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Car idles very weird... No luck

542 Views 12 Replies 8 Participants Last post by  paul93VR4, 
davidster11
Been trying to figure this out for a while but haven't found the cause yet. The car is a 1995 Stealth RT/TT.

  • Before coming to a complete stop, when I let the car slow down in neutral, my idle jumps up and down between 1500-2000 RPM.
  • When I come to a complete stop, it will stay at 2000 RPM for a couple of seconds then go down to 1500 RPM and stays idling that way.

I believe it's staying at 1500 RPM once I'm stopped because of how the BISS is adjusted

Here's what I've done:
Checked throttle cable
Cleaned throttle body
I don't believe this would be the TPS (since its bouncing around)
I cleaned out the carbon buildup in my IAC (It wasn't too dirty anyways)
Spark plugs and wires replaced

MAF will probably be the next thing I check.

Kind of odd, I've dealt with bad idles in the past fine but never something like this... If anyone had something similar happen please share what you did to go about this.

Cheers!

- David
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Razith
Should test the resistance between the 4 coils for the IAC, make sure it's within the right range, which I believe is between 30-40 ohms. It can look spotless, and still be bad, just sorta how electronics are sometimes, it's a pain.

Unplug the MAF, see what it does. Should use default maps for things, so it'll point you in the right direction. I'd double check IAC though, when mine went out, it wanted to bounce the rpm a lot in certain gears, and stall out in reverse. 1500 is a pretty high base idle though(if warm), sounds like something else is off and the biss has just been bandaided to cover it up.

I save ECU checking for last, but it is on the list, and kinda a pain.
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bboyalan
It could easily be one or more things... dashpot and/or properly setting idle/BISS with ECU in base idle mode. There is always the possibility of a vacuum leak(s) too. Saying "I checked and cleaned" something tells us absolutely nothing.
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davidster11
Razith said:
Should test the resistance between the 4 coils for the IAC, make sure it's within the right range, which I believe is between 30-40 ohms. It can look spotless, and still be bad, just sorta how electronics are sometimes, it's a pain.

Unplug the MAF, see what it does. Should use default maps for things, so it'll point you in the right direction. I'd double check IAC though, when mine went out, it wanted to bounce the rpm a lot in certain gears, and stall out in reverse. 1500 is a pretty high base idle though(if warm), sounds like something else is off and the biss has just been bandaided to cover it up.

I save ECU checking for last, but it is on the list, and kinda a pain.
Click to expand...
What should happen when I unplug the MAF? Should I take it for a drive with it being unplugged to see what happens? Will double check IAC tomorrow as I don't have access to a multimeter right now
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davidster11
bboyalan said:
It could easily be one or more things... dashpot and/or properly setting idle/BISS with ECU in base idle mode. There is always the possibility of a vacuum leak(s) too. Saying "I checked and cleaned" something tells us absolutely nothing.
Click to expand...
How does one put the ECU in base idle mode? Never heard of anything like that on an OEM unit.
I don't have the proper tools to run a vacuum leak but was planning on buying them to test it out as I know it is a possibility to the problem I'm having.
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bboyalan
davidster11 said:
How does one put the ECU in base idle mode? Never heard of anything like that on an OEM unit.
I don't have the proper tools to run a vacuum leak but was planning on buying them to test it out as I know it is a possibility to the problem I'm having.
Click to expand...
Do a search on here or FSM for more information about it.

Check Connectors for the Mitsubishi 3000GT VR4 and Dodge Stealth TT by Jeff Lucius << pointing you in the right direction
(since "hybrid" year, you will need a scanner/logger instead of grounding terminal**)

One of the biggest mistakes by owners is arbitrarily messing with the BISS. Not saying that it was you though.
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Chang oil
Has the car always ran like this or all of a sudden it just started out the blue .....?

With high idle and snapping of the throttle closing with rpm bouncing round
Then it settling at 1500 rpm or slowly falling to that rpm ?

After a BISS screw tamper leads me to believe that there is a vacuum leak some where
Air getting sucked in on the other side of throttle body (intake side some where)
Very well could be throttle body shaft seals
(Along with many other issues that could be causing you to have high rpm idle)
02 sensors - vac leak - throttle body seals - MAF but would usually give you instant notification / bog / stalling bucking & jerking - catalytic converter coming apart would give you a no power on acceleration / clogged / coming apart from oil & fuel saturation

Need to pressure test the system ASAP
Running like this for a long period of time will in deed start messing things up for ya & other components if still equipped with emissions
That and high heat temperatures from running rich

Need to address the rpm issue before messing with BISS screw if it was set before there no reason to mess with it at all
This will send you on a wild goose chase
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davidster11
Chang oil said:
Has the car always ran like this or all of a sudden it just started out the blue .....?

With high idle and snapping of the throttle closing with rpm bouncing round
Then it settling at 1500 rpm or slowly falling to that rpm ?

