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ASKED BY:

Rene Acosta

FSC MEMBER:

Yes

CATEGORY:

Engine

TAGS:

idle

Question

Hi Gil,
It’s me Rene again…
I’ve got a question for you (hopefully you can answer this).
1990 BMW 325i e30 (stock)
Only addition is a MAF sensor instead of a AFM.
My question is this…
Ever since I installed the MAF and removed the AFM, I’ve been having idle issues.
When I start the car it idles fine. I take it out for a drive 30 minutes or so.
I get home and let the car sit at idle for a few minutes and the idles starts to go up (as high as 1500rpm)
Turn the car off, start it again, and the idle is still high.
Not until the car cools down and I start it again does the idle go back to normal.
And then again if I let it just sit at idle it starts to go up.
Coolant Temp Sensor???
Throttle plate (butterfly) adjustment???
If it is the throttle plate what should the setting be? (How open should it be at rest/closed position?)
I have checked the TPS and it is sending a closed signal to the Computer when the plate is at rest. But that doesn’t mean that plate/butterfly is resting where it should be.
I have checked for vacuum leaks, as of today, I have not found any.

I’m really confused about this, and hopefully you can help.

Rene

Answer

Hi Mr. Acosta, I will need a little more info. What computer system are you using after the MAP conversion? Do you have the ability to datalog? If so I would like to see the logs please. A vacuum leak will not be the issue as the MAP reads total air inside of the intake and would take the leak into account. The E30 TPS is not a sensor but 2 switches, there is an idle and wide open throttle. Make sure that the idle switch is reading ok when the issue is occurring.

Do you have a manual for the car? If so, in the manual there will be a conversion table for the coolant temperature sensor, it will convert ohms to temperature, use it to check the sensor. Let me know what you find with them please.

Good luck.

Gil Neves

This Post Has 2 Comments

  1. Hi Gil,
    The car is a manual. And I just (Today) replaced the temp sensor and the issue still persists, so, the temp sensor was not causing it.
    Unfortunately, I do not have data logging abilities, as I have not been able to find a Diagnosis Reader for this old car (anywhere).
    I cannot read the TPS sensor while the issue is occurring because it is underneath the intake hose and I have to remove it to get to the plug.
    I know that before I installed the MAF Sensor and WAR Chip (From Miller) using their settings on the chip, it was not having this idle issue.
    I am at a loss, I don’t know what it could be.

    The idle creeps up slowly as the temp of car goes up, The car does not overheat.
    Only the idle creeps up slowly from the normal to about 1200.
    I have no idea what this could be.

    Any info will help.

    Rene Acosta

  2. Hello Mr. Acosta, we could diagnose the issue for you, but I would not be able to get to the car for 2 weeks. To diagnose the TPS you will have to tap into the wires and make an extension with another wire off of the signal wire so that you can read it with the car running, we really need to know what the TPS reading is as there is an adjustment for it and the possibility of failure. You can also look at the readings at the ECU, look at the coolant and TPS, if the coolant sensor is good you still need to verify the wiring, reading at the ECU will accomplish that. Where is the MAP getting the vacuum from ? Thank you.

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