know what you find.

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So I drove down the street while in ED22 mode and watched in real time.  After about a 1.5 miles, the value did not drop lower than 51.  I did not see the RPM's obviously, but it is running so high that I do not have to use the throttle to get back to the house and requires a good amount of brake force to stop in the driveway.  I can even feel the car downshift due to the brake pressure as the motor is fighting against the increased braking.

Edited by Jay
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I finally remembered that this particular ECM came out of a 1990 Buick Riviera and not from a member.  I bought a BCM from another member. 

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My car is in storage so I can't experiment but those counts sound high. I don't believe there is any target value as it will depend on a bunch of factors but my gut says those are elevated counts. How far do you need to drop them to get the idle down??

 

Ooops, I see your idle value was 78 so there doesn't seem to be a direct comparable number.

Edited by 2seater

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52 minutes ago, Jay said:

I finally remembered that this particular ECM came out of a 1990 Buick Riviera and not from a member.  I bought a BCM from another member. 

I think the ecm should be fine as long as you installed your existing Calpak/PROM

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3 hours ago, Jay said:

So I drove down the street while in ED22 mode and watched in real time.  After about a 1.5 miles, the value did not drop lower than 51. 

What is the highest count you saw when the RPM was high?

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The highest value was somewhere around 98.  I should say that once it warmed up that the value did not drop lower than 51 as I did see lower values during the initial period before it warmed up. I think I will order a remanufactured ecm this time instead of a grabbing one out of a salvage yard.

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2 hours ago, Jay said:

The highest value was somewhere around 98.  I should say that once it warmed up that the value did not drop lower than 51 as I did see lower values during the initial period before it warmed up. I think I will order a remanufactured ecm this time instead of a grabbing one out of a salvage yard.

Interesting.  I did some testing on my Reatta this morning.

 

  • I started the engine and went into diagnostics->ECM data->ED22.
  • At fast idle, 850 RPM the IAC count was 55.
  • I drove the car down the road to allow everything to fully warm up and turned the engine off when I got back.
  • After a few minutes I restarted the engine. The gauges were showing a smooth idle at 675-725 RPM
  • I went into diagnostics and looked at ED22 and it was steady at 30-31.
  • Then I to override ES09 and ran the IAC up and down a few times and then stopped on 60.
  • With the IAC still on 60 I went up one level and then to ECM Data and looked at ED11(RPM). It was showing 1008 RPM.
  • To my surprise I discovered that while looking at ED11 I could still use the override arrows to change the IAC count.
  • I could watch the RPM and IAC count increase in real time and compare them as I used the override arrows.
  • I began lowering lowering the IAC count with the override. I stopped at 21 when the engine began to stumble at around 500 RPM.
  • As I began to raise the IAC count with the override arrows the engine smoothly gained RPM all the way up to a count of 99 and 2800 RPM where the RPM remained steady... just as I would expect it to do.
  • A count of 99 is the highest the override will allow you to go.

 

You should go through the same process as I did and see if you get the same results.  I think you will because you said your highest IAC count was about 98 and your RPM was about 3000.

 

What does all this mean?  I don't know for sure.  I know very little about the programming logic of the ECM. If your IAC vs RPM reading are similar to mine I think it would be fair to say the ECM is commanding the IAC to open, resulting in the high RPM, for some reason.  I can't think of any circumstance where the ECM should raise the RPM to 3000.  The turning on the A/C or turning the steering wheel will signal the ECM to raise the RPM to compensate for the extra load it puts on the engine but that should be only a  minor change in RPM.  If the car was mine, obtaining a used ECM from another Reatta that is know to be in good working order would be my next step. 

 

 

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I have extra ECMs available for sale. If interested e mail me at;

 lemke1044@aol.com

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Ronnie thanks for the test info!  I very much appreciate the effort. 

 

So I installed my original ECM (which has a remanufactured labe)l and went for a test drive of about 15 miles. I had purchased another ECM to verify that my IPC issue was not related to the ECM - and it wasn't.  Same exact response.  I literally rode home without touching the gas pedal and used brake only to get around the curves.  However, when I came to a stop in the driveway, it did drop to 725 rpm much quicker than it did yesterday. Ronnie I see the exact same numbers that you see and have the same responses to override controls.  Tomorrow I am going to run through the sensor test as suggested by 2Seater.  This seems to be movement related to the transmission.  I might even try jacking up the front wheels off the ground and see if I can duplicate the condition in the garage. (Note:  I will be backing the car in so that it is facing out the door and not towards my BMW K1200R Sport!!)  

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48 minutes ago, Jay said:

I literally rode home without touching the gas pedal and used brake only to get around the curves.

What were the IAC counts when this was happening?

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Testing on hold.  I had to replace the passenger window motor for the third time.  Hopefully I got the track and arm in a better position.  I greased the heck out of the tracks and guides initially, so I would think it has to be the alignment causing the burnout.  If this goes bad then I am going to pull the entire system out for inspection.  In any case, going out of town and will have to wait till I get back for running further tests.

 

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Did your idle problem get fixed?

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No.  Thanksgiving and work got me sidetracked.  It is still running very high.  I hope to look at it again this afternoon.  I will update as soon as I figure out what the heck is happening.  Thanks for checking!

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I removed the IAC that I had purchased.  I noticed that the bolt tabs seem to bend towards the mounting holes and the IAC solenoid was extremely extended.  I ordered a new IAC valve ($10 off Amazon) and installed.  High RPM fixed.  The only thing that I can think of is that somehow the first IAC that I purchased had bent tabs causing the IAC solenoid rod to come up shot in the intake hole allowing additional air. With the new one my it runs great and my mileage is back. Here is a screen shot from today's trip going from Knoxville back to Savannah. One thing to note is that my odometer/speedometer is off by 1.04 due to 17" wheels.  This means that my actual mpg is a little higher than what is shown, but not by much. Thanks to everyone on your help and input into solving this issue. 

IMG_20191230_132523810.jpg

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24 minutes ago, Jay said:

The only thing that I can think of is that somehow the first IAC that I purchased had bent tabs causing the IAC solenoid rod to come up shot in the intake hole allowing additional air. With the new one my it runs great and my mileage is back.

I'll bet you are right. Thanks for letting us know. I was scratching my head on that one wondering what was causing the crazy idle.  That is good gas mileage.

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To quote Svengoolie "Lookin' goody in the hoody"😎  Thanks for the resolution to file away in the memory, never to be seen again.

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27MPG, and average speed of 65.........thats excellent!  Now I have a good comparison for when I take a long trip.

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