After a BISS screw tamper leads me to believe that there is a vacuum leak some where
Air getting sucked in on the other side of throttle body (intake side some where)
Very well could be throttle body shaft seals
(Along with many other issues that could be causing you to have high rpm idle)
02 sensors - vac leak - throttle body seals - MAF but would usually give you instant notification / bog / stalling bucking & jerking - catalytic converter coming apart would give you a no power on acceleration / clogged / coming apart from oil & fuel saturation

Need to pressure test the system ASAP
Running like this for a long period of time will in deed start messing things up for ya & other components if still equipped with emissions
That and high heat temperatures from running rich

Need to address the rpm issue before messing with BISS screw if it was set before there no reason to mess with it at all
This will send you on a wild goose chase
Click to expand...
I definitely agree with not messing with the BISS screw.
The car usually settles at 1500 and doesn't really go down gradually. Funny enough... I drove the car about 20-30 minutes today and had no issue at all but I know the problem is still there. Kind of comes and goes...

I'm going to be doing the following on Monday:
1. Test IAC with a multimeter
2. Test MAF
3. Do a vacuum test

The car does jerk very slightly which makes me think it could be the MAF.

As you said it will be a bit of a goose chase, especially since the car is throwing no check engine light.
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A
Could be a previous owner messed with the throttle SAS too. Mine was idling at 1500-2000 RPM and after replacing the IAC and trying to set the BISS I ended up pulling the throttle body. Ended up looking through it with a light behind it and the blade was way the hell open for idle.

After setting the SAS to factory settings per the FSM, got her idling at ~900 rpm when warmed up.
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davidster11
CHECK ENGINE LIGHT CAME ON!
I used the paperclip method to read the codes.
Here are the codes I got: 43, 12, 13, 25

I've had code 43 pop up in the past but it left. This code was for EGR if I remember correctly and since then I've done an EGR delete and the code came back. I was also told this code could also be a faulty ECU.

I believe code 12 is volume airflow and code 25 is the barometric pressure sensor (which makes me think MAF)
I'm not sure about code 13...

If anyone has a list of codes that would be much appreciated or if you have any input too.
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J
davidster11 said:
Been trying to figure this out for a while but haven't found the cause yet. The car is a 1995 Stealth RT/TT.

  • Before coming to a complete stop, when I let the car slow down in neutral, my idle jumps up and down between 1500-2000 RPM.
  • When I come to a complete stop, it will stay at 2000 RPM for a couple of seconds then go down to 1500 RPM and stays idling that way.

I believe it's staying at 1500 RPM once I'm stopped because of how the BISS is adjusted

Here's what I've done:
Checked throttle cable
Cleaned throttle body
I don't believe this would be the TPS (since its bouncing around)
I cleaned out the carbon buildup in my IAC (It wasn't too dirty anyways)
Spark plugs and wires replaced

MAF will probably be the next thing I check.

Kind of odd, I've dealt with bad idles in the past fine but never something like this... If anyone had something similar happen please share what you did to go about this.

Cheers!

- David
Click to expand...
davidster11 said:
Been trying to figure this out for a while but haven't found the cause yet. The car is a 1995 Stealth RT/TT.

  • Before coming to a complete stop, when I let the car slow down in neutral, my idle jumps up and down between 1500-2000 RPM.
  • When I come to a complete stop, it will stay at 2000 RPM for a couple of seconds then go down to 1500 RPM and stays idling that way.

I believe it's staying at 1500 RPM once I'm stopped because of how the BISS is adjusted

Here's what I've done:
Checked throttle cable
Cleaned throttle body
I don't believe this would be the TPS (since its bouncing around)
I cleaned out the carbon buildup in my IAC (It wasn't too dirty anyways)
Spark plugs and wires replaced

MAF will probably be the next thing I check.

Kind of odd, I've dealt with bad idles in the past fine but never something like this... If anyone had something similar happen please share what you did to go about this.

Cheers!

- David
Click to expand...
how to test tps and iac
good luck
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Paul H.
davidster11 said:
I definitely agree with not messing with the BISS screw.
The car usually settles at 1500 and doesn't really go down gradually. Funny enough... I drove the car about 20-30 minutes today and had no issue at all but I know the problem is still there. Kind of comes and goes...

I'm going to be doing the following on Monday:
1. Test IAC with a multimeter
2. Test MAF
3. Do a vacuum test

The car does jerk very slightly which makes me think it could be the MAF.

As you said it will be a bit of a goose chase, especially since the car is throwing no check engine light.
Click to expand...
Do the vacuum leak test first.
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paul93VR4
davidster11 said:
CHECK ENGINE LIGHT CAME ON! If anyone has a list of codes that would be much appreciated
Click to expand...

12, volume air flow sensor,
13, intake air temp sensor
25 barometric pressure sensor
43, EGR system

Did you disconnect the MAF ? You have all three codes for that unit. Set condition is less than 3Hz for #12,
More than 4.6V or less than 0.2V for +4 seconds foe 13 & 25 That is a gross failure usually caused by pulling the plug, short or open.

P
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