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Discussion Starter #1 (Edited)
High idle help- 1994 FSB 5.8L E40D ::!!UPDATE!!::

I have an intermittent high idle that is happening more and more frequently. When I 1st start it up in park it either normal (650-750 ish) or it idles high 1200-1500 ish.
If it idle good right off the bat, then almost always it will drive fine for the rest of the drive. If it idles high then it will idle high and drive weird the entire time of the drive.
When driving in the high idle condition, it idles in drive at around 1200 or so and all the shift points have been shifted up accordingly.
If I stop to go get some gas or whatever, when i start it up it may or may not idle high again.
So 1) I have concluded that there are no vacuum leaks- I have looked for them and the intermittent nature of the problem supports this. 2) I pulled the codes and get:
12: Cannot control RPM during ER Self-Test high RPM check.
21: ECT out of self test range 0.3 to 3.7 volts.
22: MAP/BP sensor out of self test range.

12 is a fail due to the engine running with a bad map or ect so that does not worry me. I am going to replace ECT and MAP after work and report back.

Does anyone have any other ideas that I maybe missing?
Should I reset the computer when I replace these parts?
Where is the ECT?

Many thanks to all for the help! FSB for life!


I disconnected the battery and replaced the MAP sensor and the ECT temp sensor as the trouble codes indicated. I hooked the battery back up and cranked it up and it seem to run fine. I drove it around and everything seems better.My idle is now rock solid and all is well in terms of idle now.
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9,894 Posts
If I remember right.

ECT = Engine coolant Temp if it thinks your engine is to cold it may be ramping up your idle.

Change the MAP and ECT then see what happens..

114 Posts
Im having a similar problem. When I start my engine it idles up to around 1500 then goes as high as 2000. I used to be able to bump the gas pedal to get it to idle back down but now it wont do that either. We have been through and checked and replaced any suspect vacuum line and the vacuum can has no holes in it. I havent hooked a code reader up to it yet but I guess that the next step. Last time I hooked a code reader up my computer somehow got fried.

Any other suggestions before I do that?

And welcome to this necro thread. 💀

Super Moderator
26,292 Posts
Yo Kenny,
See EEC IV scan tool operational info @
Innova Automotive Tools Owner Manual -
". f. Connecting or disconnecting test equipment when the ignition is “on” can cause a spark. This spark is potentially damaging to the test equipment and to the vehicle’s electronic components. Always turn the ignition “off” before connecting or disconnecting any test equipment.
g. To prevent damage to the on-board computer when taking vehicle electrical measurements, always use a digital
multimeter with at least 10 Megohms of impedance.

If all procedures are followed and the Code Reader will not
retrieve codes when performing the Key On Engine Off
(KOEO) Self Test, check the following:
1. Code Reader's batteries, change batteries as required.
2. Check the vehicles Test Connector pins for corrosion and
clean as necessary.
NOTE: The Code Reader receives a ground signal from one of
the pins of the vehicle's Test Connectors and uses it to signal
the computer to initiate the Self-Tests. A problem in the
vehicle's Test Connector ground pin or circuit will result in an
improper ground being supplied to the code reader which will
effect the code reader's ability to signal the computer to initiate
the Self Test. If after performing the procedures in step one and
two, the code reader still does not work proceed to EEC-IV
Systems/ MCU Systems bellow (as applicable).
EEC-IV Systems (most 1985-95 vehicles)
On some vehicles equipped with the EEC-IV Computer
Systems the vehicle's Test Connector ground circuit may have
a poor ground due to bad ground point connections, old and
corroded wiring, poor connector to wire contacts etc. that will
prevent the Code Reader from initiating the Self-Test. To
alleviate this problem and allow the Code Reader to initiate
the Self-Test, perform the following steps.
1. Disconnect the single pin
Vehicle's Test Connector from
the code reader (leave the six
pin Test Connector connected
to code reader).
2. Route a jumper wire from the
vehicle's harness single pin
Test Connector to the
vehicle's battery negative post
or to a clean spot in the
vehicle's metal frame. See
3. Proceed with KOEO Self Test as per KOEO instructions.
"A few users have complained of loose connections and a pin that gets easily pressed into the reader. This does, however, appear to be a minor issue. If you choose to purchase the extension cable, the pins should stay in place anyways. "

It's better to start a new thread for better visibility and responses.
If you want, I can try to move your posts and all responses to a new thread.
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